HomePhabricator

[InstCombine] Properly change GEP type when reassociating loop invariant GEP…

Description

[InstCombine] Properly change GEP type when reassociating loop invariant GEP chains

Summary:
This is a fix to PR37005.

Essentially, rL328539 ([InstCombine] reassociate loop invariant GEP chains to enable LICM) contains a bug
whereby it will convert:
%src = getelementptr inbounds i8, i8* %base, <2 x i64> %val
%res = getelementptr inbounds i8, <2 x i8*> %src, i64 %val2
into:
%src = getelementptr inbounds i8, i8* %base, i64 %val2
%res = getelementptr inbounds i8, <2 x i8*> %src, <2 x i64> %val

By swapping the index operands if the GEPs are in a loop, and %val is loop variant while %val2
is loop invariant.

This fix recreates new GEP instructions if the index operand swap would result in the type
of %src changing from vector to scalar, or vice versa.

Reviewers: sebpop, spatel

Reviewed By: sebpop

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D45287