Merge rust-lang#62

62: Add the yk-linkage llvm pass. r=ltratt a=vext01



Co-authored-by: Edd Barrett <vext01@gmail.com>

llvm/include/llvm/Transforms/Yk/Linkage.h

@@ -0,0 +1,10 @@
+#ifndef LLVM_TRANSFORMS_YK_LINKAGE_H
+#define LLVM_TRANSFORMS_YK_LINKAGE_H
+
+#include "llvm/Pass.h"
+
+namespace llvm {
+ModulePass *createYkLinkagePass();
+} // namespace llvm
+
+#endif

llvm/lib/CodeGen/TargetPassConfig.cpp

@@ -48,6 +48,7 @@
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Yk/BlockDisambiguate.h"
 #include "llvm/Transforms/Yk/ControlPoint.h"
+#include "llvm/Transforms/Yk/Linkage.h"
 #include "llvm/Transforms/Yk/ShadowStack.h"
 #include "llvm/Transforms/Yk/Stackmaps.h"
 #include <cassert>
@@ -265,6 +266,10 @@ static cl::opt<bool> YkPatchCtrlPoint("yk-patch-control-point", cl::init(false),
                                       cl::NotHidden,
                                       cl::desc("Patch yk_mt_control_point()"));
 
+static cl::opt<bool> YkLinkage("yk-linkage", cl::init(false),
+                                      cl::NotHidden,
+                                      cl::desc("Change functions with internal linkage to have external linkage"));
+
 static cl::opt<bool>
     YkShadowStack("yk-shadow-stack", cl::init(false), cl::NotHidden,
                   cl::desc("Use a shadow stack for stack values."));
@@ -1132,6 +1137,10 @@ bool TargetPassConfig::addISelPasses() {
     addPass(createYkControlPointPass());
   }
 
+  if (YkLinkage) {
+    addPass(createYkLinkagePass());
+  }
+
   if (YkInsertStackMaps) {
     addPass(createYkStackmapsPass());
   }

llvm/lib/Transforms/Yk/CMakeLists.txt

@@ -1,6 +1,7 @@
 add_llvm_component_library(LLVMYkPasses
   BlockDisambiguate.cpp
   ControlPoint.cpp
+  Linkage.cpp
   LivenessAnalysis.cpp
   StackMaps.cpp
   ShadowStack.cpp

llvm/lib/Transforms/Yk/Linkage.cpp

@@ -0,0 +1,56 @@
+//===- Linkage.cpp - Ajdust linkage for the Yk JIT -----------------===//
+//
+// The JIT relies upon the use of `dlsym()` at runtime in order to lookup any
+// given function from its virtual address. For this to work the symbols for
+// all functions must be in the dynamic symbol table.
+//
+// `yk-config` already provides the `--export-dynamic` flag in order to ensure
+// that all *externally visible* symbols make it in to the dynamic symbol table,
+// but that's not enough: functions marked for internal linkage (e.g. `static`
+// functions in C) will be missed.
+//
+// This pass walks the functions of a module and flips any with internal linkage
+// to external linkage.
+//
+// Note that whilst symbols with internal linkage can have the same name and be
+// distinct, this is not so for symbols with external linkage. That's OK for
+// us because Yk requires the use of LTO, and the LTO module merger will have
+// already mangled the names for us so that symbol clashes can't occur.
+
+#include "llvm/Transforms/Yk/Linkage.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+
+#define DEBUG_TYPE "yk-linkage"
+
+using namespace llvm;
+
+namespace llvm {
+void initializeYkLinkagePass(PassRegistry &);
+} // namespace llvm
+
+namespace {
+class YkLinkage : public ModulePass {
+public:
+  static char ID;
+  YkLinkage() : ModulePass(ID) {
+    initializeYkLinkagePass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnModule(Module &M) override {
+    for (Function &F : M) {
+      if (F.hasInternalLinkage()) {
+        F.setLinkage(GlobalVariable::ExternalLinkage);
+      }
+    }
+    return true;
+  }
+};
+} // namespace
+
+char YkLinkage::ID = 0;
+INITIALIZE_PASS(YkLinkage, DEBUG_TYPE, "yk-linkage", false, false)
+
+ModulePass *llvm::createYkLinkagePass() { return new YkLinkage(); }

llvm/test/Transforms/Yk/Linkage/YkLinkage.ll

@@ -0,0 +1,10 @@
+; Checks that the yk-linkage pass changes functions to have external linkage.
+;
+; RUN: llc --yk-linkage -o - < %s | FileCheck %s
+; RUN: llc -o - < %s | FileCheck --check-prefix CHECK-NOPASS %s
+
+; CHECK: .globl myfunc
+; CHECK-NOPASS-NOT: .globl myfunc
+define internal void @myfunc() noinline {
+	ret void
+}