#206 - tree-optimization/114502 - final value replacement for idempotent negation - gcc/gcc - Sourceware Forge: Core Toolchain and Developer Tools

Rachit commented

2026-07-30 10:55:55 +00:00

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SCEV cannot represent a period-2 recurrence, so recognize loops of the
form 'c = -c' with a constant trip count in the final-value replacement
and replace the exit value by c or -c depending on the parity of the trip
count. Bail out when signed overflow must trap (-ftrapv) or be sanitized,
mirroring the existing bitop special-cases.

Tested on aarch64-linux-gnu: gcc.dg/tree-ssa/scev-negate-{1,2,3}.c all pass.

PR tree-optimization/114502

gcc/ChangeLog:

	* tree-scalar-evolution.cc (analyze_and_compute_negate_effect): New.
	(final_value_replacement_loop): Call it.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/scev-negate-1.c: New test.
	* gcc.dg/tree-ssa/scev-negate-2.c: New test.
	* gcc.dg/tree-ssa/scev-negate-3.c: New test.

Signed-off-by: Rachit Mehta rachit.mehta@oss.qualcomm.com

CC: andrew.pinski@oss.qualcomm.com

SCEV cannot represent a period-2 recurrence, so recognize loops of the form 'c = -c' with a constant trip count in the final-value replacement and replace the exit value by c or -c depending on the parity of the trip count. Bail out when signed overflow must trap (-ftrapv) or be sanitized, mirroring the existing bitop special-cases. Tested on aarch64-linux-gnu: gcc.dg/tree-ssa/scev-negate-{1,2,3}.c all pass. PR tree-optimization/114502 ``` gcc/ChangeLog: * tree-scalar-evolution.cc (analyze_and_compute_negate_effect): New. (final_value_replacement_loop): Call it. gcc/testsuite/ChangeLog: * gcc.dg/tree-ssa/scev-negate-1.c: New test. * gcc.dg/tree-ssa/scev-negate-2.c: New test. * gcc.dg/tree-ssa/scev-negate-3.c: New test. ``` Signed-off-by: Rachit Mehta <rachit.mehta@oss.qualcomm.com> CC: andrew.pinski@oss.qualcomm.com

forge-bot commented

2026-07-30 10:55:57 +00:00

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Hi @Rachit. This bot helps send your PR as a patch series to the mailing list. ## Next steps 1. Write a clear PR description. It will be used as the cover letter. 2. To CC extra people, add lines like this **at the end** of the PR description: `CC: Reviewer1 <revi.ewer@example.com>, Reviewer2 <an.other@example.com>`. 3. To preview the emails, comment with `/preview`. 4. When ready, request review in the Reviewers section. Or, if you just want to send the series, comment with `/submit`. 5. Use the cover-letter links below to follow replies. 6. For a new patch series, push your changes, update the PR description with a `Changes since vX` section, and comment with `/submit` again. See [Submitting Patches](https://gcc.gnu.org/contribute.html#patches) and [UsingForge](https://gcc.gnu.org/wiki/UsingForge). Consider joining the [gcc and gcc-patches mailing lists.](https://gcc.gnu.org/lists.html). For real time communication, check the [gcc irc channels](https://gcc.gnu.org/wiki/GCConIRC). Or join [`#overseers`](https://web.libera.chat/#overseers) on Libera Chat, particularly if this automation is not working (stay online to get replies, IRC does not save messages if people are not online).

Rachit force-pushed PR-114502 from f4ed39865e

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2026-07-31 04:41:10 +00:00

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Rachit commented

2026-08-06 10:55:52 +00:00

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/preview

forge-bot commented

2026-08-06 10:55:58 +00:00

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Sent patch series version 1 containing 1 patches to @Rachit's email address.
Message Id of cover message is <bmm.hl37e3q6mi.gcc.gcc.Rachit.206.1.0@forge-stage.sourceware.org>.

Sent patch series version 1 containing 1 patches to @Rachit's email address. Message Id of cover message is `<bmm.hl37e3q6mi.gcc.gcc.Rachit.206.1.0@forge-stage.sourceware.org>`.

Rachit commented

2026-08-06 11:05:30 +00:00

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/submit

forge-bot commented

2026-08-06 11:06:01 +00:00

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Version 1 of this pull request has been stored. It includes the following commits:

tree-optimization/114502 - final value replacement for idempotent negation - 7bda01c9f0

Version 1 of this pull request has been stored. It includes the following commits: - tree-optimization/114502 - final value replacement for idempotent negation - 7bda01c9f0fd3d2a364363a351cfec966b0bb511

forge-bot commented

2026-08-06 11:06:01 +00:00

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Pull Request versions:

#	Base	Head
1	`e873aac49e`	`7bda01c9f0`	(diff)

In order to compare , clone this repository and run

PR=206
git fetch origin "refs/versioned_pull/${PR}/*:refs/versioned_pull/${PR}/*"
PRV1=1
PRV2=2
git range-diff "refs/versioned_pull/${PR}/${PRV1}/base..refs/versioned_pull/${PR}/${PRV1}/head"  "refs/versioned_pull/${PR}/${PRV2}/base..refs/versioned_pull/${PR}/${PRV2}/head"

Pull Request versions: | # | Base | Head | | | - | ---- | ---- | - | | 1 | e873aac49eb2b58ae18e05f4150826278bdbb3cb | 7bda01c9f0fd3d2a364363a351cfec966b0bb511 | [(diff)](https://forge.sourceware.org/gcc/gcc.git/compare/e873aac49eb2b58ae18e05f4150826278bdbb3cb...7bda01c9f0fd3d2a364363a351cfec966b0bb511) | In order to compare , clone this repository and run ``` PR=206 git fetch origin "refs/versioned_pull/${PR}/*:refs/versioned_pull/${PR}/*" PRV1=1 PRV2=2 git range-diff "refs/versioned_pull/${PR}/${PRV1}/base..refs/versioned_pull/${PR}/${PRV1}/head" "refs/versioned_pull/${PR}/${PRV2}/base..refs/versioned_pull/${PR}/${PRV2}/head" ```

forge-bot commented

2026-08-06 11:06:30 +00:00

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Sent patch series version 1 containing 1 patches to gcc-patches mailing list gcc-patches@gcc.gnu.org and cc'd andrew.pinski@oss.qualcomm.com.
Cover letter

Sent patch series version 1 containing 1 patches to gcc-patches mailing list <gcc-patches@gcc.gnu.org> and cc'd andrew.pinski@oss.qualcomm.com. [Cover letter](https://inbox.sourceware.org/gcc-patches/bmm.hl37nocx96.gcc.gcc.Rachit.206.1.0@forge-stage.sourceware.org)

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