http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55666
Bug #: 55666
Summary: Use scratch register to avoid save/restore of callee
saved register
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: car...@google.com
Compile the attached source code with options: -march=armv7-a -mthumb -O2
I get the following instructions
YUY2ToUVRow_NEON:
@ args = 4, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
push {r4}
ldr r4, [sp, #4]
#APP
@ 5 "tx.i" 1
adds r1, r0, r1
.p2align 2
1:
vld4.8 {d0, d1, d2, d3}, [r0]!
vld4.8 {d4, d5, d6, d7}, [r1]!
vrhadd.u8 d1, d1, d5
vrhadd.u8 d3, d3, d7
vst1.u8 {d1}, [r2]!
vst1.u8 {d3}, [r3]!
subs r4, r4, #16
bgt 1b
@ 0 "" 2
.thumb
ldr r4, [sp], #4
bx lr
If we replace all usage of r4 with a scratch register r12, then we can avoid
the save/restore of r4.
