Skip to content

[clang] Support constexpr bitcasts between equal-size vector and integer types #167016

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 1 commit into
base: main
Choose a base branch
from
Open

[clang] Support constexpr bitcasts between equal-size vector and integer types #167016

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 18 additions & 1 deletion clang/lib/AST/ExprConstant.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17078,7 +17078,24 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
case CK_HLSLAggregateSplatCast:
llvm_unreachable("invalid cast kind for integral value");

case CK_BitCast:
case CK_BitCast:{
APValue Sub;
if (!Evaluate(Sub, Info, E->getSubExpr()))
Copy link
Contributor

@tbaederr tbaederr Nov 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We know the types before evaluating the subexpression, so we don't have to do this unless the sizes match.

return false;

QualType SrcTy = E->getSubExpr()->getType();
QualType DstTy = E->getType();

// Allow reinterpretation if bit widths match
if (Info.Ctx.getTypeSize(SrcTy) == Info.Ctx.getTypeSize(DstTy)) {
// Use APValue::BitCast if available, else just copy value bits
Copy link
Contributor

@tbaederr tbaederr Nov 10, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

What is APValue::BitCast?

Result = Sub;
return true;
}

return Error(E);
}

case CK_Dependent:
case CK_LValueBitCast:
case CK_ARCProduceObject:
Expand Down
Loading