[PATCH] Fix PR61320: disable bswap for unaligned access on SLOW_UNALIGNED_ACCESS targets

["Thomas Preud'homme" <thomas dot preudhomme at arm dot com>]

Hi there,

It seems from PR61320 that the bswap pass causes some problems when it replaces
an OR expression by an unaligned access. Although it's not clear yet why the
unaligned load does not go through the extract_bit_field codepath, it is necessary to
provide a solution as this prevent sparc from bootstrapping. This patch takes the
simple approach of cancelling the bswap optimization when the load that would
replace the OR expression would be an unaligned load and the target has
SLOW_UNALIGNED_ACCESS. In the long run this patch should be reverted as soon
as the root cause of the current problem is found.

The patch also rewrite the test to take into account the fact that the optimization is
not done for some target. It also add some alignment hint so that more tests can be
run even on STRICT_ALIGNMENT targets.

ChangeLog changes are:

*** gcc/ChangeLog ***

2014-06-03  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	PR tree-optimization/61320
	* tree-ssa-math-opts.c (bswap_replace): Cancel bswap optimization when
	load is unaligned and would be slow for this target.

*** gcc/testsuite/ChangeLog ***

2014-06-03  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* gcc.dg/optimize-bswaphi-1.c: Make variables global when possible to
	enforce correct alignment and make the test work better on
	STRICT_ALIGNMENT targets. Also adjust dg-final selectors when alignment
	cannot be controlled (read_*_3 ()).
	* gcc.dg/optimize-bswapsi-2.c: Likewise.
	* gcc.dg/optimize-bswapdi-3.c: Likewise.

Bootstrapped on x86_64-linux-gnu and no regression found in the testsuite. Patch is
in attachment. It applies on top of the one for PR61306 in the email titled
"[PATCH] Fix PR61306: improve handling of sign and cast in bswap" but can be
trivially modified to apply directly on trunk should that patch (PR61306) need to be
improved.

Is this ok for trunk?

Best regards,

Thomas

Attachment: PR61320.1.0.diff
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