* [Bug tree-optimization/84407] incorrect constant propagation with -frounding-math
[not found] <bug-84407-4@http.gcc.gnu.org/bugzilla/>
@ 2021-10-27 13:09 ` rguenth at gcc dot gnu.org
2021-10-27 13:28 ` rguenth at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2021-10-27 13:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84407
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed|2018-02-15 00:00:00 |2021-10-27
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
In this bug the issue is int-to-real conversion. Note that apart from
fold_convert_const via build_real_from_int_cst also RTL forwprop
via simplify_const_unary_operation folds this in the wrong way.
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2021-10-27 13:09 ` [Bug tree-optimization/84407] incorrect constant propagation with -frounding-math rguenth at gcc dot gnu.org
@ 2021-10-27 13:28 ` rguenth at gcc dot gnu.org
2021-10-27 17:16 ` joseph at codesourcery dot com
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From: rguenth at gcc dot gnu.org @ 2021-10-27 13:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84407
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 51676
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51676&action=edit
patch
Testing for exact real-to-int / int-to-real conversions is a bit awkward but
maybe I am missing interesting details in real.c that could be exercised here.
Also a question is the behavior on overflow when converting a real to an
integer (IIRC the behavior here is undefined, but we constant fold to the
largest/smallest integer here).
For integer to float conversions is the overflow considered before or after
applying the rounding? That is, are there integer values that invoke
undefined behavior when converted to a real dependent on the rounding mode?
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2021-10-27 13:09 ` [Bug tree-optimization/84407] incorrect constant propagation with -frounding-math rguenth at gcc dot gnu.org
2021-10-27 13:28 ` rguenth at gcc dot gnu.org
@ 2021-10-27 17:16 ` joseph at codesourcery dot com
2021-10-28 9:29 ` rguenth at gcc dot gnu.org
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From: joseph at codesourcery dot com @ 2021-10-27 17:16 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84407
--- Comment #5 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Wed, 27 Oct 2021, rguenth at gcc dot gnu.org via Gcc-bugs wrote:
> Also a question is the behavior on overflow when converting a real to an
> integer (IIRC the behavior here is undefined, but we constant fold to the
> largest/smallest integer here).
We follow Annex F here (so unspecified value rather than undefined - as
discussed in other bugs, any given execution of the conversion in the
abstract machine needs to act as if it does return some value of the
type).
> For integer to float conversions is the overflow considered before or after
> applying the rounding? That is, are there integer values that invoke
> undefined behavior when converted to a real dependent on the rounding mode?
It's fully defined regardless of the value (the appropriately rounded
result is returned, which might be an infinity in case of overflow, or the
largest finite value depending on the rounding mode).
Whether the conversion overflows can indeed depend on the rounding mode
(overflow occurs when a conversion in that rounding mode, with infinite
exponent range, would produce a result with an exponent too large to
represent in the floating-point format). For the IEEE formats and integer
types supported by GCC, the only cases where overflow is possible are for
conversions to _Float16, and from unsigned __int128 to float.
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@ 2021-10-28 9:29 ` rguenth at gcc dot gnu.org
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2021-10-28 13:46 ` rguenth at gcc dot gnu.org
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From: rguenth at gcc dot gnu.org @ 2021-10-28 9:29 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84407
Bug 84407 depends on bug 57245, which changed state.
Bug 57245 Summary: Floating-point constant truncation ignores -frounding-math
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57245
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
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From: cvs-commit at gcc dot gnu.org @ 2021-10-28 13:45 UTC (permalink / raw)
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84407
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:
https://gcc.gnu.org/g:81342e95827f77c0917dd7a9fd54ac9729439c8e
commit r12-4767-g81342e95827f77c0917dd7a9fd54ac9729439c8e
Author: Richard Biener <rguenther@suse.de>
Date: Thu Oct 28 11:38:32 2021 +0200
middle-end/84407 - honor -frounding-math for int to float conversion
This makes us honor -frounding-math for integer to float conversions
and avoid constant folding when such conversion is not exact.
2021-10-28 Richard Biener <rguenther@suse.de>
PR middle-end/84407
* fold-const.c (fold_convert_const): Avoid int to float
constant folding with -frounding-math and inexact result.
* simplify-rtx.c (simplify_const_unary_operation): Likewise
for both float and unsigned_float.
* gcc.dg/torture/fp-uint64-convert-double-1.c: New testcase.
* gcc.dg/torture/fp-uint64-convert-double-2.c: Likewise.
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From: rguenth at gcc dot gnu.org @ 2021-10-28 13:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84407
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
The testcase now is fixed on x86_64.
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