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gcse.c (hash_scan_set): Do not pick up a REG_EQUAL value if SRC is a REG. 

2008-05-25  Steven Bosscher  <stevenb.gcc@gmail.com>

	* gcse.c (hash_scan_set): Do not pick up a REG_EQUAL value if
	SRC is a REG.

From-SVN: r135860
This commit is contained in:
Steven Bosscher 2008-05-25 11:58:18 +00:00 committed by Richard Biener
parent dd25a747c9
commit 294707717f
2 changed files with 20 additions and 2 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2008-05-25 Steven Bosscher <stevenb.gcc@gmail.com>
* gcse.c (hash_scan_set): Do not pick up a REG_EQUAL value if
SRC is a REG.
2008-05-25 Alan Modra <amodra@bigpond.net.au>
* c-common.c (strip_array_types): Move function to..

17
gcc/gcse.c
View File

@ -1692,12 +1692,25 @@ hash_scan_set (rtx pat, rtx insn, struct hash_table *table)
unsigned int regno = REGNO (dest);
rtx tmp;
/* See if a REG_NOTE shows this equivalent to a simpler expression.
/* See if a REG_EQUAL note shows this equivalent to a simpler expression.
This allows us to do a single GCSE pass and still eliminate
redundant constants, addresses or other expressions that are
constructed with multiple instructions. */
constructed with multiple instructions.
However, keep the original SRC if INSN is a simple reg-reg move. In
In this case, there will almost always be a REG_EQUAL note on the
insn that sets SRC. By recording the REG_EQUAL value here as SRC
for INSN, we miss copy propagation opportunities and we perform the
same PRE GCSE operation repeatedly on the same REG_EQUAL value if we
do more than one PRE GCSE pass.
Note that this does not impede profitale constant propagations. We
"look through" reg-reg sets in lookup_avail_set. */
note = find_reg_equal_equiv_note (insn);
if (note != 0
&& REG_NOTE_KIND (note) == REG_EQUAL
&& !REG_P (src)
&& (table->set_p
? gcse_constant_p (XEXP (note, 0))
: want_to_gcse_p (XEXP (note, 0))))