Within the M-profile of the Arm architecture, some instructions
admit both a 16-bit and a 32-bit encoding. For those instructions,
some assemblers support the use of the .n (narrow) and .w (wide)
suffixes to force a choice of instruction encoding width.
Forcing the size of encodings may be useful to ensure alignment
of code, which can have a significant performance impact on some
microarchitectures.
It is for this reason that a previous commit introduced explicit
.w suffixes into what was believed to be M-profile only assembly
in library/bn_mul.h.
This change, however, introduced two issues:
First, the assembly block in question is used also for Armv7-A
systems, on which the .n/.w distinction is not meaningful
(all instructions are 32-bit).
Second, compiler support for .n/.w suffixes appears patchy,
leading to compilation failures even when building for M-profile
targets.
This commit removes the .w annotations in order to restore working
code, deferring controlled re-introduction for the sake of performance.
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Description
A few sentences describing the overall goals of the pull request's commits.
Status
READY/IN DEVELOPMENT/HOLD
Requires Backporting
When there is a bug fix, it should be backported to all maintained and supported branches.
Changes do not have to be backported if:
This PR is a new feature\enhancement
This PR contains changes in the API. If this is true, and there is a need for the fix to be backported, the fix should be handled differently in the legacy branch
Yes | NO
Which branch?
Migrations
If there is any API change, what's the incentive and logic for it.
YES | NO
Additional comments
Any additional information that could be of interest
Todos
[ ] Tests
[ ] Documentation
[ ] Changelog updated
[ ] Backported
Steps to test or reproduce
Outline the steps to test or reproduce the PR here.
Within the M-profile of the Arm architecture, some instructions admit both a 16-bit and a 32-bit encoding. For those instructions, some assemblers support the use of the .n (narrow) and .w (wide) suffixes to force a choice of instruction encoding width. Forcing the size of encodings may be useful to ensure alignment of code, which can have a significant performance impact on some microarchitectures.
It is for this reason that a previous commit introduced explicit .w suffixes into what was believed to be M-profile only assembly in library/bn_mul.h.
This change, however, introduced two issues:
This commit removes the .w annotations in order to restore working code, deferring controlled re-introduction for the sake of performance.
Fixes #6089.
Signed-off-by: Hanno Becker hanno.becker@arm.com
Notes:
Signed-off-by:line from the committer to certify that the contribution is made under the terms of the Developer Certificate of Origin.Description
A few sentences describing the overall goals of the pull request's commits.
Status
READY/IN DEVELOPMENT/HOLD
Requires Backporting
When there is a bug fix, it should be backported to all maintained and supported branches. Changes do not have to be backported if:
Yes | NO
Which branch?
Migrations
If there is any API change, what's the incentive and logic for it.
YES | NO
Additional comments
Any additional information that could be of interest
Todos
Steps to test or reproduce
Outline the steps to test or reproduce the PR here.