From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Tue, 31 Jan 2012 23:24:19 +0000 (+0000)
Subject: constexpr: Treat INT_MIN % -1 as undefined behavior in C++11. Technically, it
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3df61308ddfbdba0897b762a129b5a38750c87d0;p=clang

constexpr: Treat INT_MIN % -1 as undefined behavior in C++11. Technically, it
isn't, but this is just a (reported) defect in the wording.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149448 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index 5a385e6eb4..15ab15ce3d 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -4431,17 +4431,15 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
   case BO_Xor: return Success(LHS ^ RHS, E);
   case BO_Or:  return Success(LHS | RHS, E);
   case BO_Div:
+  case BO_Rem:
     if (RHS == 0)
       return Error(E, diag::note_expr_divide_by_zero);
-    // Check for overflow case: INT_MIN / -1.
+    // Check for overflow case: INT_MIN / -1 or INT_MIN % -1. The latter is not
+    // actually undefined behavior in C++11 due to a language defect.
     if (RHS.isNegative() && RHS.isAllOnesValue() &&
         LHS.isSigned() && LHS.isMinSignedValue())
       HandleOverflow(Info, E, -LHS.extend(LHS.getBitWidth() + 1), E->getType());
-    return Success(LHS / RHS, E);
-  case BO_Rem:
-    if (RHS == 0)
-      return Error(E, diag::note_expr_divide_by_zero);
-    return Success(LHS % RHS, E);
+    return Success(E->getOpcode() == BO_Rem ? LHS % RHS : LHS / RHS, E);
   case BO_Shl: {
     // During constant-folding, a negative shift is an opposite shift. Such a
     // shift is not a constant expression.
diff --git a/test/CXX/expr/expr.const/p2-0x.cpp b/test/CXX/expr/expr.const/p2-0x.cpp
index 617edc5faa..390364df63 100644
--- a/test/CXX/expr/expr.const/p2-0x.cpp
+++ b/test/CXX/expr/expr.const/p2-0x.cpp
@@ -134,6 +134,7 @@ namespace UndefinedBehavior {
   constexpr int div0 = 3 / 0; // expected-error {{constant expression}} expected-note {{division by zero}} expected-warning {{undefined}}
   constexpr int mod0 = 3 % 0; // expected-error {{constant expression}} expected-note {{division by zero}} expected-warning {{undefined}}
   constexpr int int_min_div_minus_1 = int_min / -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}}
+  constexpr int int_min_mod_minus_1 = int_min % -1; // expected-error {{constant expression}} expected-note {{value 2147483648 is outside the range}}
 
   constexpr int shl_m1 = 0 << -1; // expected-error {{constant expression}} expected-note {{negative shift count -1}} expected-warning {{negative}}
   constexpr int shl_0 = 0 << 0; // ok