| Message ID | 55B0AC26.6010501@arm.com |
|---|---|
| State | New |
| Headers | show |
On Thu, 23 Jul 2015, Kyrill Tkachov wrote: > > On 21/07/15 11:11, Richard Biener wrote: > > On Tue, 21 Jul 2015, Kyrill Tkachov wrote: > > > > > On 21/07/15 08:24, Richard Biener wrote: > > > > On Mon, 20 Jul 2015, Kyrill Tkachov wrote: > > > > > > > > > Hi all, > > > > > > > > > > This patch fixes the PR in question which is a miscompilation of > > > > > gcc.dg/fixed-point/unary.c on arm. > > > > > It just restricts the A - B -> A + (-B) transformation when the type > > > > > is > > > > > fixed-point. > > > > > > > > > > This fixes the testcase for me. > > > > > Is this the right approach? > > > > > > > > > > Bootstrap and test on arm and x86 running. > > > > > > > > > > Ok if testing is clean? > > > > Ok, but I think the fold-const.c code has the same issue, no: > > > > > > > > /* A - B -> A + (-B) if B is easily negatable. */ > > > > if (negate_expr_p (arg1) > > > > && !TYPE_OVERFLOW_SANITIZED (type) > > > > && ((FLOAT_TYPE_P (type) > > > > /* Avoid this transformation if B is a positive > > > > REAL_CST. > > > > */ > > > > && (TREE_CODE (arg1) != REAL_CST > > > > || REAL_VALUE_NEGATIVE (TREE_REAL_CST (arg1)))) > > > > || INTEGRAL_TYPE_P (type))) > > > > return fold_build2_loc (loc, PLUS_EXPR, type, > > > > fold_convert_loc (loc, type, arg0), > > > > fold_convert_loc (loc, type, > > > > negate_expr (arg1))); > > > > > > > > ah, no. The above only applies to float-type and integral-types. > > > > > > > > Thus yes, your patch is ok. Can you double-check the other pattern, > > > > > > > > /* -(A + B) -> (-B) - A. */ > > > > (simplify > > > > (negate (plus:c @0 negate_expr_p@1)) > > > > (if (!HONOR_SIGN_DEPENDENT_ROUNDING (element_mode (type)) > > > > && !HONOR_SIGNED_ZEROS (element_mode (type))) > > > > (minus (negate @1) @0))) > > > > > > > > ? > > > Thanks, committed with r226028. > > > I can add (FLOAT_TYPE_P (type) || INTEGRAL_TYPE_P (type)) to the > > > condition. > > > That would more closely mirror the original logic, right? > > > That passes x86_64 bootstrap and aarch64 testing looks ok. > > Yeah, that works for me, too. > > How about this patch then? > Bootstrapped and tested on x86_64 and aarch64. Hmm. The code already pretty much matches the one in fold-const.c. So what's the actual issue with fixed-point types and -(A + B) -> -B - A iff negate_expr_p says that B can be safely negated? That is, can you add a testcase that fails without the patch? Thanks Richard.
On 23/07/15 12:16, Richard Biener wrote: > On Thu, 23 Jul 2015, Kyrill Tkachov wrote: > >> On 21/07/15 11:11, Richard Biener wrote: >>> On Tue, 21 Jul 2015, Kyrill Tkachov wrote: >>> >>>> On 21/07/15 08:24, Richard Biener wrote: >>>>> On Mon, 20 Jul 2015, Kyrill Tkachov wrote: >>>>> >>>>>> Hi all, >>>>>> >>>>>> This patch fixes the PR in question which is a miscompilation of >>>>>> gcc.dg/fixed-point/unary.c on arm. >>>>>> It just restricts the A - B -> A + (-B) transformation when the type >>>>>> is >>>>>> fixed-point. >>>>>> >>>>>> This fixes the testcase for me. >>>>>> Is this the right approach? >>>>>> >>>>>> Bootstrap and test on arm and x86 running. >>>>>> >>>>>> Ok if testing is clean? >>>>> Ok, but I think the fold-const.c code has the same issue, no: >>>>> >>>>> /* A - B -> A + (-B) if B is easily negatable. */ >>>>> if (negate_expr_p (arg1) >>>>> && !TYPE_OVERFLOW_SANITIZED (type) >>>>> && ((FLOAT_TYPE_P (type) >>>>> /* Avoid this transformation if B is a positive >>>>> REAL_CST. >>>>> */ >>>>> && (TREE_CODE (arg1) != REAL_CST >>>>> || REAL_VALUE_NEGATIVE (TREE_REAL_CST (arg1)))) >>>>> || INTEGRAL_TYPE_P (type))) >>>>> return fold_build2_loc (loc, PLUS_EXPR, type, >>>>> fold_convert_loc (loc, type, arg0), >>>>> fold_convert_loc (loc, type, >>>>> negate_expr (arg1))); >>>>> >>>>> ah, no. The above only applies to float-type and integral-types. >>>>> >>>>> Thus yes, your patch is ok. Can you double-check the other pattern, >>>>> >>>>> /* -(A + B) -> (-B) - A. */ >>>>> (simplify >>>>> (negate (plus:c @0 negate_expr_p@1)) >>>>> (if (!HONOR_SIGN_DEPENDENT_ROUNDING (element_mode (type)) >>>>> && !HONOR_SIGNED_ZEROS (element_mode (type))) >>>>> (minus (negate @1) @0))) >>>>> >>>>> ? >>>> Thanks, committed with r226028. >>>> I can add (FLOAT_TYPE_P (type) || INTEGRAL_TYPE_P (type)) to the >>>> condition. >>>> That would more closely mirror the original logic, right? >>>> That passes x86_64 bootstrap and aarch64 testing looks ok. >>> Yeah, that works for me, too. >> How about this patch then? >> Bootstrapped and tested on x86_64 and aarch64. > Hmm. The code already pretty much matches the one in fold-const.c. > > So what's the actual issue with fixed-point types and > -(A + B) -> -B - A iff negate_expr_p says that B can be > safely negated? > > That is, can you add a testcase that fails without the patch? I don't have such a testcase. If negate_expr_p does what we want here, then I suppose it's redundant and I withdraw the patch. I'm not very familiar with the fold-const.c code... Kyrill > > Thanks > Richard. >
commit d514c81a7965fd24b9d8c294b12179b2369c8aa4
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date: Tue Jul 21 10:18:31 2015 +0100
[match.pd] Restrict -(A + B) -> (-B) - A to integral or float types
diff --git a/gcc/match.pd b/gcc/match.pd
index 3d7b32e..29367f2 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -515,7 +515,8 @@ along with GCC; see the file COPYING3. If not see
/* -(A + B) -> (-B) - A. */
(simplify
(negate (plus:c @0 negate_expr_p@1))
- (if (!HONOR_SIGN_DEPENDENT_ROUNDING (element_mode (type))
+ (if ((FLOAT_TYPE_P (type) || INTEGRAL_TYPE_P (type))
+ && !HONOR_SIGN_DEPENDENT_ROUNDING (element_mode (type))
&& !HONOR_SIGNED_ZEROS (element_mode (type)))
(minus (negate @1) @0)))