This can be used to optimize large multiplications after legalization.
Depends on D29565
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[DAGCombiner] mulhi + 1 never overflow. ClosedPublic Authored by deadalnix on Feb 6 2017, 9:13 AM.
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Comment Actions LGTM.
This revision is now accepted and ready to land.Mar 1 2017, 2:59 PM
Closed by commit rL296711: [DAGCombiner] mulhi + 1 never overflow. (authored by deadalnix). · Explain WhyMar 1 2017, 3:56 PM This revision was automatically updated to reflect the committed changes.
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Diff 87305 lib/CodeGen/SelectionDAG/SelectionDAG.cpp
test/CodeGen/X86/mul-i1024.ll
test/CodeGen/X86/mul-i256.ll
test/CodeGen/X86/mul-i512.ll
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Missing a check for which result you're using from the UMUL_LOHI. (I think this transform is only valid for the high result.)