Commit Graph

2 Commits

Author SHA1 Message Date
Roman Lebedev ccf1a5f4bb
[InstCombine] dropRedundantMaskingOfLeftShiftInput(): truncation (PR42563)
Summary:
That fold keeps growing and growing :(
I think this may be one of the last pieces for it.

Since D67677/D67725, the fold knowns the general form
of the pattern - where some masking is needed:
https://rise4fun.com/Alive/F5R
https://rise4fun.com/Alive/gslRa

But there is one more huge piece missing - if you are extracting some bits,
it is not impossible that the origin is wider than the extraction,
i.e. there may be a truncation. And we don't deal with that yet.

But we can, and the generalization remains fully identical:
https://rise4fun.com/Alive/Uar
https://rise4fun.com/Alive/5SW

After a preparatory cleanup i think the diff looks rather clean.

One missing piece is that in some patterns (especially pat. b),
`-1` only needs to be `-1` in final type, but that is for later..

https://bugs.llvm.org/show_bug.cgi?id=42563

Reviewers: spatel, nikic

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69125
2019-11-05 12:41:26 +03:00
Roman Lebedev 08de59bed5 [NFC][InstCombine] Tests for "fold variable mask before variable shift-of-trunc" (PR42563)
https://bugs.llvm.org/show_bug.cgi?id=42563

llvm-svn: 375135
2019-10-17 17:20:12 +00:00