[Clang] Fix instantiation of OpaqueValueExprs (Bug #45964)

The structured bindings decomposition of a non-dependent array in a dependent context (a template) were, upon instantiation, creating nested OpaqueValueExprs that would trigger assertions in CodeGen. Additionally the OpaqueValuesExpr's contained SourceExpr is being emitted in CodeGen, but there was no code for its transform in template instantiation. This would trigger other assertions such as when emitting a DeclRefExpr that refers to a VarDecl that is not marked as ODR-used.

This is all based on cursory deduction, but with the way the code flows from SemaTemplateInstantiate back to SemaInit, it is apparent that the nesting of OpaqueValueExpr is unintentional.

This commit fixes https://bugs.llvm.org/show_bug.cgi?id=45964 and possible other issues involving OpaqueValueExprs in template instantiations might be resolved.

Reviewed By: aaron.ballman, rjmccall

Differential Revision: https://reviews.llvm.org/D108482

clang/lib/Sema/TreeTransform.h

@@ -3853,8 +3853,10 @@ ExprResult TreeTransform<Derived>::TransformInitializer(Expr *Init,
   if (auto *FE = dyn_cast<FullExpr>(Init))
     Init = FE->getSubExpr();
 
-  if (auto *AIL = dyn_cast<ArrayInitLoopExpr>(Init))
-    Init = AIL->getCommonExpr();
+  if (auto *AIL = dyn_cast<ArrayInitLoopExpr>(Init)) {
+    OpaqueValueExpr *OVE = AIL->getCommonExpr();
+    Init = OVE->getSourceExpr();
+  }
 
   if (MaterializeTemporaryExpr *MTE = dyn_cast<MaterializeTemporaryExpr>(Init))
     Init = MTE->getSubExpr();

clang/test/CodeGenCXX/pr45964-decomp-transform.cpp

@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+
+int a[1];
+// CHECK: @a = global [1 x i32] zeroinitializer
+template <int>
+void test_transform() {
+  auto [b] = a;
+}
+void (*d)(){test_transform<0>};
+// CHECK-LABEL: define {{.*}} @_Z14test_transformILi0EEvv
+// CHECK:       [[ENTRY:.*]]:
+// CHECK-NEXT:  [[ARR:%.*]] = alloca [1 x i32]
+// CHECK-NEXT:  [[BEGIN:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* [[ARR]], i64 0, i64 0
+// CHECK-NEXT:  br label %[[BODY:.*]]
+// CHECK-EMPTY:
+// CHECK-NEXT:  [[BODY]]:
+// CHECK-NEXT:  [[CUR:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[NEXT:%.*]], %[[BODY]] ]
+// CHECK-NEXT:  [[DEST:%.*]] = getelementptr inbounds i32, i32* [[BEGIN]], i64 [[CUR]]
+// CHECK-NEXT:  [[SRC:%.*]] = getelementptr inbounds [1 x i32], [1 x i32]* @a, i64 0, i64 [[CUR]]
+// CHECK-NEXT:  [[X:%.*]] = load i32, i32* [[SRC]]
+// CHECK-NEXT:  store i32 [[X]], i32* [[DEST]]
+// CHECK-NEXT:  [[NEXT]] = add nuw i64 [[CUR]], 1
+// CHECK-NEXT:  [[EQ:%.*]] = icmp eq i64 [[NEXT]], 1
+// CHECK-NEXT:  br i1 [[EQ]], label %[[FIN:.*]], label %[[BODY]]
+// CHECK-EMPTY:
+// CHECK-NEXT:  [[FIN]]:
+// CHECK-NEXT:  ret void