[clang] [compiler-rt] Fix "[clang][UBSan] Add implicit conversion check for bitfields" (PR #87761)

[Michael Halkenhäuser via cfe-commits]

================
@@ -0,0 +1,94 @@
+// RUN: %clang -x c++ -fsanitize=implicit-bitfield-conversion -target x86_64-linux -S -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,CHECK-BITFIELD-CONVERSION
+// RUN: %clang -x c++ -fsanitize=implicit-integer-conversion -target x86_64-linux -S -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK
+// RUN: %clang -x c++ -fsanitize=implicit-conversion -target x86_64-linux -S -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,CHECK-BITFIELD-CONVERSION
+
+struct S {
+  int a:3;
+  char b:2;
+};
+
+class C : public S {
+  public:
+    short c:3;
+};
+
+S s;
+C c;
+
+// CHECK-LABEL: define{{.*}} void @{{.*foo1.*}}
+void foo1(int x) {
+  s.a = x;
+  // CHECK: store i8 %{{.*}}
+  // CHECK-BITFIELD-CONVERSION: [[BFRESULTSHL:%.*]] = shl i8 {{.*}}, 5
+  // CHECK-BITFIELD-CONVERSION-NEXT: [[BFRESULTASHR:%.*]] = ashr i8 [[BFRESULTSHL]], 5
+  // CHECK-BITFIELD-CONVERSION-NEXT: [[BFRESULTCAST:%.*]] = sext i8 [[BFRESULTASHR]] to i32
+  // CHECK-BITFIELD-CONVERSION: call void @__ubsan_handle_implicit_conversion
+  // CHECK-BITFIELD-CONVERSION-NEXT: br label %[[CONT:.*]], !nosanitize !6
----------------
mhalk wrote:

@Zonotora
**Q1: Is checking `!nosanitize` necessary?**
**Q2: Is checking `!6` necessary?**

Regarding the metadata, it's not always `!6` (at leat for us).
So, if we could simply remove at least this metadata check `!6` (or even both, if possible), it would probably solve the `check-clang` failures we are encountering.
Also, when looking at the output, the referred metadata is empty, in my case it was `!4`, with `!4 = !{}`.

https://github.com/llvm/llvm-project/pull/87761