Teach the aggressive constant folder to fold X && 0 -> 0 and X || 1 -> 1
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59105 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 99fa8d5..e2be9f1 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -323,8 +323,28 @@
bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
// The LHS of a constant expr is always evaluated and needed.
llvm::APSInt RHS(32);
- if (!Visit(E->getLHS()))
+ if (!Visit(E->getLHS())) {
+ // If the LHS is unfoldable, we generally can't fold this. However, if this
+ // is a logical operator like &&/||, and if we know that the RHS determines
+ // the outcome of the result (e.g. X && 0), return the outcome.
+ if (!E->isLogicalOp())
+ return false;
+
+ // If this is a logical op, see if the RHS determines the outcome.
+ EvalInfo Info2(Info.Ctx);
+ if (!EvaluateInteger(E->getRHS(), RHS, Info2))
+ return false;
+
+ // X && 0 -> 0, X || 1 -> 1.
+ if (E->getOpcode() == BinaryOperator::LAnd && RHS == 0 ||
+ E->getOpcode() == BinaryOperator::LOr && RHS != 0) {
+ Result = RHS != 0;
+ Result.zextOrTrunc(getIntTypeSizeInBits(E->getType()));
+ return true;
+ }
+
return false; // error in subexpression.
+ }
bool OldEval = Info.isEvaluated;