r374119 - Fix crash or wrong code bug if a lifetime-extended temporary contains a

[Richard Smith via cfe-commits]

Author: rsmith
Date: Tue Oct  8 14:26:03 2019
New Revision: 374119

URL: http://llvm.org/viewvc/llvm-project?rev=374119&view=rev
Log:
Fix crash or wrong code bug if a lifetime-extended temporary contains a
"non-constant" value.

If the constant evaluator evaluates part of a variable initializer,
including the initializer for some lifetime-extended temporary, but
fails to fully evaluate the initializer, it can leave behind wrong
values for temporaries encountered in that initialization. Don't try to
emit those from CodeGen! Instead, look at the values that constant
evaluation produced if (and only if) it actually succeeds and we're
emitting the lifetime-extending declaration's initializer as a constant.

Added:
    cfe/trunk/test/CodeGenCXX/no-const-init-cxx2a.cpp
Modified:
    cfe/trunk/lib/AST/ExprConstant.cpp
    cfe/trunk/lib/CodeGen/CodeGenModule.cpp

Modified: cfe/trunk/lib/AST/ExprConstant.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=374119&r1=374118&r2=374119&view=diff
==============================================================================
--- cfe/trunk/lib/AST/ExprConstant.cpp (original)
+++ cfe/trunk/lib/AST/ExprConstant.cpp Tue Oct  8 14:26:03 2019
@@ -13569,8 +13569,10 @@ bool Expr::EvaluateAsConstantExpr(EvalRe
   if (!Info.discardCleanups())
     llvm_unreachable("Unhandled cleanup; missing full expression marker?");
 
-  return CheckConstantExpression(Info, getExprLoc(), getType(), Result.Val,
-                                 Usage) &&
+  QualType T = getType();
+  if (!isRValue())
+    T = Ctx.getLValueReferenceType(T);
+  return CheckConstantExpression(Info, getExprLoc(), T, Result.Val, Usage) &&
          CheckMemoryLeaks(Info);
 }
 

Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=374119&r1=374118&r2=374119&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Tue Oct  8 14:26:03 2019
@@ -4978,14 +4978,13 @@ ConstantAddress CodeGenModule::GetAddrOf
       VD, E->getManglingNumber(), Out);
 
   APValue *Value = nullptr;
-  if (E->getStorageDuration() == SD_Static) {
-    // We might have a cached constant initializer for this temporary. Note
-    // that this might have a different value from the value computed by
-    // evaluating the initializer if the surrounding constant expression
-    // modifies the temporary.
+  if (E->getStorageDuration() == SD_Static && VD && VD->evaluateValue()) {
+    // If the initializer of the extending declaration is a constant
+    // initializer, we should have a cached constant initializer for this
+    // temporary. Note that this might have a different value from the value
+    // computed by evaluating the initializer if the surrounding constant
+    // expression modifies the temporary.
     Value = getContext().getMaterializedTemporaryValue(E, false);
-    if (Value && Value->isAbsent())
-      Value = nullptr;
   }
 
   // Try evaluating it now, it might have a constant initializer.

Added: cfe/trunk/test/CodeGenCXX/no-const-init-cxx2a.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/no-const-init-cxx2a.cpp?rev=374119&view=auto
==============================================================================
--- cfe/trunk/test/CodeGenCXX/no-const-init-cxx2a.cpp (added)
+++ cfe/trunk/test/CodeGenCXX/no-const-init-cxx2a.cpp Tue Oct  8 14:26:03 2019
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s -std=c++2a | FileCheck %s
+
+// CHECK-DAG: @p = {{.*}} null
+// CHECK-DAG: @_ZGR1p_ = {{.*}} null
+int *const &p = new int;
+
+struct d {
+  constexpr d(int &&f) : e(f) {}
+  int &e;
+};
+
+// CHECK-DAG: @g = {{.*}} null
+// CHECK-DAG: @_ZGR1g_ = {{.*}} zeroinitializer
+d &&g{{0}};
+
+// CHECK: define {{.*}} @__cxx_global_var_init
+// CHECK: define {{.*}} @__cxx_global_var_init
+// CHECK-NOT: define {{.*}} @__cxx_global_var_init