Improve __builtin_constant_p lowering

__builtin_constant_p used to be short-cut evaluated to false when
building with -O0. This is undesirable as it means that constant folding
in the front-end can give different results than folding in the back-end.
It can also create conditional branches on constant conditions that don't
get folded away. With the pending improvements to the llvm.is.constant
handling on the LLVM side, the short-cut is no longer useful.

Adjust various codegen tests to not depend on the short-cut or the
backend optimisations.

Differential Revision: https://reviews.llvm.org/D67638

llvm-svn: 374742

1 files changed, 0 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index ddff595987b..2ccd16da256 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -2101,10 +2101,6 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
 
   case Builtin::BI__builtin_constant_p: {
     llvm::Type *ResultType = ConvertType(E->getType());
-    if (CGM.getCodeGenOpts().OptimizationLevel == 0)
-      // At -O0, we don't perform inlining, so we don't need to delay the
-      // processing.
-      return RValue::get(ConstantInt::get(ResultType, 0));
 
     const Expr *Arg = E->getArg(0);
     QualType ArgType = Arg->getType();