As discussed in PR44330:
https://bugs.llvm.org/show_bug.cgi?id=44330
...the transform from pow(X, -0.5) libcall/intrinsic to
reciprocal square root can result in small deviations from
the expected result due to differences in the pow()
implementation and/or the extra rounding step from the division.
This patch proposes to allow that difference with either the
'approximate functions' or 'reassociate' FMF:
http://llvm.org/docs/LangRef.html#fast-math-flags
In practice, this likely means that the code is compiled with
all of 'fast' (-ffast-math), but I have preserved the existing
specializations for -0.0/-INF that enable generating safe code
if those special values are allowed simultaneously with
allowing approximation/reassociation.
The question about whether a similar restriction is needed for
the non-reciprocal case -- pow(X, 0.5) -- is deferred. That
transform is allowed without FMF currently, and this patch does
not change that behavior.
Differential Revision: https://reviews.llvm.org/D71706
This is a minimal start to correcting a problem most directly discussed in PR38086:
https://bugs.llvm.org/show_bug.cgi?id=38086
We have been hacking around a limitation for FP select patterns by using the
fast-math-flags on the condition of the select rather than the select itself.
This patch just allows FMF to appear with the 'select' opcode. No changes are
needed to "FPMathOperator" because it already includes select-of-FP because
that definition is based on the (return) value type.
Once we have this ability, we can start correcting and adding IR transforms
to use the FMF on a 'select' instruction. The instcombine and vectorizer test
diffs only show that the IRBuilder change is behaving as expected by applying
an FMF guard value to 'select'.
For reference:
rL241901 - allowed FMF with fcmp
rL255555 - allowed FMF with FP calls
Differential Revision: https://reviews.llvm.org/D61917
llvm-svn: 361401
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
Expand the number of cases when `pow(x, 0.5)` is simplified into `sqrt(x)`
by considering the math semantics with more granularity.
Differential revision: https://reviews.llvm.org/D50036
llvm-svn: 339887
As the first test shows, we could transform an llvm intrinsic which never sets errno
into a libcall which could set errno (even though it's marked readnone?), so that's
not ideal.
It's possible that we can also transform a libcall which could set errno to an
intrinsic given the fast-math-flags constraint, but that's deferred to determine
exactly which set of FMF are needed.
Differential Revision: https://reviews.llvm.org/D40150
llvm-svn: 318628
Hal pointed out that the semantic of our intrinsic and the libc
call are slightly different. Add a comment while I'm here to
explain why we can't emit an intrinsic. Thanks Hal!
llvm-svn: 278200
Sanjay Patel