Hi all, The fix for PR61306 disabled bswap when a sign extension is detected. However this led to a test case regression (and potential performance regression) in case where a sign extension happens but its effect is canceled by other bit manipulation. This patch aims to fix that by having a special marker to track bytes whose value is unpredictable due to sign extension. If the final result of a bit manipulation doesn't contain any such marker then the bswap optimization can proceed.
*** gcc/ChangeLog ***
2014-09-15 Thomas Preud'homme <thomas.preudho...@arm.com>
PR tree-optimization/63266
* tree-ssa-math-opts.c (struct symbolic_number): Add comment about
marker for unknown byte value.
(MARKER_MASK): New macro.
(MARKER_BYTE_UNKNOWN): New macro.
(HEAD_MARKER): New macro.
(do_shift_rotate): Mark bytes with unknown values due to sign
extension when doing an arithmetic right shift. Replace hardcoded
mask for marker by new MARKER_MASK macro.
(find_bswap_or_nop_1): Likewise and adjust ORing of two symbolic
numbers accordingly.
*** gcc/testsuite/ChangeLog ***
2014-09-15 Thomas Preud'homme <thomas.preudho...@arm.com>
PR tree-optimization/63266
* gcc.dg/optimize-bswapsi-1.c (swap32_d): New bswap pass test.
Testing:
* Built an arm-none-eabi-gcc cross-compiler and used it to run the testsuite on
QEMU emulating Cortex-M3 without any regression
* Bootstrapped on x86_64-linux-gnu target and testsuite was run without
regression
Ok for trunk?
pr63266.1.1.diff
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