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

[Jeremy Morse via cfe-commits]

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@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 %s -O0 -emit-llvm -fextend-this-ptr -o -  | FileCheck %s \
+// RUN:      --implicit-check-not="call void (...) @llvm.fake.use"
+// RUN: %clang_cc1 %s -O0 -emit-llvm -fextend-lifetimes -o - | FileCheck %s \
+// RUN:      --implicit-check-not="call void (...) @llvm.fake.use"
+// RUN: %clang_cc1 %s -O1 -emit-llvm -fextend-this-ptr -o -  | FileCheck -check-prefix=OPT %s
+// RUN: %clang_cc1 %s -O1 -emit-llvm -fextend-lifetimes -o - | FileCheck -check-prefix=OPT %s
+// RUN: %clang_cc1 %s -Os -emit-llvm -fextend-this-ptr -o -  | FileCheck -check-prefix=OPT %s
+// RUN: %clang_cc1 %s -Os -emit-llvm -fextend-lifetimes -o - | FileCheck -check-prefix=OPT %s
+// RUN: %clang_cc1 %s -Oz -emit-llvm -fextend-this-ptr -o -  | FileCheck -check-prefix=OPT %s
+// RUN: %clang_cc1 %s -Oz -emit-llvm -fextend-lifetimes -o - | FileCheck -check-prefix=OPT %s
+// Check that we do not generate a fake_use call when we are not optimizing. 
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jmorse wrote:

I reckon these can all be given `--disable-llvm-passes` too, as what we're checking is the effect of the optimisation flag on clang, not on the actual pipeline.

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