[Clang] Fix nomerge attribute not working with __builtin_trap(), __debugbreak(), __builtin_verbose_trap() (#101549)

1. It fixes the problem that llvm.trap() not getting the nomerge
attribute.
2. It sets nomerge flag for the node if the instruction has nomerge
arrtibute.

This is a copy of https://reviews.llvm.org/D146164. This only attempts
to fix `nomerge` for `__builtin_trap()`, `__debugbreak()`,
`__builtin_verbose_trap()`, not working for non-trap builtins.

Fixes #53011

Author: ZequanWu

clang/lib/CodeGen/CGExpr.cpp

@@ -3882,6 +3882,8 @@ llvm::CallInst *CodeGenFunction::EmitTrapCall(llvm::Intrinsic::ID IntrID) {
     TrapCall->addFnAttr(A);
   }
 
+  if (InNoMergeAttributedStmt)
+    TrapCall->addFnAttr(llvm::Attribute::NoMerge);
   return TrapCall;
 }
 

clang/test/CodeGen/attr-nomerge.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -emit-llvm %s -triple x86_64-unknown-linux-gnu -o - | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm %s -fms-extensions -o - | FileCheck %s
 
 class A {
 public:
@@ -42,6 +42,9 @@ void foo(int i, A *ap, B *bp) {
 
   A *newA = new B();
   delete newA;
+  [[clang::nomerge]] __builtin_trap();
+  [[clang::nomerge]] __debugbreak();
+  [[clang::nomerge]] __builtin_verbose_trap("check null", "Argument must not be null.");
 }
 
 int g(int i);
@@ -97,6 +100,9 @@ void something_else_again() {
 // CHECK: load ptr, ptr
 // CHECK: %[[AG:.*]] = load ptr, ptr
 // CHECK-NEXT: call void %[[AG]](ptr {{.*}}) #[[ATTR1]]
+// CHECK: call void @llvm.trap() #[[ATTR0]]
+// CHECK: call void @llvm.debugtrap() #[[ATTR0]]
+// CHECK: call void @llvm.trap() #[[ATTR0]]
 // CHECK: call void  @_ZN1AD1Ev(ptr {{.*}}) #[[ATTR1]]
 
 // CHECK-DAG: attributes #[[ATTR0]] = {{{.*}}nomerge{{.*}}}

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7448,6 +7448,8 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
         break;
       default: llvm_unreachable("unknown trap intrinsic");
       }
+      DAG.addNoMergeSiteInfo(DAG.getRoot().getNode(),
+                             I.hasFnAttr(Attribute::NoMerge));
       return;
     }
     TargetLowering::ArgListTy Args;
@@ -7464,7 +7466,7 @@ void SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I,
         DAG.getExternalSymbol(TrapFuncName.data(),
                               TLI.getPointerTy(DAG.getDataLayout())),
         std::move(Args));
-
+    CLI.NoMerge = I.hasFnAttr(Attribute::NoMerge);
     std::pair<SDValue, SDValue> Result = TLI.LowerCallTo(CLI);
     DAG.setRoot(Result.second);
     return;

llvm/test/CodeGen/X86/nomerge.ll

@@ -62,4 +62,96 @@ if.end:
 
 declare dso_local void @bar()
 
+define void @nomerge_trap(i32 %i) {
+; CHECK-LABEL: nomerge_trap:
+; CHECK:      # %bb.0: # %entry
+; CHECK:      # %bb.1: # %entry
+; CHECK:      # %bb.2: # %if.then
+; CHECK-NEXT: ud2
+; CHECK-NEXT: LBB1_3: # %if.then2
+; CHECK-NEXT: ud2
+; CHECK-NEXT: .LBB1_4: # %if.end3
+; CHECK-NEXT: ud2
+entry:
+  switch i32 %i, label %if.end3 [
+    i32 5, label %if.then
+    i32 7, label %if.then2
+  ]
+
+if.then:
+  tail call void @llvm.trap() #0
+  unreachable
+
+if.then2:
+  tail call void @llvm.trap() #0
+  unreachable
+
+if.end3:
+  tail call void @llvm.trap() #0
+  unreachable
+}
+
+declare dso_local void @llvm.trap()
+
+define void @nomerge_debugtrap(i32 %i) {
+; CHECK-LABEL: nomerge_debugtrap:
+; CHECK:      # %bb.0: # %entry
+; CHECK:      # %bb.1: # %entry
+; CHECK:      # %bb.2: # %if.then
+; CHECK-NEXT: int3
+; CHECK-NEXT: LBB2_3: # %if.then2
+; CHECK-NEXT: int3
+; CHECK-NEXT: .LBB2_4: # %if.end3
+; CHECK-NEXT: int3
+entry:
+  switch i32 %i, label %if.end3 [
+    i32 5, label %if.then
+    i32 7, label %if.then2
+  ]
+
+if.then:
+  tail call void @llvm.debugtrap() #0
+  unreachable
+
+if.then2:
+  tail call void @llvm.debugtrap() #0
+  unreachable
+
+if.end3:
+  tail call void @llvm.debugtrap() #0
+  unreachable
+}
+
+define void @nomerge_named_debugtrap(i32 %i) {
+; CHECK-LABEL: nomerge_named_debugtrap:
+; CHECK:      # %bb.0: # %entry
+; CHECK:      # %bb.1: # %entry
+; CHECK:      # %bb.2: # %if.then
+; CHECK-NEXT: callq trap_func@PLT
+; CHECK-NEXT: LBB3_3: # %if.then2
+; CHECK-NEXT: callq trap_func@PLT
+; CHECK-NEXT: .LBB3_4: # %if.end3
+; CHECK-NEXT: callq trap_func@PLT
+entry:
+  switch i32 %i, label %if.end3 [
+    i32 5, label %if.then
+    i32 7, label %if.then2
+  ]
+
+if.then:
+  tail call void @llvm.debugtrap() #1
+  unreachable
+
+if.then2:
+  tail call void @llvm.debugtrap() #1
+  unreachable
+
+if.end3:
+  tail call void @llvm.debugtrap() #1
+  unreachable
+}
+
+declare dso_local void @llvm.debugtrap()
+
 attributes #0 = { nomerge }
+attributes #1 = { nomerge "trap-func-name"="trap_func" }