Commit Graph

5 Commits

Author SHA1 Message Date
Eric Christopher cee313d288 Revert "Temporarily Revert "Add basic loop fusion pass.""
The reversion apparently deleted the test/Transforms directory.

Will be re-reverting again.

llvm-svn: 358552
2019-04-17 04:52:47 +00:00
Eric Christopher a863435128 Temporarily Revert "Add basic loop fusion pass."
As it's causing some bot failures (and per request from kbarton).

This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.

llvm-svn: 358546
2019-04-17 02:12:23 +00:00
Sanjay Patel e7b6654711 [InstCombine] refine select-of-constants to bitwise ops
Add logic for the special case when a cmp+select can clearly be
reduced to just a bitwise logic instruction, and remove an 
over-reaching chunk of general purpose bit magic. The primary goal 
is to remove cases where we are not improving the IR instruction 
count when doing these select transforms, and in all cases here that 
is true.

In the motivating 3-way compare tests, there are further improvements
because we can combine/propagate select values (not sure if that
belongs in instcombine, but it's there for now).

DAGCombiner has folds to turn some of these selects into bit magic,
so there should be no difference in the end result in those cases.
Not all constant combinations are handled there yet, however, so it
is possible that some targets will see more cmov/csel codegen with
this change in IR canonicalization. 

Ideally, we'll go further to *not* turn selects into multiple 
logic/math ops in instcombine, and we'll canonicalize to selects.
But we should make sure that this step does not result in regressions
first (and if it does, we should fix those in the backend).

The general direction for this change was discussed here:
http://lists.llvm.org/pipermail/llvm-dev/2016-September/105373.html
http://lists.llvm.org/pipermail/llvm-dev/2017-July/114885.html

Alive proofs for the new bit magic:
https://rise4fun.com/Alive/XG7

Differential Revision: https://reviews.llvm.org/D46086

llvm-svn: 331486
2018-05-03 21:58:44 +00:00
Sanjay Patel 0387ceb67a [InstCombine] add tests for select to logic folds; NFC
As discussed in D45862, we want these folds sometimes
because they're good improvements.
But as we can see here, the current logic doesn't
check uses and doesn't produce optimal code in all
cases. 

llvm-svn: 330837
2018-04-25 15:59:23 +00:00
Sanjay Patel 54795bb16b [InstCombine] move tests for select with bit-test of condition; NFC
These are all but 1 of the select-of-constant tests that appear 
to be transformed within foldSelectICmpAnd() and the block above 
it predicated by decomposeBitTestICmp().

As discussed in D45862 (and can be seen in several tests here),
we probably want to stop doing those transforms because they
can increase the instruction count without benefitting other
passes or codegen.

The 1 test not included here is a urem test where the bit hackery
allows us to remove a urem. To preserve killing that urem, we 
should do some stronger known-bits analysis or pattern matching of 
'urem x, (select-of-pow2-constants)'.

llvm-svn: 330768
2018-04-24 21:06:06 +00:00