[clang] [Clang] Add fake use emission to Clang with -fextend-lifetimes (PR #110102)

[Jeremy Morse via cfe-commits]

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@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 %s -O1 -emit-llvm -fextend-lifetimes -fsanitize=null -fsanitize-trap=null -o - | FileCheck --check-prefix TRAP %s
+// RUN: %clang_cc1 %s -O1 -emit-llvm -fextend-lifetimes -o - | FileCheck --check-prefix FAKEUSE %s
+
+// With -fextend-lifetimes the compiler generated a fake.use of a
+// reference variable at the end of the function, in the cleanup block. This prompted the 
+// address sanitizer to verify that the variable has been allocated properly, even when 
+// the function returns early.
+// We check that sanitizers are disabled for code generated for the benefit of fake.use 
+// intrinsics, as well as that the fake.use is no longer generated in the cleanup block.
+// It should be generated in the block preceding the cleanup block instead.
+
+struct A { short s1, s2; };
+extern A& getA();
+
+void foo()
+{
+  auto& va = getA();
+  short s = va.s1 & ~va.s2;
+  if (s == 0)
+    return;
+
+  auto& vb = getA();
+}
+
+// TRAP:         define{{.*}}foo
+// TRAP:         [[COMPARE:%[^\s]*]] = icmp eq
+// TRAP-NOT:     br i1 [[COMPARE]]{{.*}}trap
+// TRAP:         br i1 [[COMPARE]]{{.*}}%if.end
+// TRAP-NOT:     trap:
+// TRAP:         if.end:
+// TRAP-NOT:     call{{.*}}llvm.trap
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jmorse wrote:

Exactly what's being tested for here isn't clear: seemingly that there are no trap calls / blocks in the function? It might be easier to use implicit-check-not for "trap", and explicitly check for the overall control-flow of the function.

https://github.com/llvm/llvm-project/pull/110102