Merging r371548:

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r371548 | abataev | 2019-09-10 12:16:56 -0700 (Tue, 10 Sep 2019) | 10 lines

Fix for PR43175: compiler crash when trying to emit noncapturable
constant.

If the constexpr variable is partially initialized, the initializer can
be emitted as the structure, not as an array, because of some early
optimizations. The llvm variable gets the type from this constant and,
thus, gets the type which is pointer to struct rather than pointer to an
array. We need to convert this type to be truely array, otherwise it may
lead to the compiler crash when trying to emit array subscript
expression.
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clang/lib/CodeGen/CGExpr.cpp

@@ -2540,6 +2540,11 @@ LValue CodeGenFunction::EmitDeclRefLValue(const DeclRefExpr *E) {
         // Spill the constant value to a global.
         Addr = CGM.createUnnamedGlobalFrom(*VD, Val,
                                            getContext().getDeclAlign(VD));
+        llvm::Type *VarTy = getTypes().ConvertTypeForMem(VD->getType());
+        auto *PTy = llvm::PointerType::get(
+            VarTy, getContext().getTargetAddressSpace(VD->getType()));
+        if (PTy != Addr.getType())
+          Addr = Builder.CreatePointerBitCastOrAddrSpaceCast(Addr, PTy);
       } else {
         // Should we be using the alignment of the constant pointer we emitted?
         CharUnits Alignment =

clang/test/OpenMP/constexpr_partial_array.cpp

@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -verify -triple x86_64-pc-windows-msvc19.22.27905 -emit-llvm -o - -fopenmp %s | FileCheck %s
+// expected-no-diagnostics
+
+// CHECK: [[C_VAR_VAL:@.+]] = private unnamed_addr constant <{ i8, [26 x i8] }> <{ i8 1, [26 x i8] zeroinitializer }>,
+char a;
+bool b() {
+  static constexpr bool c[27]{1};
+  // CHECK: getelementptr inbounds [27 x i8], [27 x i8]* bitcast (<{ i8, [26 x i8] }>* [[C_VAR_VAL]] to [27 x i8]*),
+  return c[a];
+}