fd503e5af3
This fixes a regression introduced by revision 268094. Revision 268094 added the following dag combine rule: // trunc (shl x, K) -> shl (trunc x), K => K < vt.size / 2 That rule converts a truncate of a shift-by-constant into a shift of a truncated value. We do this only if the shift count is less than half the size in bits of the truncated value (K < vt.size / 2). The problem is that the constraint on the shift count is incorrect, so the rule doesn't work well in some cases involving vector types. The combine rule should have been written instead like this: // trunc (shl x, K) -> shl (trunc x), K => K < vt.getScalarSizeInBits() Basically, if K is smaller than the "scalar size in bits" of the truncated value then we know that by "sinking" the truncate into the operand of the shift we would never accidentally make the shift undefined. This patch fixes the check on the shift count, and adds test cases to make sure that we don't regress the behavior. Differential Revision: https://reviews.llvm.org/D24154 llvm-svn: 280482
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