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

[Paul T Robinson via cfe-commits]

================
@@ -1353,6 +1353,19 @@ void CodeGenFunction::EmitLifetimeEnd(llvm::Value *Size, llvm::Value *Addr) {
   C->setDoesNotThrow();
 }
 
+void CodeGenFunction::EmitFakeUse(Address Addr) {
+  // We do not emit a fake use if we want to apply optnone to this function,
+  // even if we might not apply it anyway due to minsize or similar attributes.
+  if (!CGM.getCodeGenOpts().DisableO0ImplyOptNone &&
+      CGM.getCodeGenOpts().OptimizationLevel == 0)
+    return;
----------------
pogo59 wrote:

Objection withdrawn. Because it's opt-in, we should do what the user requested. As you say, in a normal `-O0` situation all this does is increase IR size for no benefit, but it has its uses.

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