https://github.com/usx95 created
https://github.com/llvm/llvm-project/pull/108197
Consider when Input[I] is a VarDecl with parameter pack. We would have already
expanded the pack before the code change in the loop`for (unsigned I = 0; I !=
*NumExpansions; ++I) {`.
Now in `if (RetainExpansion) {`, without this change, we continue to substitute
the pack in the pattern even when we do not have meaningful
`ArgumentPackSubstitutionIndex` set.
This leads to use of an invalid pack substitution index in
`TemplateInstantiator::TransformFunctionParmPackRefExpr` containing
`TransformedDecl = (*Pack)[getSema().ArgumentPackSubstitutionIndex];`
This change set `ArgumentPackSubstitutionIndex` to `-1` while retaining
expansion to instruct `TransformFunctionParmPackRefExpr` to build
`FunctionParmPackExpr` instead of substituting the param pack.
---
There are other instances of `RetainExpansion` and IIUC, they should also unset
the `ArgumentPackSubstitutionIndex`. It would be great if someone can verify my
understanding. If this is correct then we could instead have a
`ArgumentPackSubstitutionIndexRAII` as part of
`ForgetPartiallySubstitutedPackRAII`.
Fixes https://github.com/llvm/llvm-project/issues/63819
>From 5901d82ea0543074853b963f7dc9106a6fe3bcee Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <[email protected]>
Date: Wed, 11 Sep 2024 11:33:45 +0000
Subject: [PATCH 1/2] [clang] Do not expand pack while retaining expansion
---
clang/lib/Sema/TreeTransform.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 0daf620b4123e4..a40673b04764da 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -4361,7 +4361,7 @@ bool TreeTransform<Derived>::TransformExprs(Expr *const
*Inputs,
// forgetting the partially-substituted parameter pack.
if (RetainExpansion) {
ForgetPartiallySubstitutedPackRAII Forget(getDerived());
-
+ Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(getSema(), -1);
ExprResult Out = getDerived().TransformExpr(Pattern);
if (Out.isInvalid())
return true;
>From 97fbf34c3edd09348fb48b4dc66f1d854516e8ef Mon Sep 17 00:00:00 2001
From: Utkarsh Saxena <[email protected]>
Date: Wed, 11 Sep 2024 11:59:58 +0000
Subject: [PATCH 2/2] Add comment
---
clang/lib/Sema/TreeTransform.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index a40673b04764da..0de43d2127b12f 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -4361,6 +4361,7 @@ bool TreeTransform<Derived>::TransformExprs(Expr *const
*Inputs,
// forgetting the partially-substituted parameter pack.
if (RetainExpansion) {
ForgetPartiallySubstitutedPackRAII Forget(getDerived());
+ // Simple transform producing another pack expansion.
Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(getSema(), -1);
ExprResult Out = getDerived().TransformExpr(Pattern);
if (Out.isInvalid())
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