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aarch64: Improve cost of a ? {-,}1 : b

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While looking into PR 112454, I found the cost for
`(if_then_else (cmp) (const_int 1) (reg))` was being recorded as 8
(or `COSTS_N_INSNS (2)`) but it should have been 4 (or `COSTS_N_INSNS (1)`).
This improves the cost by not adding the cost of `(const_int 1)` to
the total cost.

It does not does not fully fix PR 112454 as that requires other changes to forwprop
the `(const_int 1)` earlier than combine. Though we do fix the loop case where the
constant was only used once.

Bootstrapped and tested on aarch64-linux-gnu with no regressions.

gcc/ChangeLog:

	* config/aarch64/aarch64.cc (aarch64_if_then_else_costs):
	Handle csinv/csinc case of 1/-1.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/csinc-3.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
This commit is contained in:
Andrew Pinski 2023-11-26 23:25:51 +00:00
parent cd2519a6f8
commit d29d27bde5
2 changed files with 22 additions and 0 deletions
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12
gcc/config/aarch64/aarch64.cc
View file

@ -11607,6 +11607,18 @@ aarch64_if_then_else_costs (rtx op0, rtx op1, rtx op2, int *cost, bool speed)
/* CSINV/NEG with zero extend + const 0 (*csinv3_uxtw_insn3). */
op1 = XEXP (inner, 0);
}
else if (op1 == constm1_rtx || op1 == const1_rtx)
{
/* Use CSINV or CSINC. */
*cost += rtx_cost (op2, VOIDmode, IF_THEN_ELSE, 2, speed);
return true;
}
else if (op2 == constm1_rtx || op2 == const1_rtx)
{
/* Use CSINV or CSINC. */
*cost += rtx_cost (op1, VOIDmode, IF_THEN_ELSE, 1, speed);
return true;
}
*cost += rtx_cost (op1, VOIDmode, IF_THEN_ELSE, 1, speed);
*cost += rtx_cost (op2, VOIDmode, IF_THEN_ELSE, 2, speed);

10
gcc/testsuite/gcc.target/aarch64/csinc-3.c Normal file
View file

@ -0,0 +1,10 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fno-tree-vectorize" } */
int f(int *a, int n, int *b, int d)
{
for(int i = 0; i < n; i++)
b[i] = a[i] == 100 ? 1 : d;
/* { dg-final { scan-assembler "csinc\tw\[0-9\].*wzr" } } */
return 0;
}