[indvars] Missing variables at Og: #69920

CarlosAlbertoEnciso · 2023-10-23T12:23:45Z

https://bugs.llvm.org/show_bug.cgi?id=51735
#51077

In the given test case:

4 ...
5 void bar() {
6   int End = 777;
7   int Index = 27;
8   char Var = 1;
9   for (; Index < End; ++Index)
10     ;
11   nop(Index);
12 }
13 ...

Missing local variable Index after loop Induction Variable Elimination.
When adding a breakpoint at line 11, LLDB does not have information
on the variable. But it has info on Var and End.

llvmbot · 2023-10-23T12:24:25Z

@llvm/pr-subscribers-llvm-support
@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-debuginfo

Author: Carlos Alberto Enciso (CarlosAlbertoEnciso)

Changes

https://bugs.llvm.org/show_bug.cgi?id=51735
#51077

In the given test case:

4 ...
5 void bar() {
6   int End = 777;
7   int Index = 27;
8   char Var = 1;
9   for (; Index &lt; End; ++Index)
10     ;
11   nop(Index);
12 }
13 ...

Missing local variable Index after loop Induction Variable Elimination. When adding a breakpoint at line 11, LLDB does not have information on the variable. But it has info on Var and End.

Full diff: https://github.com/llvm/llvm-project/pull/69920.diff

3 Files Affected:

(modified) llvm/lib/Transforms/Scalar/IndVarSimplify.cpp (+25)
(added) llvm/test/Transforms/LoopSimplify/pr51735-1.ll (+115)
(added) llvm/test/Transforms/LoopSimplify/pr51735.ll (+106)

diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
index 41c4d6236173472..0e20b5e62040374 100644
--- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -46,6 +46,7 @@
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
@@ -1931,6 +1932,30 @@ bool IndVarSimplify::run(Loop *L) {
     }
   }
 
+  // The loop exit values have been updated; insert the debug location
+  // for the induction variable with its final value.
+  if (PHINode *IndVar = L->getInductionVariable(*SE)) {
+    const SCEV *IndVarSCEV = SE->getSCEVAtScope(IndVar, L->getParentLoop());
+    if (IndVarSCEV->getSCEVType() == SCEVTypes::scConstant) {
+      Value *FinalIVValue = cast<SCEVConstant>(IndVarSCEV)->getValue();
+      SmallVector<DbgVariableIntrinsic *> DbgUsers;
+      SmallVector<DbgVariableIntrinsic *> DbgUsersCloned;
+      findDbgUsers(DbgUsers, IndVar);
+      for (auto &DebugUser : DbgUsers) {
+        auto *Cloned = cast<DbgVariableIntrinsic>(DebugUser->clone());
+        Cloned->replaceVariableLocationOp(static_cast<unsigned>(0),
+                                          FinalIVValue);
+        DbgUsersCloned.push_back(Cloned);
+      }
+
+      SmallVector<BasicBlock *> ExitBlocks;
+      L->getExitBlocks(ExitBlocks);
+      for (BasicBlock *Exit : ExitBlocks)
+        for (auto &DebugUser : DbgUsersCloned)
+          DebugUser->insertBefore(Exit->getFirstNonPHI());
+    }
+  }
+
   // Eliminate redundant IV cycles.
   NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts, TTI);
 
