Branch: refs/heads/blead
Home: https://github.com/Perl/perl5
Commit: cd304e76e0a975a4d5600077b2891ed469708009
https://github.com/Perl/perl5/commit/cd304e76e0a975a4d5600077b2891ed469708009
Author: David Mitchell <da...@iabyn.com>
Date: 2020-08-27 (Thu, 27 Aug 2020)
Changed paths:
M inline.h
Log Message:
-----------
S_lossless_NV_to_IV(): skip Perl_isnan
This inline function was added by v5.31.0-27-g3a019afd6f to consolidate
similar code in several places, like pp_add(). It also avoided undefined
behaviour, as seen by ASan, by no longer unconditionally trying to cast
an NV to IV - ASan would complain when nv was -Inf for example.
However that commit introduced a performance regression into common
numeric operators like pp_and(). This commit partially claws back
performance by skipping the initial test of 'skip if Nan' which called
Perl_isnan(). Instead, except on systems where NAN_COMPARE_BROKEN is
true, it relies on NaN being compared to anything always being false,
and simply rearranges existing conditions nv < IV_MIN etc to be
nv >= IV_MIN so that any NaN comparison will trigger a false return.
This claws back about half the performance loss. The rest seems
unavoidable, since the two range tests for IV_MIN..IV_MAX are an
unavoidable part of avoiding undefined behaviour.
