Treat __sync_synchronize and asm("":::"memory") as stronger fences.

lib/CodeGen/CGStmt.cpp

Index: lib/CodeGen/CGStmt.cpp
diff --git a/lib/CodeGen/CGStmt.cpp b/lib/CodeGen/CGStmt.cpp
index 5e2ebe0d9cd4656e9278c6a172513dc09ed0d77f..02ef13058637643650b0d80cd9526c49abb3dd63 100644
--- a/lib/CodeGen/CGStmt.cpp
+++ b/lib/CodeGen/CGStmt.cpp
@@ -22,6 +22,7 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/NaClAsm.h" // @LOCALMOD

[eliben, 2013/08/07 18:06:25]

This is a problem for upstreaming, no?

From the other CL I see all this new module contains is:

bool isAsmMemory(const Instruction *I);

What makes this NaCl specific? Can't you just put this utility function in a
more generic place? If llvm/IR/InlineAsm.h is not suitable, maybe
llvm/IR/InlineAsmUtils.h or something? This would allow upstreaming and avoiding
a localmod in both Clang and LLVM

[JF, 2013/08/07 19:48:12]

Done.

 using namespace clang;
 using namespace CodeGen;
 
@@ -1701,6 +1702,18 @@ void CodeGenFunction::EmitAsmStmt(const AsmStmt &S) {
   Result->addAttribute(llvm::AttributeSet::FunctionIndex,
                        llvm::Attribute::NoUnwind);
 
+  // @LOCALMOD-START
+  if (getTargetHooks().asmMemoryIsFence() && llvm::NaCl::isAsmMemory(Result)) {

[eliben, 2013/08/07 18:06:25]

It's weird that you're going the generic way with target hooks and yet directly
query a NaCl:: function

[JF, 2013/08/07 19:48:12]

Done.

+    // Targets can ask that ``asm("":::"memory")`` be treated like
+    // ``__sync_synchronize()``.
+    Builder.CreateFence(llvm::SequentiallyConsistent);
+    Builder.CreateCall(
+        llvm::InlineAsm::get(FTy, AsmString, Constraints, HasSideEffect))->
+        addAttribute(llvm::AttributeSet::FunctionIndex,
+                     llvm::Attribute::NoUnwind);
+  }
+  // @LOCALMOD-END
+
   // Slap the source location of the inline asm into a !srcloc metadata on the
   // call.  FIXME: Handle metadata for MS-style inline asms.
   if (const GCCAsmStmt *gccAsmStmt = dyn_cast<GCCAsmStmt>(&S))