diff --git a/llvm/test/Transforms/LoopSimplify/pr51735-1.ll b/llvm/test/Transforms/LoopSimplify/pr51735-1.ll
new file mode 100644
index 000000000000000..de9a74522095659
--- /dev/null
+++ b/llvm/test/Transforms/LoopSimplify/pr51735-1.ll
@@ -0,0 +1,115 @@
+; RUN: opt -passes=indvars -S -o - < %s | FileCheck %s
+
+; Missing local variable 'Index' after loop 'Induction Variable Elimination'.
+; When adding a breakpoint at line 11, LLDB does not have information on
+; the variable. But it has info on 'Var' and 'End'.
+
+;  1	__attribute__((optnone)) int nop(int Param) {
+;  2	  return 0;
+;  3	}
+;  4
+;  5	void bar() {
+;  6    int End = 777;
+;  7	  int Index = 27;
+;  8	  char Var = 1;
+;  9	  for (; Index < End; ++Index)
+; 10	    ;
+; 11	  nop(Index);
+; 12	}
+; 13
+; 14	int main () {
+; 15	  bar();
+; 16	}
+
+; CHECK: for.cond: {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 poison, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 poison, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK:   br i1 false, label %for.cond, label %for.end, {{.*}}
+; CHECK: for.end: {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 777, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK:   %call = tail call noundef i32 @_Z3nopi(i32 noundef 777), {{.*}}
+; CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Index"{{.*}})
+
+define dso_local noundef i32 @_Z3nopi(i32 noundef %Param) local_unnamed_addr #0 !dbg !10 {
+entry:
+  %Param.addr = alloca i32, align 4
+  store i32 %Param, ptr %Param.addr, align 4
+  call void @llvm.dbg.declare(metadata ptr %Param.addr, metadata !15, metadata !DIExpression()), !dbg !16
+  ret i32 0, !dbg !17
+}
+
+define dso_local void @_Z3barv() local_unnamed_addr #2 !dbg !18 {
+entry:
+  call void @llvm.dbg.value(metadata i32 777, metadata !21, metadata !DIExpression()), !dbg !22
+  call void @llvm.dbg.value(metadata i32 27, metadata !23, metadata !DIExpression()), !dbg !22
+  call void @llvm.dbg.value(metadata i32 1, metadata !24, metadata !DIExpression()), !dbg !22
+  br label %for.cond, !dbg !25
+
+for.cond:                                         ; preds = %for.cond, %entry
+  %Index.0 = phi i32 [ 27, %entry ], [ %inc, %for.cond ], !dbg !22
+  call void @llvm.dbg.value(metadata i32 %Index.0, metadata !23, metadata !DIExpression()), !dbg !22
+  %cmp = icmp ult i32 %Index.0, 777, !dbg !26
+  %inc = add nuw nsw i32 %Index.0, 1, !dbg !29
+  call void @llvm.dbg.value(metadata i32 %inc, metadata !23, metadata !DIExpression()), !dbg !22
+  br i1 %cmp, label %for.cond, label %for.end, !dbg !30, !llvm.loop !31
+
+for.end:                                          ; preds = %for.cond
+  %Index.0.lcssa = phi i32 [ %Index.0, %for.cond ], !dbg !22
+  %call = tail call noundef i32 @_Z3nopi(i32 noundef %Index.0.lcssa), !dbg !34
+  ret void, !dbg !35
+}
+
+define dso_local noundef i32 @main() local_unnamed_addr #3 !dbg !36 {
+entry:
+  call void @_Z3barv(), !dbg !39
+  ret i32 0, !dbg !40
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 18.0.0 (https://github.com/llvm/llvm-project.git 18c2eb2bf02bd7666523aa566e45d62053b7db80)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 2}
