[PATCH] D16460: Bug 10002 - [opencl] Wrongfully assuming RHS is always unsigned

[Igor Chesnokov via cfe-commits]

ichesnokov added inline comments.

================
Comment at: lib/CodeGen/CGExprScalar.cpp:2716
@@ +2715,3 @@
+  if (Ops.LHS->getType() != RHS->getType()) {
+    bool isSigned = dyn_cast<BinaryOperator>(Ops.E)->getRHS()->getType().getTypePtr()->isSignedIntegerType();
+    RHS = Builder.CreateIntCast(RHS, Ops.LHS->getType(), isSigned, "sh_prom");
----------------
The OpenCL 2.0 standard does not say anything about right operand sign of shift operators.

C standard says the behavior is undefined:
http://www.coding-guidelines.com/cbook/cbook1_0b.pdf, 1175
"If the value of the right operand is negative or is greater than or equal to the width of the promoted left
operand, the behavior is undefined."

In C++11 standard said the same:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4296.pdf, 5.8
"The behavior is undefined if the right operand
is negative, or greater than or equal to the length in bits of the promoted left operand"

I.e., we can close this bug as NAB and do not apply patch.
However, I believe that passing right operand, preserving it's sign, gives more flexibility to developers. It makes opportunity to developers use signed right operator, not only unsigned (if development is working for specific platform where developer knows what happens when right operand is signed).



Repository:
  rL LLVM

http://reviews.llvm.org/D16460