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| author | Sanjay Patel <spatel@rotateright.com> | 2019-09-25 14:35:02 +0000 |
|---|---|---|
| committer | Sanjay Patel <spatel@rotateright.com> | 2019-09-25 14:35:02 +0000 |
| commit | 6d4ea22e70924da411998edcbdb321bfd3f17545 (patch) | |
| tree | 84b7966c637e95a309134ab2ac71575c655b507e /llvm/docs | |
| parent | b2befe47dc4067416729080bd4531af6197bc265 (diff) | |
| download | bcm5719-llvm-6d4ea22e70924da411998edcbdb321bfd3f17545.tar.gz bcm5719-llvm-6d4ea22e70924da411998edcbdb321bfd3f17545.zip | |
[IR] allow fast-math-flags on phi of FP values (2nd try)
The changes here are based on the corresponding diffs for allowing FMF on 'select':
D61917 <https://reviews.llvm.org/D61917>
As discussed there, we want to have fast-math-flags be a property of an FP value
because the alternative (having them on things like fcmp) leads to logical
inconsistency such as:
https://bugs.llvm.org/show_bug.cgi?id=38086
The earlier patch for select made almost no practical difference because most
unoptimized conditional code begins life as a phi (based on what I see in clang).
Similarly, I don't expect this patch to do much on its own either because
SimplifyCFG promptly drops the flags when converting to select on a minimal
example like:
https://bugs.llvm.org/show_bug.cgi?id=39535
But once we have this plumbing in place, we should be able to wire up the FMF
propagation and start solving cases like that.
The change to RecurrenceDescriptor::AddReductionVar() is required to prevent a
regression in a LoopVectorize test. We are intersecting the FMF of any
FPMathOperator there, so if a phi is not properly annotated, new math
instructions may not be either. Once we fix the propagation in SimplifyCFG, it
may be safe to remove that hack.
Differential Revision: https://reviews.llvm.org/D67564
llvm-svn: 372878
Diffstat (limited to 'llvm/docs')
| -rw-r--r-- | llvm/docs/LangRef.rst | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index 87e1b971605..a38356aa27e 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -10067,7 +10067,7 @@ Syntax: :: - <result> = phi <ty> [ <val0>, <label0>], ... + <result> = phi [fast-math-flags] <ty> [ <val0>, <label0>], ... Overview: """"""""" @@ -10094,6 +10094,12 @@ deemed to occur on the edge from the corresponding predecessor block to the current block (but after any definition of an '``invoke``' instruction's return value on the same edge). +The optional ``fast-math-flags`` marker indicates that the phi has one +or more :ref:`fast-math-flags <fastmath>`. These are optimization hints +to enable otherwise unsafe floating-point optimizations. Fast-math-flags +are only valid for phis that return a floating-point scalar or vector +type. + Semantics: """""""""" |