+!9 = !{!"clang version 18.0.0"}
+!10 = distinct !DISubprogram(name: "nop", linkageName: "_Z3nopi", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !14)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13, !13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !{}
+!15 = !DILocalVariable(name: "Param", arg: 1, scope: !10, file: !1, line: 1, type: !13)
+!16 = !DILocation(line: 1, column: 38, scope: !10)
+!17 = !DILocation(line: 2, column: 3, scope: !10)
+!18 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barv", scope: !1, file: !1, line: 5, type: !19, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !14)
+!19 = !DISubroutineType(types: !20)
+!20 = !{null}
+!21 = !DILocalVariable(name: "End", scope: !18, file: !1, line: 6, type: !13)
+!22 = !DILocation(line: 0, scope: !18)
+!23 = !DILocalVariable(name: "Index", scope: !18, file: !1, line: 7, type: !13)
+!24 = !DILocalVariable(name: "Var", scope: !18, file: !1, line: 8, type: !13)
+!25 = !DILocation(line: 9, column: 3, scope: !18)
+!26 = !DILocation(line: 9, column: 16, scope: !27)
+!27 = distinct !DILexicalBlock(scope: !28, file: !1, line: 9, column: 3)
+!28 = distinct !DILexicalBlock(scope: !18, file: !1, line: 9, column: 3)
+!29 = !DILocation(line: 9, column: 23, scope: !27)
+!30 = !DILocation(line: 9, column: 3, scope: !28)
+!31 = distinct !{!31, !30, !32, !33}
+!32 = !DILocation(line: 10, column: 5, scope: !28)
+!33 = !{!"llvm.loop.mustprogress"}
+!34 = !DILocation(line: 11, column: 3, scope: !18)
+!35 = !DILocation(line: 12, column: 1, scope: !18)
+!36 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 14, type: !37, scopeLine: 14, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!37 = !DISubroutineType(types: !38)
+!38 = !{!13}
+!39 = !DILocation(line: 15, column: 3, scope: !36)
+!40 = !DILocation(line: 16, column: 1, scope: !36)
diff --git a/llvm/test/Transforms/LoopSimplify/pr51735.ll b/llvm/test/Transforms/LoopSimplify/pr51735.ll
new file mode 100644
index 000000000000000..b9bdc8ca1b6fb09
--- /dev/null
+++ b/llvm/test/Transforms/LoopSimplify/pr51735.ll
@@ -0,0 +1,106 @@
+; RUN: opt -passes=indvars -S -o - < %s | FileCheck %s
+
+; Missing local variable 'Index' after loop 'Induction Variable Elimination'.
+; When adding a breakpoint at line 11, LLDB does not have information on
+; the variable. But it has info on 'Var' and 'End'.
+
+;  1	__attribute__((optnone)) int nop() {
+;  2	  return 0;
+;  3	}
+;  4
+;  5	void bar() {
+;  6    int End = 777;
+;  7	  int Index = 27;
+;  8	  char Var = 1;
+;  9	  for (; Index < End; ++Index)
+; 10	    ;
+; 11	  nop();
+; 12	}
+; 13
+; 14	int main () {
+; 15	  bar();
+; 16	}
+
+; CHECK: for.cond: {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 poison, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 poison, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK:   br i1 false, label %for.cond, label %for.end, {{.*}}
+; CHECK: for.end: {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 777, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK:   %call = tail call noundef i32 @_Z3nopv(), {{.*}}
+; CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Index"{{.*}})
+
