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combine.c (simplify_shift_const): Even if we're sign-extracting... 

* combine.c (simplify_shift_const): Even if we're sign-extracting,
don't discard an ASHIFTRT if we're shifting in a wider mode.

From-SVN: r38648
This commit is contained in:
Alexandre Oliva 2001-01-03 06:47:28 +00:00 committed by Alexandre Oliva
parent 232a132fd6
commit 8f8d8d6e32
2 changed files with 14 additions and 4 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2001-01-03 Alexandre Oliva <aoliva@redhat.com>
* combine.c (simplify_shift_const): Even if we're sign-extracting,
don't discard an ASHIFTRT if we're shifting in a wider mode.
2000-01-02 John David Anglin <dave@hiauly1.hia.nrc.ca>
* toplev.c (rest_of_compilation): Don't print basic block information

13
gcc/combine.c
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@ -1,6 +1,6 @@
/* Optimize by combining instructions for GNU compiler.
Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2000 Free Software Foundation, Inc.
1999, 2000, 2001 Free Software Foundation, Inc.
This file is part of GNU CC.
@ -9130,9 +9130,14 @@ simplify_shift_const (x, code, result_mode, varop, input_count)
break;
case ASHIFTRT:
/* If we are extracting just the sign bit of an arithmetic right
shift, that shift is not needed. */
if (code == LSHIFTRT && count == GET_MODE_BITSIZE (result_mode) - 1)
/* If we are extracting just the sign bit of an arithmetic
right shift, that shift is not needed. However, the sign
bit of a wider mode may be different from what would be
interpreted as the sign bit in a narrower mode, so, if
the result is narrower, don't discard the shift. */
if (code == LSHIFTRT && count == GET_MODE_BITSIZE (result_mode) - 1
&& (GET_MODE_BITSIZE (result_mode)
>= GET_MODE_BITSIZE (GET_MODE (varop))))
{
varop = XEXP (varop, 0);
continue;