[PATCH] D10938: [Sema] Warn when shifting a negative value

[Richard Smith]

rsmith accepted this revision.

This revision is now accepted and ready to land.

LGTM


================
Comment at: lib/Sema/SemaExpr.cpp:7940-7941
@@ -7939,4 +7939,4 @@
   if (LHS.get()->isValueDependent() ||
-      !LHS.get()->isIntegerConstantExpr(Left, S.Context) ||
+      !LHS.get()->EvaluateAsInt(Left, S.Context) ||
       LHSType->hasUnsignedIntegerRepresentation())
     return;
----------------
While you're here, please reverse the order of these two lines. It's much cheaper to check for an unsigned type than to evaluate the expression.

================
Comment at: test/Sema/shift.c:42
@@ -41,3 +41,3 @@
   i = 1 << (WORD_BIT - 1); // expected-warning {{sets the sign bit of the shift expression}}
-  i = -1 << (WORD_BIT - 1);
+  i = -1 << (WORD_BIT - 1); // expected-warning {{shifting a negative signed value is undefined}}
   i = 0 << (WORD_BIT - 1);
----------------
Please also add a test that we even warn for shifting a negative value by zero.


Repository:
  rL LLVM

http://reviews.llvm.org/D10938