+define dso_local noundef i32 @_Z3nopv() local_unnamed_addr #0 !dbg !10 {
+entry:
+  ret i32 0, !dbg !14
+}
+
+define dso_local void @_Z3barv() local_unnamed_addr #1 !dbg !15 {
+entry:
+  call void @llvm.dbg.value(metadata i32 777, metadata !19, metadata !DIExpression()), !dbg !20
+  call void @llvm.dbg.value(metadata i32 27, metadata !21, metadata !DIExpression()), !dbg !20
+  call void @llvm.dbg.value(metadata i32 1, metadata !22, metadata !DIExpression()), !dbg !20
+  br label %for.cond, !dbg !23
+
+for.cond:                                         ; preds = %for.cond, %entry
+  %Index.0 = phi i32 [ 27, %entry ], [ %inc, %for.cond ], !dbg !20
+  call void @llvm.dbg.value(metadata i32 %Index.0, metadata !21, metadata !DIExpression()), !dbg !20
+  %cmp = icmp ult i32 %Index.0, 777, !dbg !24
+  %inc = add nuw nsw i32 %Index.0, 1, !dbg !27
+  call void @llvm.dbg.value(metadata i32 %inc, metadata !21, metadata !DIExpression()), !dbg !20
+  br i1 %cmp, label %for.cond, label %for.end, !dbg !28, !llvm.loop !29
+
+for.end:                                          ; preds = %for.cond
+  %call = tail call noundef i32 @_Z3nopv(), !dbg !32
+  ret void, !dbg !33
+}
+
+define dso_local noundef i32 @main() local_unnamed_addr #2 !dbg !34 {
+entry:
+  call void @_Z3barv(), !dbg !35
+  ret i32 0, !dbg !36
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7, !8}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 18.0.0 (https://github.com/llvm/llvm-project.git 18c2eb2bf02bd7666523aa566e45d62053b7db80)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"PIE Level", i32 2}
+!7 = !{i32 7, !"uwtable", i32 2}
+!8 = !{i32 7, !"frame-pointer", i32 2}
+!9 = !{!"clang version 18.0.0"}
+!10 = distinct !DISubprogram(name: "nop", linkageName: "_Z3nopv", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !DILocation(line: 2, column: 3, scope: !10)
+!15 = distinct !DISubprogram(name: "bar", linkageName: "_Z3barv", scope: !1, file: !1, line: 5, type: !16, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !18)
+!16 = !DISubroutineType(types: !17)
+!17 = !{null}
+!18 = !{}
+!19 = !DILocalVariable(name: "End", scope: !15, file: !1, line: 6, type: !13)
+!20 = !DILocation(line: 0, scope: !15)
+!21 = !DILocalVariable(name: "Index", scope: !15, file: !1, line: 7, type: !13)
+!22 = !DILocalVariable(name: "Var", scope: !15, file: !1, line: 8, type: !13)
+!23 = !DILocation(line: 9, column: 3, scope: !15)
+!24 = !DILocation(line: 9, column: 16, scope: !25)
+!25 = distinct !DILexicalBlock(scope: !26, file: !1, line: 9, column: 3)
+!26 = distinct !DILexicalBlock(scope: !15, file: !1, line: 9, column: 3)
+!27 = !DILocation(line: 9, column: 23, scope: !25)
+!28 = !DILocation(line: 9, column: 3, scope: !26)
+!29 = distinct !{!29, !28, !30, !31}
+!30 = !DILocation(line: 10, column: 5, scope: !26)
+!31 = !{!"llvm.loop.mustprogress"}
+!32 = !DILocation(line: 11, column: 3, scope: !15)
+!33 = !DILocation(line: 12, column: 1, scope: !15)
+!34 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 14, type: !11, scopeLine: 14, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0)
+!35 = !DILocation(line: 15, column: 3, scope: !34)
+!36 = !DILocation(line: 16, column: 1, scope: !34)

