From 5107ce194c9b03c2f32eb1508df0c92b13b3e2fd Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston@google.com>
Date: Tue, 26 Nov 2024 21:07:48 +0000
Subject: [PATCH] Don't apply nomerge for the first instance of each TrapBB
 type, per Vitaly's feedback

---
 clang/lib/CodeGen/CGExpr.cpp          | 4 +++-
 clang/test/CodeGen/ubsan-trap-merge.c | 5 +++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 74e185c30c08787..5b669a980ec3e7b 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -3915,6 +3915,7 @@ void CodeGenFunction::EmitTrapCheck(llvm::Value *Checked,
                               Builder.getCurrentDebugLocation());
     Builder.CreateCondBr(Checked, Cont, TrapBB);
   } else {
+    bool NewTrapBB = (TrapBB == nullptr);
     TrapBB = createBasicBlock("trap");
     Builder.CreateCondBr(Checked, Cont, TrapBB);
     EmitBlock(TrapBB);
@@ -3928,7 +3929,8 @@ void CodeGenFunction::EmitTrapCheck(llvm::Value *Checked,
                                     CGM.getCodeGenOpts().TrapFuncName);
       TrapCall->addFnAttr(A);
     }
-    TrapCall->addFnAttr(llvm::Attribute::NoMerge);
+    if (!NewTrapBB)
+        TrapCall->addFnAttr(llvm::Attribute::NoMerge);
     TrapCall->setDoesNotReturn();
     TrapCall->setDoesNotThrow();
     Builder.CreateUnreachable();
diff --git a/clang/test/CodeGen/ubsan-trap-merge.c b/clang/test/CodeGen/ubsan-trap-merge.c
index ef32605c73174ae..c8669b9dd3a0323 100644
--- a/clang/test/CodeGen/ubsan-trap-merge.c
+++ b/clang/test/CodeGen/ubsan-trap-merge.c
@@ -55,7 +55,7 @@ int g(int x) {
 // CHECK-NEXT:    [[TMP3:%.*]] = extractvalue { i32, i1 } [[TMP2]], 1, !nosanitize [[META2]]
 // CHECK-NEXT:    br i1 [[TMP3]], label %[[TRAP1:.*]], label %[[CONT2:.*]], !nosanitize [[META2]]
 // CHECK:       [[TRAP1]]:
-// CHECK-NEXT:    tail call void @llvm.ubsantrap(i8 0) #[[ATTR4]], !nosanitize [[META2]]
+// CHECK-NEXT:    tail call void @llvm.ubsantrap(i8 0) #[[ATTR5:[0-9]+]], !nosanitize [[META2]]
 // CHECK-NEXT:    unreachable, !nosanitize [[META2]]
 // CHECK:       [[CONT2]]:
 // CHECK-NEXT:    [[TMP4:%.*]] = extractvalue { i32, i1 } [[TMP2]], 0, !nosanitize [[META2]]
@@ -102,4 +102,5 @@ int m(int x, int y) {
   return f(x) + g(y);
 }
 //.
-// CHECK: attributes #[[ATTR4]] = { nomerge noreturn nounwind }
+// CHECK: attributes #[[ATTR4]] = { noreturn nounwind }
+// CHECK: attributes #[[ATTR5]] = { nomerge noreturn nounwind }