[Clang] Implement P2809: Trivial infinite loops are not Undefined Behavior (#90066)

https://wg21.link/P2809R3

This is applied as a DR to C++11 (C++98 did not guarantee forward
progress and is left untouched)

As an extension (and to preserve existing behavior in C), we consider
all controlling expression that can be constant folded
in the front end, not just standard constant expressions.

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 87766a7..546beae 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1471,6 +1471,8 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
 
   // Ensure that the function adheres to the forward progress guarantee, which
   // is required by certain optimizations.
+  // In C++11 and up, the attribute will be removed if the body contains a
+  // trivial empty loop.
   if (checkIfFunctionMustProgress())
     CurFn->addFnAttr(llvm::Attribute::MustProgress);