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From: gcc-patches-ow...@gcc.gnu.org <gcc-patches-ow...@gcc.gnu.org> on behalf
of Tamar Christina <tamar.christ...@arm.com>
Sent: Tuesday, May 2, 2017 4:37:12 PM
To: GCC Patches
Cc: nd; Kyrylo Tkachov; Ramana Radhakrishnan; Richard Earnshaw; ni...@redhat.com
Subject: [PATCH][GCC][ARM] Adjust costs so udiv is preferred over sdiv when
both are valid. [Patch (2/2)]
Hi All,
This patch adjusts the cost model so that when both sdiv and udiv are possible
it prefers udiv over sdiv. This was done by making sdiv slightly more expensive
instead of making udiv cheaper to keep the baseline costs of a division the same
as before.
Similar to aarch64 this patch along with my other two related mid-end changes
makes a big difference in division by constants.
Given:
int f2(int x)
{
return ((x * x) % 300) + ((x * x) / 300);
}
we now generate
f2:
mul r3, r0, r0
mov r0, r3
ldr r1, .L3
umull r2, r3, r0, r1
lsr r2, r3, #5
add r3, r2, r2, lsl #2
rsb r3, r3, r3, lsl #4
sub r0, r0, r3, lsl #2
add r0, r0, r2
bx lr
as opposed to
f2:
mul r3, r0, r0
mov r0, r3
ldr r3, .L4
push {r4, r5}
smull r4, r5, r0, r3
asr r3, r0, #31
rsb r3, r3, r5, asr #5
add r2, r3, r3, lsl #2
rsb r2, r2, r2, lsl #4
sub r0, r0, r2, lsl #2
add r0, r0, r3
pop {r4, r5}
bx lr
Bootstrapped and reg tested on arm-none-eabi
with no regressions.
OK for trunk?
Thanks,
Tamar
gcc/
2017-05-02 Tamar Christina <tamar.christ...@arm.com>
* config/arm/arm.c (arm_rtx_costs_internal): Make sdiv more expensive
than udiv.
gcc/testsuite/
2017-05-02 Tamar Christina <tamar.christ...@arm.com>
* gcc.target/arm/sdiv_costs_1.c: New.
