[clang] [CIR] Upstream lowering of conditional operators to TernaryOp (PR #138156)

[Andy Kaylor via cfe-commits]

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@@ -1658,6 +1828,170 @@ mlir::Value ScalarExprEmitter::VisitUnaryExprOrTypeTraitExpr(
                cgf.cgm.UInt64Ty, e->EvaluateKnownConstInt(cgf.getContext())));
 }
 
+/// Return true if the specified expression is cheap enough and side-effect-free
+/// enough to evaluate unconditionally instead of conditionally.  This is used
+/// to convert control flow into selects in some cases.
+/// TODO(cir): can be shared with LLVM codegen.
+static bool isCheapEnoughToEvaluateUnconditionally(const Expr *e,
+                                                   CIRGenFunction &cgf) {
+  // Anything that is an integer or floating point constant is fine.
+  return e->IgnoreParens()->isEvaluatable(cgf.getContext());
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andykaylor wrote:

We wouldn't want to speculatively evaluate constant foldable floating point expressions if they might raise an exception. I don't think this handles that correctly. We are a long way from having strict floating-point semantics in CIR, but the classic codegen gets this wrong: https://godbolt.org/z/nvfT4WxK4

https://github.com/llvm/llvm-project/pull/138156