Hello,
I've had this patch some time now, it's simple and cosmetic only, I
had done it while trying to understand expression costs in CSE. I
think it's more readable than the previous one. FWIW it passed all tests
on x86.
Thanks,
Dimitris
=== modified file 'gcc/cse.c'
--- gcc/cse.c 2012-06-15 09:22:00 +0000
+++ gcc/cse.c 2012-07-08 07:28:52 +0000
@@ -713,32 +713,25 @@ approx_reg_cost (rtx x)
static int
preferable (int cost_a, int regcost_a, int cost_b, int regcost_b)
{
- /* First, get rid of cases involving expressions that are entirely
- unwanted. */
- if (cost_a != cost_b)
- {
- if (cost_a == MAX_COST)
- return 1;
- if (cost_b == MAX_COST)
- return -1;
- }
+ int cost_diff = cost_a - cost_b;
+ int regcost_diff = regcost_a - regcost_b;
- /* Avoid extending lifetimes of hardregs. */
- if (regcost_a != regcost_b)
+ if (cost_diff != 0)
{
- if (regcost_a == MAX_COST)
- return 1;
- if (regcost_b == MAX_COST)
- return -1;
+ /* If none of the expressions are entirely unwanted */
+ if ((cost_a != MAX_COST) && (cost_b != MAX_COST)
+ /* AND only one of the regs is HARD_REG */
+ && (regcost_diff != 0)
+ && ((regcost_a == MAX_COST) || (regcost_b == MAX_COST))
+ )
+ /* Then avoid extending lifetime of HARD_REG */
+ return regcost_diff;
+
+ return cost_diff;
}
- /* Normal operation costs take precedence. */
- if (cost_a != cost_b)
- return cost_a - cost_b;
- /* Only if these are identical consider effects on register pressure. */
- if (regcost_a != regcost_b)
- return regcost_a - regcost_b;
- return 0;
+ /* cost_a == costb, consider effects on register pressure */
+ return regcost_diff;
}
/* Internal function, to compute cost when X is not a register; called
