[CFE] Add nomerge function attribute to inline assembly.

Sometimes we also want to avoid merging inline assembly. This patch add
the nomerge function attribute to inline assembly.

Reviewed By: zequanwu

Differential Revision: https://reviews.llvm.org/D84225

Author: phoebewang

clang/lib/CodeGen/CGStmt.cpp

@@ -1954,12 +1954,16 @@ static llvm::MDNode *getAsmSrcLocInfo(const StringLiteral *Str,
 }
 
 static void UpdateAsmCallInst(llvm::CallBase &Result, bool HasSideEffect,
-                              bool ReadOnly, bool ReadNone, const AsmStmt &S,
+                              bool ReadOnly, bool ReadNone, bool NoMerge,
+                              const AsmStmt &S,
                               const std::vector<llvm::Type *> &ResultRegTypes,
                               CodeGenFunction &CGF,
                               std::vector<llvm::Value *> &RegResults) {
   Result.addAttribute(llvm::AttributeList::FunctionIndex,
                       llvm::Attribute::NoUnwind);
+  if (NoMerge)
+    Result.addAttribute(llvm::AttributeList::FunctionIndex,
+                        llvm::Attribute::NoMerge);
   // Attach readnone and readonly attributes.
   if (!HasSideEffect) {
     if (ReadNone)
@@ -2334,12 +2338,14 @@ void CodeGenFunction::EmitAsmStmt(const AsmStmt &S) {
         Builder.CreateCallBr(IA, Fallthrough, Transfer, Args);
     EmitBlock(Fallthrough);
     UpdateAsmCallInst(cast<llvm::CallBase>(*Result), HasSideEffect, ReadOnly,
-                      ReadNone, S, ResultRegTypes, *this, RegResults);
+                      ReadNone, InNoMergeAttributedStmt, S, ResultRegTypes,
+                      *this, RegResults);
   } else {
     llvm::CallInst *Result =
         Builder.CreateCall(IA, Args, getBundlesForFunclet(IA));
     UpdateAsmCallInst(cast<llvm::CallBase>(*Result), HasSideEffect, ReadOnly,
-                      ReadNone, S, ResultRegTypes, *this, RegResults);
+                      ReadNone, InNoMergeAttributedStmt, S, ResultRegTypes,
+                      *this, RegResults);
   }
 
   assert(RegResults.size() == ResultRegTypes.size());

clang/lib/Sema/SemaStmtAttr.cpp

@@ -183,6 +183,7 @@ class CallExprFinder : public ConstEvaluatedExprVisitor<CallExprFinder> {
   bool foundCallExpr() { return FoundCallExpr; }
 
   void VisitCallExpr(const CallExpr *E) { FoundCallExpr = true; }
+  void VisitAsmStmt(const AsmStmt *S) { FoundCallExpr = true; }
 
   void Visit(const Stmt *St) {
     if (!St)

clang/test/CodeGen/attr-nomerge.cpp

@@ -10,6 +10,7 @@ void foo(int i) {
   [[clang::nomerge]] f(bar(), bar());
   [[clang::nomerge]] [] { bar(); bar(); }(); // nomerge only applies to the anonymous function call
   [[clang::nomerge]] for (bar(); bar(); bar()) {}
+  [[clang::nomerge]] { asm("nop"); }
   bar();
 }
 // CHECK: call zeroext i1 @_Z3barv() #[[NOMERGEATTR:[0-9]+]]
@@ -22,5 +23,7 @@ void foo(int i) {
 // CHECK: call zeroext i1 @_Z3barv() #[[NOMERGEATTR]]
 // CHECK: call zeroext i1 @_Z3barv() #[[NOMERGEATTR]]
 // CHECK: call zeroext i1 @_Z3barv() #[[NOMERGEATTR]]
+// CHECK: call void asm {{.*}} #[[NOMERGEATTR2:[0-9]+]]
 // CHECK: call zeroext i1 @_Z3barv()
 // CHECK: attributes #[[NOMERGEATTR]] = { nomerge }
+// CHECK: attributes #[[NOMERGEATTR2]] = { nomerge nounwind }