Scalar shifts in the OpenCL specification (as of v. 1.2) are defined to be

with respect to the lower "left-hand-side bitwidth" bits, even when negative);
see OpenCL spec 6.3j. This patch both implements this behaviour in the code
generator and "constant folding" bits of Sema, and also prevents tests
to detect undefinedness in terms of the weaker C99 or C++ specifications
from being applied. 


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171755 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 6 deletions

diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index a472951ab6..338cd74b32 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -4708,9 +4708,14 @@ bool DataRecursiveIntBinOpEvaluator::
       return Success(E->getOpcode() == BO_Rem ? LHS % RHS : LHS / RHS, E,
                      Result);
     case BO_Shl: {
-      // During constant-folding, a negative shift is an opposite shift. Such
-      // a shift is not a constant expression.
-      if (RHS.isSigned() && RHS.isNegative()) {
+      if (Info.getLangOpts().OpenCL)
+        // OpenCL 6.3j: shift values are effectively % word size of LHS.
+        RHS &= APSInt(llvm::APInt(LHS.getBitWidth(),
+                      static_cast<uint64_t>(LHS.getBitWidth() - 1)),
+                      RHS.isUnsigned());
+      else if (RHS.isSigned() && RHS.isNegative()) {
+        // During constant-folding, a negative shift is an opposite shift. Such
+        // a shift is not a constant expression.
         CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
         RHS = -RHS;
         goto shift_right;
@@ -4735,9 +4740,14 @@ bool DataRecursiveIntBinOpEvaluator::
       return Success(LHS << SA, E, Result);
     }
     case BO_Shr: {
-      // During constant-folding, a negative shift is an opposite shift. Such a
-      // shift is not a constant expression.
-      if (RHS.isSigned() && RHS.isNegative()) {
+      if (Info.getLangOpts().OpenCL)
+        // OpenCL 6.3j: shift values are effectively % word size of LHS.
+        RHS &= APSInt(llvm::APInt(LHS.getBitWidth(),
+                      static_cast<uint64_t>(LHS.getBitWidth() - 1)),
+                      RHS.isUnsigned());
+      else if (RHS.isSigned() && RHS.isNegative()) {
+        // During constant-folding, a negative shift is an opposite shift. Such a
+        // shift is not a constant expression.
         CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
         RHS = -RHS;
         goto shift_left;