If the first argument of __builtin_object_size can be folded to a constant

pointer, but such folding encounters side-effects, ignore the side-effects
rather than performing them at runtime: CodeGen generates wrong code for
__builtin_object_size in that case.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157310 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 4 deletions

diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 5362320f49..d3ab84fc4a 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -4319,10 +4319,16 @@ QualType IntExprEvaluator::GetObjectType(APValue::LValueBase B) {
 }
 
 bool IntExprEvaluator::TryEvaluateBuiltinObjectSize(const CallExpr *E) {
-  // TODO: Perhaps we should let LLVM lower this?
   LValue Base;
-  if (!EvaluatePointer(E->getArg(0), Base, Info))
-    return false;
+
+  {
+    // The operand of __builtin_object_size is never evaluated for side-effects.
+    // If there are any, but we can determine the pointed-to object anyway, then
+    // ignore the side-effects.
+    SpeculativeEvaluationRAII SpeculativeEval(Info);
+    if (!EvaluatePointer(E->getArg(0), Base, Info))
+      return false;
+  }
 
   // If we can prove the base is null, lower to zero now.
   if (!Base.getLValueBase()) return Success(0, E);
@@ -4355,13 +4361,16 @@ bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
       return true;
 
     // If evaluating the argument has side-effects we can't determine
-    // the size of the object and lower it to unknown now.
+    // the size of the object and lower it to unknown now. CodeGen relies on
+    // us to handle all cases where the expression has side-effects.
     if (E->getArg(0)->HasSideEffects(Info.Ctx)) {
       if (E->getArg(1)->EvaluateKnownConstInt(Info.Ctx).getZExtValue() <= 1)
         return Success(-1ULL, E);
       return Success(0, E);
     }
 
+    // Expression had no side effects, but we couldn't statically determine the
+    // size of the referenced object.
     return Error(E);
   }