LukeZhuang added inline comments.
================
Comment at: clang/lib/CodeGen/CGBuiltin.cpp:2204
+ if (CGM.getCodeGenOpts().OptimizationLevel == 0)
+ return RValue::get(ArgValue);
+
----------------
erichkeane wrote:
> Do you still need to evaluate this for side-effects even when called with O1?
> I think this code only evaluates side-effects in O0 mode at the moment.
Hi, sorry I am not sure about it. Since this part of code is after evaluating
all three arguments(including evaluate `ProbArg` with allowing side effect), I
think it will evaluate `ProbArg` with side effect whatever the optimization
level is. This part of code is just early return the value of first argument
`ArgValue` and do not generate code to backend. Do I correctly understand this?
Thank you!
================
Comment at: clang/lib/Sema/SemaChecking.cpp:1805
+ const Expr *ProbArg = TheCall->getArg(2);
+ if (ProbArg->isValueDependent())
+ return ExprError();
----------------
erichkeane wrote:
> Why is value-dependent an error? The expression should be able to be a
> template parameter. For example:
>
>
> struct S {
> static constexpr float value = 1.1;
> };
>
> template<typename T>
> void f(bool b) {
> __builtin_expect_with_probability(b, 1, T::value);
> }
>
> should work.
>
> Additionally, in C++20(though not yet implemented in clang it seems):
>
> template<float F>
> void f(bool b) {
> __builtin_expect_with_probability(b, 1, F);
> }
>
> Additionally, how about an integer type? It would seem that I should be able
> ot do:
> template<int I>
> void f(bool b) {
> __builtin_expect_with_probability(b, 1, I); // probability is obviously 0
> or 1
> }
>
Hi, this code is based on Richard's suggestion that checking `ProbArg` is not
value-dependent before evaluate. I also saw `EvaluateAsFloat` source code used
in CGBuiltin.cpp that it firstly assert the expression is not value-dependent
as following:
```
bool Expr::EvaluateAsFloat(APFloat &Result, const ASTContext &Ctx,
SideEffectsKind AllowSideEffects,
bool InConstantContext) const {
assert(!isValueDependent() &&
"Expression evaluator can't be called on a dependent expression.");
```
In fact I am not sure is there anything special should be done when is
value-dependent. Do you have suggestions about this? Thank you!
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D79830/new/
https://reviews.llvm.org/D79830
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