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ifcvt.c (noce_get_alt_condition): If the condition is a compare against a constant...

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* ifcvt.c (noce_get_alt_condition): If the condition is a compare
against a constant, try to adjust the compare to have the desired
constant in it so that min/max optimizations happen more often.

From-SVN: r44435
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DJ Delorie 2001-07-27 23:13:34 -04:00 committed by DJ Delorie
parent da397f8ed0
commit 7f64687763
2 changed files with 115 additions and 1 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2001-07-27 DJ Delorie <dj@redhat.com>
* ifcvt.c (noce_get_alt_condition): If the condition is a compare
against a constant, try to adjust the compare to have the desired
constant in it so that min/max optimizations happen more often.
Fri Jul 27 17:53:00 CEST 2001 Jan Hubicka <jh@suse.cz>
* flow.c (last_loop_beg_note): New function.

110
gcc/ifcvt.c
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@ -1,5 +1,5 @@
/* If-conversion support.
Copyright (C) 2000 Free Software Foundation, Inc.
Copyright (C) 2000, 2001 Free Software Foundation, Inc.
This file is part of GNU CC.
@ -1150,6 +1150,114 @@ noce_get_alt_condition (if_info, target, earliest)
= GET_CODE (XEXP (SET_SRC (set), 2)) == LABEL_REF
&& XEXP (XEXP (SET_SRC (set), 2), 0) == JUMP_LABEL (if_info->jump);
/* If we're looking for a constant, try to make the conditional
have that constant in it. There are two reasons why it may
not have the constant we want:
1. GCC may have needed to put the constant in a register, because
the target can't compare directly against that constant. For
this case, we look for a SET immediately before the comparison
that puts a constant in that register.
2. GCC may have canonicalized the conditional, for example
replacing "if x < 4" with "if x <= 3". We can undo that (or
make equivalent types of changes) to get the constants we need
if they're off by one in the right direction. */
if (GET_CODE (target) == CONST_INT)
{
enum rtx_code code = GET_CODE (if_info->cond);
rtx op_a = XEXP (if_info->cond, 0);
rtx op_b = XEXP (if_info->cond, 1);
rtx prev_insn;
/* First, look to see if we put a constant in a register. */
prev_insn = PREV_INSN (if_info->cond_earliest);
if (prev_insn
&& INSN_P (prev_insn)
&& GET_CODE (PATTERN (prev_insn)) == SET)
{
rtx src = find_reg_equal_equiv_note (prev_insn);
if (!src)
src = SET_SRC (PATTERN (prev_insn));
if (GET_CODE (src) == CONST_INT)
{
if (rtx_equal_p (op_a, SET_DEST (PATTERN (prev_insn))))
{
op_a = src;
if_info->cond_earliest = prev_insn;
}
else if (rtx_equal_p (op_b, SET_DEST (PATTERN (prev_insn))))
{
op_b = src;
if_info->cond_earliest = prev_insn;
}
if (GET_CODE (op_a) == CONST_INT)
{
rtx tmp = op_a;
op_a = op_b;
op_b = tmp;
code = swap_condition (code);
}
}
}
/* Now, look to see if we can get the right constant by
adjusting the conditional. */
if (GET_CODE (op_b) == CONST_INT)
{
HOST_WIDE_INT desired_val = INTVAL (target);
HOST_WIDE_INT actual_val = INTVAL (op_b);
switch (code)
{
case LT:
if (actual_val == desired_val + 1)
{
code = LE;
op_b = GEN_INT (desired_val);
}
break;
case LE:
if (actual_val == desired_val - 1)
{
code = LT;
op_b = GEN_INT (desired_val);
}
break;
case GT:
if (actual_val == desired_val - 1)
{
code = GE;
op_b = GEN_INT (desired_val);
}
break;
case GE:
if (actual_val == desired_val + 1)
{
code = GT;
op_b = GEN_INT (desired_val);
}
break;
default:
break;
}
}
/* If we made any changes, generate a new conditional that is
equivalent to what we started with, but has the right
constants in it. */
if (code != GET_CODE (if_info->cond)
|| op_a != XEXP (if_info->cond, 0)
|| op_b != XEXP (if_info->cond, 1))
{
cond = gen_rtx_fmt_ee (code, GET_MODE (cond), op_a, op_b);
*earliest = if_info->cond_earliest;
return cond;
}
}
cond = canonicalize_condition (if_info->jump, cond, reverse,
earliest, target);
if (! cond || ! reg_mentioned_p (target, cond))