[clang] CTAD: build aggregate deduction guides for alias templates. (#85904)

Fixes https://github.com/llvm/llvm-project/issues/85767.

The aggregate deduction guides are handled in a separate code path. We
don't generate dedicated aggregate deduction guides for alias templates
(we just reuse the ones from the underlying template decl by accident).
The patch fixes this incorrect issue.

Note: there is a small refactoring change in this PR, where we move the
cache logic from `Sema::DeduceTemplateSpecializationFromInitializer` to
`Sema::DeclareImplicitDeductionGuideFromInitList`

1 files changed, 6 insertions, 22 deletions

diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index e2a1951..a75e992 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -10930,32 +10930,16 @@ QualType Sema::DeduceTemplateSpecializationFromInitializer(
                   Context.getLValueReferenceType(ElementTypes[I].withConst());
           }
 
-        llvm::FoldingSetNodeID ID;
-        ID.AddPointer(Template);
-        for (auto &T : ElementTypes)
-          T.getCanonicalType().Profile(ID);
-        unsigned Hash = ID.ComputeHash();
-        if (AggregateDeductionCandidates.count(Hash) == 0) {
-          if (FunctionTemplateDecl *TD =
-                  DeclareImplicitDeductionGuideFromInitList(
-                      Template, ElementTypes,
-                      TSInfo->getTypeLoc().getEndLoc())) {
-            auto *GD = cast<CXXDeductionGuideDecl>(TD->getTemplatedDecl());
-            GD->setDeductionCandidateKind(DeductionCandidate::Aggregate);
-            AggregateDeductionCandidates[Hash] = GD;
-            addDeductionCandidate(TD, GD, DeclAccessPair::make(TD, AS_public),
-                                  OnlyListConstructors,
-                                  /*AllowAggregateDeductionCandidate=*/true);
-          }
-        } else {
-          CXXDeductionGuideDecl *GD = AggregateDeductionCandidates[Hash];
-          FunctionTemplateDecl *TD = GD->getDescribedFunctionTemplate();
-          assert(TD && "aggregate deduction candidate is function template");
+        if (FunctionTemplateDecl *TD =
+                DeclareAggregateDeductionGuideFromInitList(
+                    LookupTemplateDecl, ElementTypes,
+                    TSInfo->getTypeLoc().getEndLoc())) {
+          auto *GD = cast<CXXDeductionGuideDecl>(TD->getTemplatedDecl());
           addDeductionCandidate(TD, GD, DeclAccessPair::make(TD, AS_public),
                                 OnlyListConstructors,
                                 /*AllowAggregateDeductionCandidate=*/true);
+          HasAnyDeductionGuide = true;
         }
-        HasAnyDeductionGuide = true;
       }
     };