Fix crash with align_value diagnostic reporting

[AaronBallman]

We were passing the address of a local variable to a call to Diag() which then tried to use the object after its lifetime ended, resulting in crashes. We no longer pass the temporary object any longer.

Fixes #26612

[AaronBallman]

Note, I filed an issue about the duplicate diagnostics at #135012

[llvmbot]

@llvm/pr-subscribers-clang

Author: Aaron Ballman (AaronBallman)

Changes

We were passing the address of a local variable to a call to Diag() which then tried to use the object after its lifetime ended, resulting in crashes. We no longer pass the temporary object any longer.

Fixes #26612

---

Full diff: https://github.com/llvm/llvm-project/pull/135013.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+4)
• (modified) clang/lib/Sema/SemaDeclAttr.cpp (+1-2)
• (modified) clang/test/SemaCXX/align_value.cpp (+14)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5b702b56038f7..cd16641c25ed8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -386,6 +386,10 @@ Bug Fixes to Attribute Support
   or too few attribute argument indicies for the specified callback function.
   (#GH47451)
 
+- No longer crashing on ``__attribute__((align_value(N)))`` during template
+  instantiation when the function parameter type is not a pointer or reference.
+  (#GH26612)
+
 Bug Fixes to C++ Support
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index d76afe9d6464d..b3c0367ed51b2 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4383,7 +4383,6 @@ static void handleAlignValueAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
 }
 
 void Sema::AddAlignValueAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E) {
-  AlignValueAttr TmpAttr(Context, CI, E);
   SourceLocation AttrLoc = CI.getLoc();
 
   QualType T;
@@ -4397,7 +4396,7 @@ void Sema::AddAlignValueAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E) {
   if (!T->isDependentType() && !T->isAnyPointerType() &&
       !T->isReferenceType() && !T->isMemberPointerType()) {
     Diag(AttrLoc, diag::warn_attribute_pointer_or_reference_only)
-      << &TmpAttr << T << D->getSourceRange();
+      << CI << T << D->getSourceRange();
     return;
   }
 
diff --git a/clang/test/SemaCXX/align_value.cpp b/clang/test/SemaCXX/align_value.cpp
index 519868201f994..ad89791902e7f 100644
--- a/clang/test/SemaCXX/align_value.cpp
+++ b/clang/test/SemaCXX/align_value.cpp
@@ -24,3 +24,17 @@ struct nope {
 // expected-note@+1 {{in instantiation of template class 'nope<long double, 4>' requested here}}
 nope<long double, 4> y2;
 
+namespace GH26612 {
+// This used to crash while issuing the diagnostic about only applying to a
+// pointer or reference type.
+// FIXME: it would be ideal to only diagnose once rather than twice. We get one
+// diagnostic from explicit template arguments and another one for deduced
+// template arguments, which seems silly.
+template <class T>
+void f(T __attribute__((align_value(4))) x) {} // expected-warning 2 {{'align_value' attribute only applies to a pointer or reference ('int' is invalid)}}
+
+void foo() {
+  f<int>(0); // expected-note {{while substituting explicitly-specified template arguments into function template 'f'}} \
+                expected-note {{while substituting deduced template arguments into function template 'f' [with T = int]}}
+}
+} // namespace GH26612

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