[PATCH, rtl-optimization]: Fix PR 45223, RTL PRE GCSE pass hoists trapping insn out of loop

[Uros Bizjak <ubizjak at gmail dot com>]

Hello!

Attached patch fixes wrong hoisting of trapping insns out from the
loop.  As commented in the original PR [1], the problem is in PRE GCSE
pass that does not look if the moved instruction can trap.  The
original problem reliably triggers on targets, where modulo is a
single HW insn (as in case of moxie-elf target), but the problem can
also be shown on x86_64-pc-linux-gnu with slightly modified testcase
[2].

2010-08-07  Uros Bizjak  <ubizjak@gmail.com>

	PR rtl-optimization/45223
	* gcse.c (compute_hash_table_work): Skip insns that may trap when
	building hash table.

The patch was bootstrapped and regression tested on
x86_64-pc-linux-gnu {,-m32} on gcc-4_5 branch. I have also checked
that patched gcc produces correct asm for moxie and for modified FP
case. In the modified FP case, --ffast-math still hoists FP division
out of the loop (allowed by may_trap_p predicate).

H.J. will check the performance effect of the patch on the SPEC, but
--ffast-math compilation seems to be unaffected.

OK for mainline and release branches?

[1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38819#c16
[2] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45223#c2

Uros.

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