LukeZhuang added inline comments.
================
Comment at: clang/lib/CodeGen/CGBuiltin.cpp:2195
+ Value *ExpectedValue = EmitScalarExpr(E->getArg(1));
+ Value *Confidence = EmitScalarExpr(E->getArg(2));
+ // Don't generate llvm.expect.with.probability on -O0 as the backend
----------------
rsmith wrote:
> If the intrinsic expects a `ConstantFP` value, this isn't enough to guarantee
> that you get one (the set of cases that we fold to constants during
> expression emission is much smaller than the set of cases we can
> constant-evaluate). You should run the constant evaluator first, to produce
> an `APFloat`, then emit that value as a constant. (Optionally you can form a
> `ConstantExpr` as part of the check in `Sema` and store the value in that
> object rather than recomputing it here.)
Thank you for commenting! I have a question about this. If I check this
argument can be fold as constant float in `Sema`, why I need to check it here?
Or do you mean I had better create a `ConstantFP` value here after constant
emitting?
================
Comment at: clang/lib/Sema/SemaChecking.cpp:1805
+ const Expr *ProbArg = TheCall->getArg(2);
+ if (ProbArg->EvaluateAsFloat(Confidence, Context)) {
+ double P = Confidence.convertToDouble();
----------------
rsmith wrote:
> What rules should be applied here? Do we just want to allow anything that we
> can evaluate (which might change over time), or do we want to use the
> underlying language's notion of floating-point constant expressions, if it
> has them?
Thank you for commenting. I just read the llvm::Expr document and found that it
just have `isIntegerConstantExpr` without a float-point version. Under
`EvaluateAsFloat` it says "Return true if this is a constant which we can fold
and convert to a floating point value", thus I use this function. Is there any
better function to achieve this goal?
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D79830/new/
https://reviews.llvm.org/D79830
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