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re PR rtl-optimization/45903 (unnecessary load of 32/64bit variable when only 8 bits are needed) 

PR tree-optimization/45903
	* simplify-rtx.c (simplify_subreg): Optimize lowpart SUBREG
	of *SHIFTRT of MEM.

	* gcc.target/i386/pr45903.c: New test.

From-SVN: r165200
This commit is contained in:
Jakub Jelinek 2010-10-08 22:49:19 +02:00 committed by Jakub Jelinek
parent 0fd76d8e4c
commit 509dd3804c
3 changed files with 36 additions and 0 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2010-10-08 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/45903
* simplify-rtx.c (simplify_subreg): Optimize lowpart SUBREG
of *SHIFTRT of MEM.
2010-10-08 Richard Guenther <rguenther@suse.de>
* lto-streamer-in.c (lto_input_ts_decl_minimal_tree_pointers):

25
gcc/simplify-rtx.c
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@ -5482,6 +5482,31 @@ simplify_subreg (enum machine_mode outermode, rtx op,
: byte + shifted_bytes));
}
/* If we have a lowpart SUBREG of a right shift of MEM, make a new MEM
and try replacing the SUBREG and shift with it. Don't do this if
the MEM has a mode-dependent address or if we would be widening it. */
if ((GET_CODE (op) == LSHIFTRT
|| GET_CODE (op) == ASHIFTRT)
&& MEM_P (XEXP (op, 0))
&& CONST_INT_P (XEXP (op, 1))
&& GET_MODE_SIZE (outermode) < GET_MODE_SIZE (GET_MODE (op))
&& (INTVAL (XEXP (op, 1)) % GET_MODE_BITSIZE (outermode)) == 0
&& INTVAL (XEXP (op, 1)) > 0
&& INTVAL (XEXP (op, 1)) < GET_MODE_BITSIZE (innermode)
&& ! mode_dependent_address_p (XEXP (XEXP (op, 0), 0))
&& ! MEM_VOLATILE_P (XEXP (op, 0))
&& byte == subreg_lowpart_offset (outermode, innermode)
&& (GET_MODE_SIZE (outermode) >= UNITS_PER_WORD
|| WORDS_BIG_ENDIAN == BYTES_BIG_ENDIAN))
{
int shifted_bytes = INTVAL (XEXP (op, 1)) / BITS_PER_UNIT;
return adjust_address_nv (XEXP (op, 0), outermode,
(WORDS_BIG_ENDIAN
? byte - shifted_bytes
: byte + shifted_bytes));
}
return NULL_RTX;
}

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2010-10-08 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/45903
* gcc.target/i386/pr45903.c: New test.
2010-10-08 Arnaud Charlet <charlet@adacore.com>
* gnat.dg/interface5.adb: Compile with warnings disabled.