Commit Graph

7 Commits

Author SHA1 Message Date
Simon Moll d871ef4e6a [instcombine] remove fsub to fneg hacks; only emit fneg
Summary: Rewrite the fsub-0.0 idiom to fneg and always emit fneg for fp
negation. This also extends the scalarization cost in instcombine for unary
operators to result in the same IR rewrites for fneg as for the idiom.

Reviewed By: cameron.mcinally

Differential Revision: https://reviews.llvm.org/D75467
2020-03-10 16:57:02 +01:00
Sanjay Patel 435cdecdf7 [InstCombine] canonicalize fneg before fmul/fdiv
Reverse the canonicalization of fneg relative to fmul/fdiv. That makes it
easier to implement the transforms (and possibly other fneg transforms) in
1 place because we can always start the pattern match from fneg (either the
legacy binop or the new unop).

There's a secondary practical benefit seen in PR21914 and PR42681:
https://bugs.llvm.org/show_bug.cgi?id=21914
https://bugs.llvm.org/show_bug.cgi?id=42681
...hoisting fneg rather than sinking seems to play nicer with LICM in IR
(although this change may expose analysis holes in the other direction).

1. The instcombine test changes show the expected neutral IR diffs from
   reversing the order.

2. The reassociation tests show that we were missing an optimization
   opportunity to fold away fneg-of-fneg. My reading of IEEE-754 says
   that all of these transforms are allowed (regardless of binop/unop
   fneg version) because:

   "For all other operations [besides copy/abs/negate/copysign], this
   standard does not specify the sign bit of a NaN result."
   In all of these transforms, we always have some other binop
   (fadd/fsub/fmul/fdiv), so we are free to flip the sign bit of a
   potential intermediate NaN operand.
   (If that interpretation is wrong, then we must already have a bug in
   the existing transforms?)

3. The clang tests shouldn't exist as-is, but that's effectively a
   revert of rL367149 (the test broke with an extension of the
   pre-existing fneg canonicalization in rL367146).

Differential Revision: https://reviews.llvm.org/D65399

llvm-svn: 367447
2019-07-31 16:53:22 +00:00
Sanjay Patel e9ee7b47d4 [InstCombine] fold fadd+fneg with fdiv/fmul betweena
The backend already does this via isNegatibleForFree(),
but we may want to alter the fneg IR canonicalizations
that currently exist, so we need to try harder to fold
fneg in IR to avoid regressions.

llvm-svn: 367227
2019-07-29 13:50:25 +00:00
Sanjay Patel 74c35bd6b0 [InstCombine] add tests for fadd with negated operand; NFC
llvm-svn: 367222
2019-07-29 12:49:36 +00:00
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 1170daa277 [InstCombine] simplify fneg+fadd folds; NFC
Two cleanups:
1. As noted in D45453, we had tests that don't need FMF that were misplaced in the 'fast-math.ll' test file.
2. This removes the final uses of dyn_castFNegVal, so that can be deleted. We use 'match' now.

llvm-svn: 330126
2018-04-16 14:13:57 +00:00