================
@@ -12367,8 +12368,17 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const
CallExpr *E,
BuiltinOp != Builtin::BI__lzcnt &&
BuiltinOp != Builtin::BI__lzcnt64;
- if (ZeroIsUndefined && !Val)
- return Error(E);
+ if (!Val) {
----------------
nickdesaulniers wrote:
https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005fclzg
> Similar to __builtin_clz, except the argument is type-generic unsigned
> integer (standard, extended or bit-precise) and there is optional second
> argument with int type. No integral argument promotions are performed on the
> first argument. If two arguments are specified, and first argument is 0, the
> result is the second argument. If only one argument is specified and it is 0,
> the result is undefined.
The code as written is doing:
1. evaluate arg 0.
2. if evaluation is 0 and the builtin is clzg and num args > 1
3. evaluate arg 1
Consider that it may be cheaper to evaluate the number of args than the full
subexpression (at least when the sub expression itself is more than just a
literal iteger).
The code can be rewritten as:
```suggestion
case Builtin::BI__builtin_clzg:
case Builtin::BI__builtin_ctzg: {
unsigned ArgToEval = E->getNumArgs() > 1 ? 1 : 0;
APSInt Val;
if (!EvaluateInteger(E->getArg(0), Val, Info))
return false;
if (E->getNumArgs() == 1 && !Val)
return Error(E);
return Success(...
```
https://github.com/llvm/llvm-project/pull/86577
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