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

llvm/test/Transforms/LoopSimplify/pr51735-1.ll

CarlosAlbertoEnciso · 2023-10-26T06:51:07Z

@nikic Thanks for your feedback.
I uploaded a new patch addressing:

Moved the new logic to rewriteLoopExitValues.
Removed from the test cases, the unrelated functions: nop and main.
Use isa<SCEVConstant>.

nikic · 2023-10-26T07:01:40Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+
+  // The loop exit values have been updated; insert the debug location
+  // for the induction variable with its final value.
+  if (PHINode *IndVar = L->getInductionVariable(*SE)) {


This is still the wrong place to do this. You are updating just a single "induction variable" here, while the code can rewrite multiple, and can also use different exit values for different blocks. This adjustment should be above in the // Transformation. loop, which has all the induction phis and their replacement values.

felipepiovezan · 2023-10-26T17:49:44Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+  if (PHINode *IndVar = L->getInductionVariable(*SE)) {
+    const SCEV *IndVarSCEV = SE->getSCEVAtScope(IndVar, L->getParentLoop());
+    if (isa<SCEVConstant>(IndVarSCEV)) {
+      Value *FinalIVValue = cast<SCEVConstant>(IndVarSCEV)->getValue();


Note that you should not use an isa<> test followed by a cast<>, for that use the dyn_cast<> operator.

https://llvm.org/docs/ProgrammersManual.html#the-isa-cast-and-dyn-cast-templates

I think this would be easier to follow with an early exit on the result of the dyn cast: https://llvm.org/docs/CodingStandards.html#use-early-exits-and-continue-to-simplify-code

felipepiovezan · 2023-10-26T17:50:13Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+      findDbgUsers(DbgUsers, IndVar);
+      for (auto &DebugUser : DbgUsers) {
+        auto *Cloned = cast<DbgVariableIntrinsic>(DebugUser->clone());
+        Cloned->replaceVariableLocationOp(static_cast<unsigned>(0),


felipepiovezan · 2023-10-26T17:50:54Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+      SmallVector<DbgVariableIntrinsic *> DbgUsers;
+      SmallVector<DbgVariableIntrinsic *> DbgUsersCloned;
+      findDbgUsers(DbgUsers, IndVar);
+      for (auto &DebugUser : DbgUsers) {


we don't need a reference to a pointer here (we are not modifying the pointer), we can use auto * to express this intent

felipepiovezan · 2023-10-26T17:53:51Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+      SmallVector<BasicBlock *> ExitBlocks;
+      L->getExitBlocks(ExitBlocks);
+      for (BasicBlock *Exit : ExitBlocks)
+        for (auto &DebugUser : DbgUsersCloned)


similarly here auto *

felipepiovezan · 2023-10-26T17:54:30Z

llvm/test/Transforms/LoopSimplify/pr51735-1.ll

+; 15	  bar();
+; 16	}
+
+; CHECK: for.cond: {{.*}}


do we need this {{.*}}? (and in the other BB labels)

felipepiovezan · 2023-10-26T17:57:09Z

llvm/test/Transforms/LoopSimplify/pr51735-1.ll

+; CHECK:   call void @llvm.dbg.value(metadata i32 %Index.{{[0-9]+}}, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 %inc, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK: for.end: {{.*}}
+; CHECK:   call void @llvm.dbg.value(metadata i32 777, metadata ![[DBG:[0-9]+]], {{.*}}


if I understand this test correctly, all of these dbg.values are for the variable Index, right? I think it's important that we label the first occurrence of it and check that all three of these intrinsics are referring to it (right now we allow any metadata there)

Note that we are redefining what ![[DBG]] is in each of these CHECKs

felipepiovezan · 2023-10-26T17:58:04Z

llvm/test/Transforms/LoopSimplify/pr51735-1.ll

+
+define dso_local void @_Z3barv() local_unnamed_addr #2 !dbg !18 {
+entry:
+  call void @llvm.dbg.value(metadata i32 777, metadata !21, metadata !DIExpression()), !dbg !22


Is this and the third intrinsic relevant for the test? (i.e. the intrinsics that don't target !23 = Index

felipepiovezan · 2023-10-26T18:00:36Z

llvm/test/Transforms/LoopSimplify/pr51735.ll

+; CHECK:   call void @llvm.dbg.value(metadata i32 777, metadata ![[DBG:[0-9]+]], {{.*}}
+; CHECK-DAG: ![[DBG]] = !DILocalVariable(name: "Index"{{.*}})
+
+define dso_local void @_Z3barv() local_unnamed_addr #1 !dbg !15 {


Could you elaborate on how these tests differ from each other? I couldn't tell by comparing the two

(IIRC, the difference is that there are multiple exit blocks, to stimulate more of the paths through the code-changes).

