[clang] [CGExprConstant] stop calling into ConstExprEmitter for Reference type destinations (PR #70366)

[Nick Desaulniers via cfe-commits]

https://github.com/nickdesaulniers updated https://github.com/llvm/llvm-project/pull/70366

>From 52e5c1083f82c045dc0af26badf159e8b1593bd1 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Thu, 26 Oct 2023 11:11:29 -0700
Subject: [PATCH 1/3] [CGExprConstant] stop evaluating StringLiterals for
 non-ConstantArrayTypes

Fixes a bug introduced by
commit b54294e2c959 ("[clang][ConstantEmitter] have tryEmitPrivate[ForVarInit] try ConstExprEmitter fast-path first")

In the added test case, the QualType is a LValueReferenceType.
  LValueReferenceType 0x558412998d90 'const char (&)[41]'
  `-ParenType 0x558412998d30 'const char[41]' sugar
    `-ConstantArrayType 0x558412998cf0 'const char[41]' 41
      `-QualType 0x55841294c271 'const char' const
        `-BuiltinType 0x55841294c270 'char'
---
 clang/lib/CodeGen/CGExprConstant.cpp       | 3 +++
 clang/test/CodeGenCXX/const-init-cxx11.cpp | 6 ++++++
 2 files changed, 9 insertions(+)

diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 9b67a8b3335a165..0706647bf45466d 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -22,6 +22,7 @@
 #include "clang/AST/Attr.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtVisitor.h"
+#include "clang/AST/Type.h"
 #include "clang/Basic/Builtins.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Sequence.h"
@@ -1358,6 +1359,8 @@ class ConstExprEmitter :
   }
 
   llvm::Constant *VisitStringLiteral(StringLiteral *E, QualType T) {
+    if (!isa<ConstantArrayType>(T.getDesugaredType(CGM.getContext())))
+      return nullptr;
     // This is a string literal initializing an array in an initializer.
     return CGM.GetConstantArrayFromStringLiteral(E);
   }
diff --git a/clang/test/CodeGenCXX/const-init-cxx11.cpp b/clang/test/CodeGenCXX/const-init-cxx11.cpp
index d22d78d2b94edb5..3a12fe444f137bf 100644
--- a/clang/test/CodeGenCXX/const-init-cxx11.cpp
+++ b/clang/test/CodeGenCXX/const-init-cxx11.cpp
@@ -424,6 +424,8 @@ namespace DR2126 {
 // CHECK: @_ZN33ClassTemplateWithStaticDataMember3useE ={{.*}} constant ptr @_ZGRN33ClassTemplateWithStaticDataMember1SIvE1aE_
 // CHECK: @_ZGRN39ClassTemplateWithHiddenStaticDataMember1SIvE1aE_ = linkonce_odr hidden constant i32 5, comdat
 // CHECK: @_ZN39ClassTemplateWithHiddenStaticDataMember3useE ={{.*}} constant ptr @_ZGRN39ClassTemplateWithHiddenStaticDataMember1SIvE1aE_
+// CHECK: @.str.[[STR:[0-9]+]] ={{.*}} constant [9 x i8] c"12345678\00"
+// CHECK-NEXT: @e = global %struct.PR69979 { ptr @.str.[[STR]] }
 // CHECK: @_ZGRZN20InlineStaticConstRef3funEvE1i_ = linkonce_odr constant i32 10, comdat
 // CHECK20: @_ZZN12LocalVarInit4dtorEvE1a = internal constant {{.*}} i32 103
 
@@ -632,6 +634,10 @@ struct X {
 const char *f() { return &X::p; }
 }
 
+struct PR69979 {
+  const char (&d)[9];
+} e {"12345678"};
+
 // VirtualMembers::TemplateClass::templateMethod() must be defined in this TU,
 // not just declared.
 // CHECK: define linkonce_odr void @_ZN14VirtualMembers13TemplateClassIiE14templateMethodEv(ptr {{[^,]*}} %this)

>From 4cff8f0f1cb4bba84f32d3953a5abfafd13c6b09 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Fri, 27 Oct 2023 13:47:28 -0700
Subject: [PATCH 2/3] skip calling into ConstExprEmitter for reference type
 destinations instead

---
 clang/lib/CodeGen/CGExprConstant.cpp | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 0706647bf45466d..7eb28ae4c4ff173 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -1359,8 +1359,6 @@ class ConstExprEmitter :
   }
 
   llvm::Constant *VisitStringLiteral(StringLiteral *E, QualType T) {
-    if (!isa<ConstantArrayType>(T.getDesugaredType(CGM.getContext())))
-      return nullptr;
     // This is a string literal initializing an array in an initializer.
     return CGM.GetConstantArrayFromStringLiteral(E);
   }
@@ -1778,9 +1776,10 @@ llvm::Constant *ConstantEmitter::tryEmitPrivate(const Expr *E,
                                                 QualType destType) {
   assert(!destType->isVoidType() && "can't emit a void constant");
 
-  if (llvm::Constant *C =
-          ConstExprEmitter(*this).Visit(const_cast<Expr *>(E), destType))
-    return C;
+  if (!destType->isReferenceType())
+    if (llvm::Constant *C =
+            ConstExprEmitter(*this).Visit(const_cast<Expr *>(E), destType))
+      return C;
 
   Expr::EvalResult Result;
 

>From 9a33ea9b7655b510d489eede1359801e0107ff50 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Fri, 27 Oct 2023 13:49:46 -0700
Subject: [PATCH 3/3] remove unnecessary header

---
 clang/lib/CodeGen/CGExprConstant.cpp | 1 -
 1 file changed, 1 deletion(-)

diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 7eb28ae4c4ff173..3f508032e30d658 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -22,7 +22,6 @@
 #include "clang/AST/Attr.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtVisitor.h"
-#include "clang/AST/Type.h"
 #include "clang/Basic/Builtins.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Sequence.h"