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[TargetLower] Update shouldFormOverflowOp check if math is used.

Authored by fhahn on Feb 17 2020, 8:26 AM.



On some targets, like SPARC, forming overflow ops is only profitable if
the math result is used:
This patch adds a new MathUsed parameter to allow the targets
to make the decision and defaults to only allowing it
if the math result is used. That is the conservative choice.

This patch also updates AArch64ISelLowering and X86ISelLowering to all
forming overflow ops if the math result is not used. On those targets
using the overflow intrinsic for the overflow check only generates
better code.

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fhahn created this revision.Feb 17 2020, 8:26 AM
Herald added a project: Restricted Project. · View Herald TranscriptFeb 17 2020, 8:26 AM
lebedev.ri accepted this revision.Feb 17 2020, 2:58 PM
lebedev.ri edited the summary of this revision. (Show Details)

LG to me.

This revision is now accepted and ready to land.Feb 17 2020, 2:59 PM
This revision was automatically updated to reflect the committed changes.