CarlosAlbertoEnciso · 2024-01-03T12:19:06Z

I am sorry for my delay in addressing the comments from the reviewers, but I was on PTO.
The reworked patch addresses the issues and includes 2 test cases:

Multiple exit blocks
Single exit block.

nikic · 2024-01-03T13:45:47Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+    // get updated, which is fine as that is the existing behaviour.
+    if (DebugUser->hasArgList())
+      continue;
+    for (BasicBlock *Exit : ExitBlocks) {


The ExitValue is specific to one exit block. Why are you updating all of them here?

Reworked the code to take into account that point. Reworked in new patch.

nikic · 2024-01-03T13:46:04Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

@@ -1482,6 +1513,21 @@ int llvm::rewriteLoopExitValues(Loop *L, LoopInfo *LI, TargetLibraryInfo *TLI,
          (isa<PHINode>(Inst) || isa<LandingPadInst>(Inst)) ?
          &*Inst->getParent()->getFirstInsertionPt() : Inst;
        RewritePhiSet.emplace_back(PN, i, ExitValue, InsertPt, HighCost);
+
+        // Add debug values if the PN is a induction variable.


Why is this code needed in addition to the addDebugValuesToLoopVariable() below?

That code creates a debug value in the exit block if any of the incoming values for the PHI Node being replaced is the induction variable. Reworked in new patch.

CarlosAlbertoEnciso · 2024-01-09T14:18:46Z

Uploaded a new patch that addresses @nikic feedback.

github-actions · 2024-01-09T14:20:30Z

✅ With the latest revision this PR passed the C/C++ code formatter.

CarlosAlbertoEnciso · 2024-01-09T14:48:35Z

Uploaded patch fixing the C/C++ code formatter, clang-format found issues.

jmorse

For the change adding the "ExitBlock" field to the RewritePhi struct -- as far as understand it, the PHI being rewritten is always going to be in that exit block. Perhaps we could not store it in the struct and instead recover the exit block by calling getParent() on the PHI when necessary, instead? (This avoids two storing two pieces of information and having to think about whether they're in sync or not).

jmorse · 2024-01-12T18:46:39Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

      PN->replaceAllUsesWith(ExitVal);
      PN->eraseFromParent();
    }
  }

+  // If there are no PHIs to be rewritten then there are no loop live-out
+  // values, try to rewrite variables corresponding to the induction variable


I reckon you want to say "rewrite debug variables" or similar, just to signal to the reader that these aren't for SSA variables which might have a functional effect on the program.

jmorse · 2024-01-12T18:47:38Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+  // will completely forget that this loop happened.
+  if (RewritePhiSet.empty()) {
+    // The loop exit value has been updated; insert the debug location
+    // for the given the induction variable with its final value.


"for the given induction..."

CarlosAlbertoEnciso · 2024-01-16T12:50:21Z

For the change adding the "ExitBlock" field to the RewritePhi struct -- as far as understand it, the PHI being rewritten is always going to be in that exit block. Perhaps we could not store it in the struct and instead recover the exit block by calling getParent() on the PHI when necessary, instead? (This avoids two storing two pieces of information and having to think about whether they're in sync or not).

Good point. Removed the added field.

@jmorse

https://bugs.llvm.org/show_bug.cgi?id=51735 llvm#51077 After internal discussion with @jmorse, it was decided to split the work between the 'indvars' and the 'loop-deletion' passes. 1) passes="loop(indvars)" - 'indvars' transformation is fired: the 'rewriteLoopExitValues' will rewrite the collected PNs with the exit values. - 'indvars' transformation is not fired: If the loop can be deleted, we preserve the induction variable information to be used by 'loop-deletion' if that pass will be executed. 2) passes="loop(indvars,loop-deletion)" If the loop is deleted in 'deleteDeadLoop' and there is a valid exit block, we use any collected values by 'indvars' to updated the exit values. Added extra tests to cover the following cases: ... char Var = 1; for (; Index < End; ++Index) if (Index == 666) ++Var; ... and ... char Var = 1; for (; Index < End; ++Index) if (Index == 666) Var = 555; ... Modified but otherwise unused variable 'Var' in a loop that gets deleted.

