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

[Jeremy Morse via cfe-commits]

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@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 %s -triple=%itanium_abi_triple -O1 -emit-llvm -fextend-lifetimes -o - | FileCheck %s
+// Make sure we don't crash compiling a lambda that is not nested in a function.
+// We also check that fake uses are properly issued in lambdas.
+
+int glob;
+
+extern int foo();
+
+struct S {
+  static const int a;
+};
+
+const int S::a = [](int b) __attribute__((noinline)) {
+  return b * foo();
+}
+(glob);
+
+int func(int param) {
+  return ([=](int lambdaparm) __attribute__((noinline))->int {
+    int lambdalocal = lambdaparm * 2;
+    return lambdalocal;
+  }(glob));
+}
+
+// We are looking for the first lambda's call operator, which should contain
+// 2 fake uses, one for 'b' and one for its 'this' pointer (in that order).
+// The mangled function name contains a $_0, followed by 'cl'.
+// This lambda is an orphaned lambda, i.e. one without lexical parent.
+//
+// CHECK:     define internal {{.+\"_Z.+\$_0.*cl.*\"}}
+// CHECK-NOT: ret
+// CHECK:     fake.use(i32
+// CHECK-NOT: ret
+// CHECK:     fake.use(ptr
+
+// The second lambda. We are looking for 3 fake uses.
+// CHECK:     define internal {{.+\"_Z.+\$_0.*cl.*\"}}
+// CHECK-NOT: ret
+// CHECK:     fake.use(i32
+// CHECK-NOT: ret
+// CHECK:     fake.use(i32
+// CHECK-NOT: ret
+// CHECK:     fake.use(ptr
----------------
jmorse wrote:

Any way to be more precise than "there are three fake uses", i.e. their specific locations? The firmer we are in testing, the fewer problems we'll have in the future.

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