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reg-stack.c (change_stack): Improve algorithm used to pop regs off the stack to maximize ffreep usage and...

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* reg-stack.c (change_stack): Improve algorithm used to pop regs
	off the stack to maximize ffreep usage and reduce fxch count.

From-SVN: r91506
This commit is contained in:
Roger Sayle 2004-11-30 02:34:56 +00:00 committed by Roger Sayle
parent c54d30fae2
commit 0cc5dec18a
2 changed files with 65 additions and 4 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2004-11-29 Roger Sayle <roger@eyesopen.com>
* reg-stack.c (change_stack): Improve algorithm used to pop regs
off the stack to maximize ffreep usage and reduce fxch count.
2004-11-30 James A. Morrison <phython@gcc.gnu.org>
PR middle-end/18596

64
gcc/reg-stack.c
View File

@ -2367,10 +2367,66 @@ change_stack (rtx insn, stack old, stack new, enum emit_where where)
/* Pop any registers that are not needed in the new block. */
for (reg = old->top; reg >= 0; reg--)
if (! TEST_HARD_REG_BIT (new->reg_set, old->reg[reg]))
emit_pop_insn (insn, old, FP_MODE_REG (old->reg[reg], DFmode),
EMIT_BEFORE);
/* If the destination block's stack already has a specified layout
and contains two or more registers, use a more intelligent algorithm
to pop registers that minimizes the number number of fxchs below. */
if (new->top > 0)
{
bool slots[REG_STACK_SIZE];
int pops[REG_STACK_SIZE];
int next, dest;
/* First pass to determine the free slots. */
for (reg = 0; reg <= new->top; reg++)
slots[reg] = TEST_HARD_REG_BIT (new->reg_set, old->reg[reg]);
/* Second pass to allocate preferred slots. */
for (reg = old->top; reg > new->top; reg--)
if (TEST_HARD_REG_BIT (new->reg_set, old->reg[reg]))
{
dest = -1;
for (next = 0; next <= new->top; next++)
if (!slots[next] && new->reg[next] == old->reg[reg])
{
slots[next] = true;
dest = next;
break;
}
pops[reg] = dest;
}
else
pops[reg] = reg;
/* Third pass allocates remaining slots and emits pop insns. */
next = 0;
for (reg = old->top; reg > new->top; reg--)
{
dest = pops[reg];
if (dest == -1)
{
/* Find next free slot. */
while (slots[next])
next++;
dest = next++;
}
emit_pop_insn (insn, old, FP_MODE_REG (old->reg[dest], DFmode),
EMIT_BEFORE);
}
}
else
/* The following loop attempts to maximize the number of times we
pop the top of the stack, as this permits the use of the faster
ffreep instruction on platforms that support it. */
for (reg = 0; reg <= old->top; reg++)
if (! TEST_HARD_REG_BIT (new->reg_set, old->reg[reg]))
{
while (old->top > reg
&& ! TEST_HARD_REG_BIT (new->reg_set, old->reg[old->top]))
emit_pop_insn (insn, old, FP_MODE_REG (old->reg[old->top], DFmode),
EMIT_BEFORE);
emit_pop_insn (insn, old, FP_MODE_REG (old->reg[reg], DFmode),
EMIT_BEFORE);
}
if (new->top == -2)
{