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8720d89aac
This is effectively re-committing the changes from: rL347917 (D54640) rL348195 (D55126) ...which were effectively reverted here: rL348604 ...because the code had a bug that could induce infinite looping or eventual out-of-memory compilation. The bug was that this code did not guard against transforming opaque constants. More details are in the post-commit mailing list thread for r347917. A reduced test for that is included in the x86 bool-math.ll file. (I wasn't able to reduce a PPC backend test for this, but it was almost the same pattern.) Original commit message for r347917: The motivating case for this is shown in: https://bugs.llvm.org/show_bug.cgi?id=32023 and the corresponding rot16.ll regression tests. Because x86 scalar shift amounts are i8 values, we can end up with trunc-binop-trunc sequences that don't get folded in IR. As the TODO comments suggest, there will be regressions if we extend this (for x86, we mostly seem to be missing LEA opportunities, but there are likely vector folds missing too). I think those should be considered existing bugs because this is the same transform that we do as an IR canonicalization in instcombine. We just need more tests to make those visible independent of this patch. llvm-svn: 348706 |
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