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[CodeGenPrepare] limit formation of overflow intrinsics (PR41129)

Description

[CodeGenPrepare] limit formation of overflow intrinsics (PR41129)

This is probably a bigger limitation than necessary, but since we don't have any evidence yet
that this transform led to real-world perf improvements rather than regressions, I'm making a
quick, blunt fix.

In the motivating x86 example from:
https://bugs.llvm.org/show_bug.cgi?id=41129
...and shown in the regression test, we want to avoid an extra instruction in the dominating
block because that could be costly.

The x86 LSR test diff is reversing the changes from D57789. There's no evidence that 1 version
is any better than the other yet.

Differential Revision: https://reviews.llvm.org/D59602

Details

Committed
spatelMar 21 2019, 6:57 AM
Differential Revision
D59602: [CodeGenPrepare] limit formation of overflow intrinsics (PR41129)
Parents
rL356664: [llvm-readobj] Format codes. NFC.
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