JIT: Remove unneeded unconditional jumps (#69041)

* resolve merge conflict

* add checks for post-call jmp removal

* use emitIsLastInsCall() to preclude call,jmp pairs and simplfy emitRemoveJumpToNextInst
check for aligned instruction groups and skip them to preserve alignment
linearize emitRemoveJumpToNextInst, add safety asserts for ordering and comment the requirement, add debug output explaining decisions

* address feedback

* change instruction omit to use code size zero

* address feedback

* add assertion info dump

* address feedback

* address feedback

* remove end loop cleanup. cleanup jitdump messages and add early out flag.

* address feedback, formatting

* update variable naming and clarify comments

* more feedback

* add last instruction check and group flag set in emitSavIG

* more feedback

* fix jitdump output and make removal candidate printing optional

* remove emitDispJumpList parameter

* change overall size calculation and allow 0 size align to be printed in dumps

* fix invorrect jmp check, remove inline for emitInstHasNoCode

* allow alignment printing even when zero

* remove debug printf and fix x86

* address feedback

src/coreclr/jit/codegen.h

@@ -1472,8 +1472,11 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 
 public:
     void instGen(instruction ins);
-
+#if defined(TARGET_XARCH)
+    void inst_JMP(emitJumpKind jmp, BasicBlock* tgtBlock, bool isRemovableJmpCandidate = false);
+#else
     void inst_JMP(emitJumpKind jmp, BasicBlock* tgtBlock);
+#endif
 
     void inst_SET(emitJumpKind condition, regNumber reg);
 

src/coreclr/jit/codegenarmarch.cpp

@@ -4288,6 +4288,18 @@ void CodeGen::inst_SETCC(GenCondition condition, var_types type, regNumber dstRe
 #endif
 }
 
+//------------------------------------------------------------------------
+// inst_JMP: Generate a jump instruction.
+//
+void CodeGen::inst_JMP(emitJumpKind jmp, BasicBlock* tgtBlock)
+{
+#if !FEATURE_FIXED_OUT_ARGS
+    assert((tgtBlock->bbTgtStkDepth * sizeof(int) == genStackLevel) || isFramePointerUsed());
+#endif // !FEATURE_FIXED_OUT_ARGS
+
+    GetEmitter()->emitIns_J(emitter::emitJumpKindToIns(jmp), tgtBlock);
+}
+
 //------------------------------------------------------------------------
 // genCodeForStoreBlk: Produce code for a GT_STORE_OBJ/GT_STORE_DYN_BLK/GT_STORE_BLK node.
 //

src/coreclr/jit/codegencommon.cpp

@@ -1944,11 +1944,12 @@ void CodeGen::genGenerateMachineCode()
 #endif // DEBUG
 
     /* We can now generate the function prolog and epilog */
-
     genGeneratePrologsAndEpilogs();
 
-    /* Bind jump distances */
+    // check to see if any jumps can be removed
+    GetEmitter()->emitRemoveJumpToNextInst();
 
+    /* Bind jump distances */
     GetEmitter()->emitJumpDistBind();
 
 #if FEATURE_LOOP_ALIGN

src/coreclr/jit/codegenlinear.cpp

@@ -753,7 +753,24 @@ void CodeGen::genCodeForBBlist()
                 break;
 
             case BBJ_ALWAYS:
-                inst_JMP(EJ_jmp, block->bbJumpDest);
+                inst_JMP(EJ_jmp, block->bbJumpDest
+#ifdef TARGET_AMD64
+                         // AMD64 requires an instruction after a call instruction for unwinding
+                         // inside an EH region so if the last instruction generated was a call instruction
+                         // do not allow this jump to be marked for possible later removal.
+                         //
+                         // If a block was selected to place an alignment instruction because it ended
+                         // with a jump, do not remove jumps from such blocks.
+                         ,
+                         /* isRemovableJmpCandidate */ !GetEmitter()->emitIsLastInsCall() && !block->hasAlign()
+#else
+#ifdef TARGET_XARCH
+                         ,
+                         /* isRemovableJmpCandidate */ !block->hasAlign()
+#endif
+
+#endif
+                             );
                 FALLTHROUGH;
 
             case BBJ_COND:

src/coreclr/jit/codegenxarch.cpp

@@ -1436,6 +1436,30 @@ void CodeGen::inst_SETCC(GenCondition condition, var_types type, regNumber dstRe
     }
 }
 
+//------------------------------------------------------------------------
+// inst_JMP: Generate a jump instruction.
+//
+void CodeGen::inst_JMP(emitJumpKind jmp, BasicBlock* tgtBlock, bool isRemovableJmpCandidate)
+{
+#if !FEATURE_FIXED_OUT_ARGS
+    // On the x86 we are pushing (and changing the stack level), but on x64 and other archs we have
+    // a fixed outgoing args area that we store into and we never change the stack level when calling methods.
+    //
+    // Thus only on x86 do we need to assert that the stack level at the target block matches the current stack level.
+    //
+    CLANG_FORMAT_COMMENT_ANCHOR;
+
+#ifdef UNIX_X86_ABI
+    // bbTgtStkDepth is a (pure) argument count (stack alignment padding should be excluded).
+    assert((tgtBlock->bbTgtStkDepth * sizeof(int) == (genStackLevel - curNestedAlignment)) || isFramePointerUsed());
+#else
+    assert((tgtBlock->bbTgtStkDepth * sizeof(int) == genStackLevel) || isFramePointerUsed());
+#endif
+#endif // !FEATURE_FIXED_OUT_ARGS
+
+    GetEmitter()->emitIns_J(emitter::emitJumpKindToIns(jmp), tgtBlock, 0, isRemovableJmpCandidate);
+}
+
 //------------------------------------------------------------------------
 // genCodeForReturnTrap: Produce code for a GT_RETURNTRAP node.
 //