SLTozer

Largely looks good, some comments inline.

SLTozer · 2024-03-14T14:08:49Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+      SmallVector<WeakVH> &DbgUsers = L->getDebugInductionVariableDebugUsers();
+      for (WeakVH &DebugUser : DbgUsers)
+        if (DebugUser)
+          dyn_cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(


Suggested change

dyn_cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(

cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(

This should just be a normal cast - the idea of dyn_cast is that it can return nullptr if the cast is unsuccessful, unlike cast which just asserts; if you aren't checking the result for nullptr, then there's no value in using dyn_cast over cast. I think in this case, you just want cast, since the check above already verifies that the value has not been deleted.

Thanks for the additional information on dyn_cast. Changed to cast.

SLTozer · 2024-03-15T16:22:28Z

llvm/test/Transforms/IndVarSimplify/pr51735-2.ll

+; PRE-CHECK:   br label %for.cond
+
+; PRE-CHECK: for.end:
+; PRE-CHECK-NOT: call void @llvm.dbg.value


This can be skipped since there's an implicit-check-not.

SLTozer · 2024-03-15T16:28:50Z

llvm/test/Transforms/IndVarSimplify/pr51735-2.ll

+
+; Only the 'indvars' pass is executed.
+; PRE-CHECK: for.cond:
+; PRE-CHECK:   call void @llvm.dbg.value(metadata i32 %Var.0, metadata ![[DBG]], {{.*}}


This and a lot of the other check lines may fail in a build without assertions enabled, as the SSA values won't necessarily be printed with the same names (they may become numbered values, e.g. %5, %6, etc). Usually the way to test these would then be to use capture variables for them, e.g. i32 %[[SSA_VAR0:.+]],. This gets tedious if you have to use it for every variable, so I'd recommend removing the unrelated CHECK lines, which would be most of the lines that don't need to be tested for and don't produce a value that we want to check; or instead of removing them, you could cut out actual SSA values, i.e. you could just test for = icmp eq.

Thanks for the additional information. Changed to use captured variables.

SLTozer · 2024-03-15T16:33:09Z

llvm/lib/Transforms/Utils/LoopUtils.cpp

+      continue;
+    auto *Cloned = cast<DbgVariableIntrinsic>(DebugUser->clone());
+    Cloned->replaceVariableLocationOp(0u, PN);
+    Cloned->insertBefore(Successor->getFirstNonPHI());


We should fix this up for the new insert logic (same in the function below):

Suggested change

Cloned->insertBefore(Successor->getFirstNonPHI());

Cloned->insertBefore(Successor, Successor->getFirstNonPHIIt());

Changed to use new insert logic.

@SLTozer

https://bugs.llvm.org/show_bug.cgi?id=51735 llvm#51077 Address @SLTozer comments. - Use captured variables for SSA values. - Use new insert logic calls. - Remove not required 'CHECK-NOT'.

CarlosAlbertoEnciso · 2024-03-18T08:17:47Z

@SLTozer Thanks for your comments. Updated the patch.

SLTozer · 2024-03-18T10:05:28Z

One more part - you've captured the SSA values that are needed for the test, but for the SSA values you're not using you should still remove the actual names so that if the identifiers change (which can happen when building with assertions ~~enabled~~ disabled I think) the test doesn't fail. Since you don't need to use the captured names, you can just use {{.+}}, or else you can just omit some of the lines in whole or in part.

@SLTozer

https://bugs.llvm.org/show_bug.cgi?id=51735 llvm#51077 Address @SLTozer comments. - Don't use any names for not used SSA values.

CarlosAlbertoEnciso · 2024-03-19T13:59:48Z

@SLTozer Thanks for the suggested changes when dealing with the not used SSA values.

CarlosAlbertoEnciso · 2024-04-03T11:19:50Z

Any additional comments or suggestions? Thanks.

