[BoundsSan] Update BoundsChecking.cpp to use no-merge attribute where applicable (#120620)

#65972 introduced
-ubsan-unique-traps and -bounds-checking-unique-traps, which attach the
function size to the ubsantrap intrinsic.

#117651 changed
ubsan-unique-traps to use nomerge instead of the function size, but did
not update -bounds-checking-unique-traps. This patch adds nomerge to
bounds-checking-unique-traps.

Author: thurstond

clang/test/CodeGen/bounds-checking.c

@@ -85,11 +85,11 @@ char B2[10];
 // NOOPTLOCAL-LABEL: @f8
 // NOOPTARRAY-LABEL: @f8
 void f8(int i, int k) {
-  // NOOPTLOCAL: call void @llvm.ubsantrap(i8 3)
+  // NOOPTLOCAL: call void @llvm.ubsantrap(i8 3) #[[ATTR1:[0-9]+]]
   // NOOPTARRAY: call void @llvm.ubsantrap(i8 18) #[[ATTR2:[0-9]+]]
   B[i] = '\0';
 
-  // NOOPTLOCAL: call void @llvm.ubsantrap(i8 5)
+  // NOOPTLOCAL: call void @llvm.ubsantrap(i8 5) #[[ATTR1:[0-9]+]]
   // NOOPTARRAY: call void @llvm.ubsantrap(i8 18) #[[ATTR2:[0-9]+]]
   B2[k] = '\0';
 }
@@ -102,4 +102,5 @@ struct S {
 struct S *f9(int i) {
   return &s[i];
 }
+// NOOPTLOCAL: attributes #[[ATTR1]] = { nomerge noreturn nounwind }
 // NOOPTARRAY: attributes #[[ATTR2]] = { nomerge noreturn nounwind }

llvm/lib/Transforms/Instrumentation/BoundsChecking.cpp

@@ -196,8 +196,10 @@ static bool addBoundsChecking(Function &F, TargetLibraryInfo &TLI,
 
     CallInst *TrapCall;
     if (DebugTrapBB) {
+      // Ideally we would use the SanitizerHandler::OutOfBounds constant
       TrapCall = IRB.CreateIntrinsic(
           IntrID, {}, ConstantInt::get(IRB.getInt8Ty(), Fn->size()));
+      TrapCall->addFnAttr(llvm::Attribute::NoMerge);
     } else {
       TrapCall = IRB.CreateIntrinsic(IntrID, {}, {});
     }
@@ -251,4 +253,4 @@ void BoundsCheckingPass::printPipeline(
     OS << "<rt-abort>";
     break;
   }
-}
+}