Fix MaterializeTemporaryExpr's type when its an incomplete array.

[erichkeane]

Summary

Like the VarDecl that gets its type updated based on an init-list, this
patch corrects the MaterializeTemporaryExpr's type to make sure it isn't
creating an incomplete type, which leads to a handful of CodeGen crashes
(see PR 47636).

Based on @rsmith 's comments on D88236

[erichkeane]

clang/lib/Sema/SemaInit.cpp

8203

It seemed less intrusive/more reliable to fix this during the init-process, and perhaps would fix a few additional cases. The VarDecl gets updated by the caller of this, and updating both the ExprWtihCleanups and MTE seemed error-prone.

[erichkeane]

*PING!* Any feedback?

[erichkeane]

Ping! This was requested in post-commit on the last patch, so I'm hoping it shouldn't be too controversial.

[erichkeane]

Ping!

[rjmccall]

LGTM

clang/lib/Sema/SemaInit.cpp

for (step_iterator Step = step_begin(), StepEnd = step_end();
     case SK_BindReferenceToTemporary: {
       // Make sure the "temporary" is actually an rvalue.
       assert(CurInit.get()->isRValue() && "not a temporary");
 
       // Check exception specifications
       if (S.CheckExceptionSpecCompatibility(CurInit.get(), DestType))
         return ExprError();
 
+      QualType MTETy = Step->Type;
+
+      // When this is an incomplete array type (such as when this is
+      // initializing an array of unknown bounds from an init list), use THAT
+      // type instead so that we propogate the array bounds.
+      if (MTETy->isIncompleteArrayType() &&
+          !CurInit.get()->getType()->isIncompleteArrayType() &&
+          S.Context.hasSameType(
+              MTETy->getPointeeOrArrayElementType(),
+              CurInit.get()->getType()->getPointeeOrArrayElementType()))
+        MTETy = CurInit.get()->getType();
+
       // Materialize the temporary into memory.
       MaterializeTemporaryExpr *MTE = S.CreateMaterializeTemporaryExpr(
-          Step->Type, CurInit.get(), Entity.getType()->isLValueReferenceType());
+          MTETy, CurInit.get(), Entity.getType()->isLValueReferenceType());
       CurInit = MTE;
 
       // If we're extending this temporary to automatic storage duration -- we
       // need to register its cleanup during the full-expression's cleanups.
       if (MTE->getStorageDuration() == SD_Automatic &&
           MTE->getType().isDestructedType())
         S.Cleanup.setExprNeedsCleanups(true);
       break;

clang/test/AST/pr47636.cpp

+// RUN: %clang_cc1 -fsyntax-only %s -ast-dump | FileCheck %s
+
+int(&&intu_rvref)[] {1,2,3,4};
+// CHECK: VarDecl 0x[[GLOB_ADDR:[0-9a-f]+]] {{.*}} intu_rvref 'int (&&)[4]' listinit
+// CHECK-NEXT: ExprWithCleanups {{.*}} 'int [4]' xvalue
+// CHECK-NEXT: MaterializeTemporaryExpr {{.*}} 'int [4]' xvalue extended by Var 0x[[GLOB_ADDR]] 'intu_rvref' 'int (&&)[4]'
+// CHECK-NEXT: InitListExpr {{.*}} 'int [4]'
+
+// CHECK: FunctionDecl {{.*}} static_const
+void static_const() {
+  static const int(&&intu_rvref)[] {1,2,3,4};
+  // CHECK: VarDecl 0x[[STATIC_ADDR:[0-9a-f]+]] {{.*}} intu_rvref 'const int (&&)[4]' static listinit
+  // CHECK-NEXT: ExprWithCleanups {{.*}} 'const int [4]' xvalue
+  // CHECK-NEXT: MaterializeTemporaryExpr {{.*}} 'const int [4]' xvalue extended by Var 0x[[STATIC_ADDR]] 'intu_rvref' 'const int (&&)[4]'
+  // CHECK-NEXT: InitListExpr {{.*}} 'const int [4]'
+}
+
+// CHECK: FunctionDecl {{.*}} const_expr
+constexpr int const_expr() {
+  int(&&intu_rvref)[]{1, 2, 3, 4};
+  // CHECK: VarDecl 0x[[CE_ADDR:[0-9a-f]+]] {{.*}} intu_rvref 'int (&&)[4]' listinit
+  // CHECK-NEXT: ExprWithCleanups {{.*}} 'int [4]' xvalue
+  // CHECK-NEXT: MaterializeTemporaryExpr {{.*}} 'int [4]' xvalue extended by Var 0x[[CE_ADDR]] 'intu_rvref' 'int (&&)[4]'
+  // CHECK-NEXT: InitListExpr {{.*}} 'int [4]'
+  return intu_rvref[0];
+}

clang/test/CodeGenCXX/pr47636.cpp

 // RUN: %clang_cc1 -o - -emit-llvm -triple x86_64-linux-pc %s | FileCheck %s
 int(&&intu_rvref)[] {1,2,3,4};
 // CHECK: @_ZGR10intu_rvref_ = internal global [4 x i32] [i32 1, i32 2, i32 3, i32 4]
 // CHECK: @intu_rvref ={{.*}} constant [4 x i32]* @_ZGR10intu_rvref_
 
 void foo() {
   static const int(&&intu_rvref)[] {1,2,3,4};
   // CHECK: @_ZZ3foovE10intu_rvref = internal constant [4 x i32]* @_ZGRZ3foovE10intu_rvref_
   // CHECK: @_ZGRZ3foovE10intu_rvref_ = internal constant [4 x i32] [i32 1, i32 2, i32 3, i32 4]
 }
+
+// Example given on review, ensure this doesn't crash as well.
+constexpr int f() {
+  // CHECK: i32 @_Z1fv()
+  int(&&intu_rvref)[]{1, 2, 3, 4};
+  // CHECK: %{{.*}} = alloca [4 x i32]*
+  return intu_rvref[2];
+}
+
+void use_f() {
+  int i = f();
+}