Make globals used for array initialization codegen constant

As pointed out in D133835 these globals will never be written to
(they're only used for trivially copyable types), so they can always be
constant.

Differential revision: https://reviews.llvm.org/D146211

Author: zmodem

clang/lib/CodeGen/CGExprAgg.cpp

@@ -532,9 +532,8 @@ void AggExprEmitter::EmitArrayInit(Address DestPtr, llvm::ArrayType *AType,
             Emitter.tryEmitForInitializer(ExprToVisit, AS, ArrayQTy)) {
       auto GV = new llvm::GlobalVariable(
           CGM.getModule(), C->getType(),
-          CGM.isTypeConstant(ArrayQTy, /* ExcludeCtor= */ true,
-                             /* ExcludeDtor= */ false),
-          llvm::GlobalValue::PrivateLinkage, C, "constinit",
+          /* isConstant= */ true, llvm::GlobalValue::PrivateLinkage, C,
+          "constinit",
           /* InsertBefore= */ nullptr, llvm::GlobalVariable::NotThreadLocal,
           CGM.getContext().getTargetAddressSpace(AS));
       Emitter.finalize(GV);

clang/test/CodeGen/init.c

@@ -10,7 +10,7 @@ unsigned v2[2][3] = {[0 ... 1][0 ... 1] = 2222, 3333};
 
 // CHECK-DAG: [1 x %struct.M] [%struct.M { [2 x %struct.I] [%struct.I { [3 x i32] [i32 4, i32 4, i32 0] }, %struct.I { [3 x i32] [i32 4, i32 4, i32 5] }] }],
 // CHECK-DAG: [2 x [3 x i32]] {{[[][[]}}3 x i32] [i32 2222, i32 2222, i32 0], [3 x i32] [i32 2222, i32 2222, i32 3333]],
-// CHECK-DAG: [[INIT14:.*]] = private global [16 x i32] [i32 0, i32 0, i32 0, i32 0, i32 0, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 0, i32 0, i32 0, i32 0], align 4
+// CHECK-DAG: [[INIT14:.*]] = private constant [16 x i32] [i32 0, i32 0, i32 0, i32 0, i32 0, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 17, i32 0, i32 0, i32 0, i32 0], align 4
 
 void f1(void) {
   // Scalars in braces.

clang/test/CodeGen/label-array-aggregate-init.c

@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm %s -o - | FileCheck %s
 
-// CHECK: @constinit = private global [3 x ptr] [ptr blockaddress(@main, %L), ptr null, ptr null]
+// CHECK: @constinit = private constant [3 x ptr] [ptr blockaddress(@main, %L), ptr null, ptr null]
 
 void receivePtrs(void **);