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During the SeparateConstOffsetFromGEP pass, signed extensions are distributed to the values that feed into them and then later recombined. The recombination stage is somewhat problematic- it doesn't differ add and sub instructions from another when matching the sext(a) +/- sext(b) -> sext(a +/- b) pattern in some instances. An example- the IR contains: %unextendedA %unextendedB %subuAuB = unextendedA - unextendedB %extA = extend A %extB = extend B %addeAeB = extA + extB The problematic optimization will transform that into: %unextendedA %unextendedB %subuAuB = unextendedA - unextendedB %extA = extend A %extB = extend B %addeAeB = extend subuAuB ; Obviously not semantically equivalent to the IR input. This patch fixes that. Patch by Drew Wock <drew.wock@sas.com> Differential Revision: https://reviews.llvm.org/D65967
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