target/5728: GCC generated non-optimal code for Hitachi SH-4
michaels@stochastik.rwth-aachen.de
michaels@stochastik.rwth-aachen.de
Tue Feb 19 08:28:00 GMT 2002
>Number: 5728
>Category: target
>Synopsis: GCC generated non-optimal code for Hitachi SH-4
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: unassigned
>State: open
>Class: pessimizes-code
>Submitter-Id: net
>Arrival-Date: Tue Feb 19 07:46:01 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: michaels@stochastik.rwth-aachen.de
>Release: gcc version 3.0.4 20020215 (prerelease)
>Organization:
>Environment:
Debian Linux i686 host
Hitachi SH-4 embedded target
compiler built for sh-elf
>Description:
it seems gcc misses some quite obvious optimizations for Hitachi SH-4, and
it even got worse since V3.0.1. The behaviour described here was verified
with 3.0.3 and 3.0.4 20020215 (prerelease).
Without -frename-registers, an additional unnecessary move is generated.
The superfluous instructions are marked in the included assembly output.
>How-To-Repeat:
sh-elf-gcc -m4 -fomit-frame-pointer -Os -S -frename-registers test1.c
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="sh-gcc.txt"
Content-Disposition: inline; filename="sh-gcc.txt"
typedef unsigned long tU32;
typedef unsigned long long tU64;
tU32 test3(tU32 nus, tU32 mult)
{
tU32 tmp = ((tU64) nus * (tU64) mult)>>32;
return tmp + 1;
}
/opt/cgcc2/bin/sh-elf-gcc -m4 -fomit-frame-pointer -Os -S -frename-registers test1.c
.file "test1.c"
.text
.align 1
.global _test3
.type _test3,@function
_test3:
mov r4,r2 ! this move can be eliminated
nop ! why is this NOP necessary?
dmulu.l r5,r2
sts.l pr,@-r15 ! this can be eliminated - V3.0.1 does this!
lds.l @r15+,pr ! this can be eliminated - V3.0.1 does this!
sts mach,r0
mov r0,r3 ! this move can be eliminated
rts
add #1,r0
.Lfe1:
.size _test3,.Lfe1-_test3
.ident "GCC: (GNU) 3.0.4 20020215 (prerelease)"
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