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[DAGCombiner] skip reciprocal divisor optimization for x/sqrt(x), better

Authored by spatel on Aug 31 2020, 6:31 AM.

Description

[DAGCombiner] skip reciprocal divisor optimization for x/sqrt(x), better

I tried to fix this in:
rG716e35a0cf53
...but that patch depends on the order that we encounter the
magic "x/sqrt(x)" expression in the combiner's worklist.

This patch should improve that by waiting until we walk the
user list to decide if there's a use to skip.

The AArch64 test reveals another (existing) ordering problem
though - we may try to create an estimate for plain sqrt(x)
before we see that it is part of a 1/sqrt(x) expression.

Details

Committed
spatelAug 31 2020, 6:35 AM
Parents
rG11e0c5b64846: [AArch64] add another test for reciprocal sqrt; NFC
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