Merging r355116 and r355117:
r355116 | ctopper | 2019-02-28 19:49:29 +0100 (Thu, 28 Feb 2019) | 7 lines
[X86] Don't peek through bitcasts before checking ISD::isBuildVectorOfConstantSDNodes in combineTruncatedArithmetic
We don't have any combines that can look through a bitcast to truncate a build vector of constants. So the truncate will stick around and give us something like this pattern (binop (trunc X), (trunc (bitcast (build_vector)))) which has two truncates in it. Which will be reversed by hoistLogicOpWithSameOpcodeHands in the generic DAG combiner. Thus causing an infinite loop.
Even if we had a combine for (truncate (bitcast (build_vector))), I think it would need to be implemented in getNode otherwise DAG combiner visit ordering would probably still visit the binop first and reverse it. Or combineTruncatedArithmetic would need to do its own constant folding.
Differential Revision: https://reviews.llvm.org/D58705
r355117 | ctopper | 2019-02-28 19:50:16 +0100 (Thu, 28 Feb 2019) | 1 line