From 6cc8317c38b8fd9b4debeabf5d28aa128bb61160 Mon Sep 17 00:00:00 2001
From: Alex Lorenz <arphaman@gmail.com>
Date: Fri, 25 Aug 2017 10:07:00 +0000
Subject: [IRGen] Evaluate constant static variables referenced through member
 expressions

C++ allows us to reference static variables through member expressions. Prior to
this commit, non-integer static variables that were referenced using a member
expression were always emitted using lvalue loads. The old behaviour introduced
an inconsistency between regular uses of static variables and member expressions
uses. For example, the following program compiled and linked successfully:

struct Foo {
   constexpr static const char *name = "foo";
};
int main() {
  return Foo::name[0] == 'f';
}

but this program failed to link because "Foo::name" wasn't found:

struct Foo {
   constexpr static const char *name = "foo";
};
int main() {
  Foo f;
  return f.name[0] == 'f';
}

This commit ensures that constant static variables referenced through member
expressions are emitted in the same way as ordinary static variable references.

rdar://33942261

Differential Revision: https://reviews.llvm.org/D36876

llvm-svn: 311772
---
 clang/lib/CodeGen/CGExprComplex.cpp | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

(limited to 'clang/lib/CodeGen/CGExprComplex.cpp')

diff --git a/clang/lib/CodeGen/CGExprComplex.cpp b/clang/lib/CodeGen/CGExprComplex.cpp
index 980972370dc..f019e3586e3 100644
--- a/clang/lib/CodeGen/CGExprComplex.cpp
+++ b/clang/lib/CodeGen/CGExprComplex.cpp
@@ -120,18 +120,22 @@ public:
     return Visit(E->getSubExpr());
   }
 
+  ComplexPairTy emitConstant(const CodeGenFunction::ConstantEmission &Constant,
+                             Expr *E) {
+    assert(Constant && "not a constant");
+    if (Constant.isReference())
+      return EmitLoadOfLValue(Constant.getReferenceLValue(CGF, E),
+                              E->getExprLoc());
+
+    llvm::Constant *pair = Constant.getValue();
+    return ComplexPairTy(pair->getAggregateElement(0U),
+                         pair->getAggregateElement(1U));
+  }
 
   // l-values.
   ComplexPairTy VisitDeclRefExpr(DeclRefExpr *E) {
-    if (CodeGenFunction::ConstantEmission result = CGF.tryEmitAsConstant(E)) {
-      if (result.isReference())
-        return EmitLoadOfLValue(result.getReferenceLValue(CGF, E),
-                                E->getExprLoc());
-
-      llvm::Constant *pair = result.getValue();
-      return ComplexPairTy(pair->getAggregateElement(0U),
-                           pair->getAggregateElement(1U));
-    }
+    if (CodeGenFunction::ConstantEmission Constant = CGF.tryEmitAsConstant(E))
+      return emitConstant(Constant, E);
     return EmitLoadOfLValue(E);
   }
   ComplexPairTy VisitObjCIvarRefExpr(ObjCIvarRefExpr *E) {
@@ -141,7 +145,14 @@ public:
     return CGF.EmitObjCMessageExpr(E).getComplexVal();
   }
   ComplexPairTy VisitArraySubscriptExpr(Expr *E) { return EmitLoadOfLValue(E); }
-  ComplexPairTy VisitMemberExpr(const Expr *E) { return EmitLoadOfLValue(E); }
+  ComplexPairTy VisitMemberExpr(MemberExpr *ME) {
+    if (CodeGenFunction::ConstantEmission Constant =
+            CGF.tryEmitAsConstant(ME)) {
+      CGF.EmitIgnoredExpr(ME->getBase());
+      return emitConstant(Constant, ME);
+    }
+    return EmitLoadOfLValue(ME);
+  }
   ComplexPairTy VisitOpaqueValueExpr(OpaqueValueExpr *E) {
     if (E->isGLValue())
       return EmitLoadOfLValue(CGF.getOpaqueLValueMapping(E), E->getExprLoc());
-- 
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