CarlosAlbertoEnciso · 2024-04-08T04:32:29Z

Thanks to all reviewers for their comments.

nikic · 2024-04-08T05:22:58Z

This introduces a layering violation. GenericLoopInfo in Support is not allowed to depend on IR. That's the point of the GenericXYZ implementations, they are IR-agnostic.

Edit: Reverted in 91189af.

nikic · 2024-04-08T05:24:46Z

llvm/include/llvm/Support/GenericLoopInfo.h

+  // there are no PHIs to be rewritten.
+  // For now, we only preserve single induction variables.
+  Value *IndVarFinalValue = nullptr;
+  SmallVector<WeakVH> IndVarDebugUsers;


Why is it necessary for these to be members on the Loop object itself?

It also introduced some link errors. Reverting the patch.

Thanks for reverting. I will look at that layering violation.

This reverts commit 739fa1c. This introduces a layering violation by using IR in Support headers.

CarlosAlbertoEnciso · 2024-04-10T13:51:19Z

Reopen as #88270 to address @nikic comments.

CarlosAlbertoEnciso added debuginfo llvm:transforms labels Oct 23, 2023

CarlosAlbertoEnciso requested review from nikic, jryans, jmorse, adrian-prantl, SLTozer, felipepiovezan, OCHyams, dwblaikie, pogo59 and djtodoro October 23, 2023 12:23

CarlosAlbertoEnciso self-assigned this Oct 23, 2023

nikic reviewed Oct 23, 2023

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CarlosAlbertoEnciso force-pushed the pr-51077 branch from 3a32bec to 276fcc7 Compare October 26, 2023 06:46

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CarlosAlbertoEnciso force-pushed the pr-51077 branch from 276fcc7 to 9cad349 Compare January 3, 2024 12:11

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CarlosAlbertoEnciso force-pushed the pr-51077 branch 2 times, most recently from 74d48ef to 88f7d8c Compare January 9, 2024 14:17

CarlosAlbertoEnciso force-pushed the pr-51077 branch from 88f7d8c to 0270560 Compare January 9, 2024 14:47

jmorse reviewed Jan 12, 2024

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CarlosAlbertoEnciso requested review from aaupov, maksfb, rafaelauler, ayermolo, dcci and Endilll as code owners March 13, 2024 17:50

CarlosAlbertoEnciso force-pushed the pr-51077 branch from 04fa787 to 0427224 Compare March 13, 2024 17:57

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[indvars] Missing variables at Og:

ac8a3aa

https://bugs.llvm.org/show_bug.cgi?id=51735 llvm#51077 Address @SLTozer comments. - Use captured variables for SSA values. - Use new insert logic calls. - Remove not required 'CHECK-NOT'.

[indvars] Missing variables at Og:

9e4c629

https://bugs.llvm.org/show_bug.cgi?id=51735 llvm#51077 Address @SLTozer comments. - Don't use any names for not used SSA values.

SLTozer approved these changes Mar 19, 2024

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CarlosAlbertoEnciso merged commit 739fa1c into llvm:main Apr 8, 2024
4 checks passed

nikic reviewed Apr 8, 2024

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nikic added a commit that referenced this pull request Apr 8, 2024

Revert "[indvars] Missing variables at Og: (#69920)"

91189af

This reverts commit 739fa1c. This introduces a layering violation by using IR in Support headers.

CarlosAlbertoEnciso mentioned this pull request Apr 17, 2024

[indvars] Missing variables at Og #88270

Merged

	dyn_cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(
	cast<DbgVariableIntrinsic>(DebugUser)->replaceVariableLocationOp(

	Cloned->insertBefore(Successor->getFirstNonPHI());
	Cloned->insertBefore(Successor, Successor->getFirstNonPHIIt());

[indvars] Missing variables at Og: #69920

[indvars] Missing variables at Og: #69920

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