gcc 4.5.0 $ cat /tmp/bug.c extern int printf(const char *fmt, ...); void foo(void *x) { printf("%p\n", x); } void bar(long long *x) { printf("%lld ", *x); foo(x); } int main() { bar(&(long long){0ll}); bar(&(long long){1ll}); bar(&(long long){2ll}); bar(&(long long){3ll}); bar(&(long long){4ll}); bar(&(long long){5ll}); bar(&(long long){6ll}); bar(&(long long){7ll}); bar(&(long long){8ll}); bar(&(long long){9ll}); bar(&(long long){10ll}); bar(&(long long){11ll}); bar(&(long long){12ll}); bar(&(long long){13ll}); bar(&(long long){14ll}); bar(&(long long){15ll}); bar(&(long long){16ll}); bar(&(long long){17ll}); bar(&(long long){18ll}); bar(&(long long){19ll}); bar(&(long long){20ll}); bar(&(long long){21ll}); bar(&(long long){22ll}); bar(&(long long){23ll}); bar(&(long long){24ll}); bar(&(long long){25ll}); bar(&(long long){26ll}); bar(&(long long){27ll}); bar(&(long long){28ll}); bar(&(long long){29ll}); bar(&(long long){30ll}); bar(&(long long){31ll}); bar(&(long long){32ll}); bar(&(long long){33ll}); bar(&(long long){34ll}); bar(&(long long){35ll}); bar(&(long long){36ll}); bar(&(long long){37ll}); bar(&(long long){38ll}); bar(&(long long){39ll}); bar(&(long long){40ll}); bar(&(long long){41ll}); bar(&(long long){42ll}); bar(&(long long){43ll}); bar(&(long long){44ll}); return 0; } $ cc -mcpu=cortex-a8 -mfpu=neon -mfloat-abi=softfp -S -O2 /tmp/bug.c inspect bug.s. for a while gcc emits correct instructions: ... mov r2, #29 mov r3, #0 strd r2, [r0, #-240]! bl bar add r0, sp, #360 mov r2, #30 mov r3, #0 strd r2, [r0, #-248]! bl bar however when reaching offset -256, it emits LDRs instead of STRs: add r0, sp, #360 mov r2, #31 mov r3, #0 ldr r2, [r0, #-256]! ldr r3, [r0, #4] bl bar the issue seems to be a typo in gcc/config/arm/arm.c:output_move_double() introduced by commit [1]. i've tried to fix by applying the following: --- ../gcc-4.5.0/gcc/config/arm/arm.c.orig 2010-07-27 14:22:42.000000000 +0300 +++ ../gcc-4.5.0/gcc/config/arm/arm.c 2010-07-27 14:23:05.000000000 +0300 @@ -12182,13 +12182,13 @@ output_move_double (rtx *operands) { if (GET_CODE (XEXP (operands[0], 0)) == PRE_MODIFY) { - output_asm_insn ("ldr%?\t%0, [%1, %2]!", otherops); - output_asm_insn ("ldr%?\t%H0, [%1, #4]", otherops); + output_asm_insn ("str%?\t%0, [%1, %2]!", otherops); + output_asm_insn ("str%?\t%H0, [%1, #4]", otherops); } else { - output_asm_insn ("ldr%?\t%H0, [%1, #4]", otherops); - output_asm_insn ("ldr%?\t%0, [%1], %2", otherops); + output_asm_insn ("str%?\t%H0, [%1, #4]", otherops); + output_asm_insn ("str%?\t%0, [%1], %2", otherops); } } else if (GET_CODE (XEXP (operands[0], 0)) == PRE_MODIFY) [1] http://repo.or.cz/w/official-gcc.git/commitdiff/f1225f6f0f9b7acb3a64314f2113807ebeea5abf?hp=78f46d4510475cdb9532b10787e82b476c9eeef1
Patches should be submitted to gcc-patches@gcc.gnu.org after having been regression tested. Please also submit a testcase and appropriate Changelog entries as documented here - http://gcc.gnu.org/contribute.html#patches Having said that however, this patch looks alright to me from the naked eye and code inspection.
Created attachment 21327 [details] simplified testcase Confirmed with gcc 4.5.0 here. Also tried but could not reproduce the problem with gcc 4.4 (it just does not seem to be able to emit ldrd/strd instructions with pre/post increment).
(In reply to comment #2) > Created an attachment (id=21327) [edit] > simplified testcase Update this test case a little bit, with test commands. Post patch here http://gcc.gnu.org/ml/gcc-patches/2010-08/msg00001.html
> Post patch here http://gcc.gnu.org/ml/gcc-patches/2010-08/msg00001.html + output_asm_insn ("strr%?\t%H0, [%1, #4]", otherops); s/strr/str/ ?
(In reply to comment #4) > > Post patch here http://gcc.gnu.org/ml/gcc-patches/2010-08/msg00001.html > > + output_asm_insn ("strr%?\t%H0, [%1, #4]", otherops); > > s/strr/str/ ? > Right, it is a typo. Latest patch is posted here, http://gcc.gnu.org/ml/gcc-patches/2010-08/msg00018.html
Subject: Bug 45094 Author: qiyao Date: Wed Aug 18 12:33:43 2010 New Revision: 163338 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=163338 Log: gcc/ PR target/45094 * config/arm/arm.c (output_move_double): Fix typo generating instructions ('ldr'->'str'). gcc/testsuite/ PR target/45094 * gcc.target/arm/pr45094.c: New test. Added: trunk/gcc/testsuite/gcc.target/arm/pr45094.c Modified: trunk/gcc/ChangeLog trunk/gcc/config/arm/arm.c trunk/gcc/testsuite/ChangeLog
can this be backported to the 4.5 branch please ?
GCC 4.5.2 is being released, adjusting target milestone.
Can this bug get a "[4.5 regression]" header please? Even though the bug existed in gcc sources since 2007 (see the link in comment 1), the reported wrong-code problem itself was apparently latent until gcc 4.5, and is not reproducible with older gcc versions.
(In reply to comment #9) > see the link in comment 1 Sorry, I mean the link in the original report from Akos: http://repo.or.cz/w/official-gcc.git/commitdiff/f1225f6f
Patch to backport it to 4.5 is here http://gcc.gnu.org/ml/gcc-patches/2010-12/msg01858.html
Is that first hunk intentional?
(In reply to comment #12) > Is that first hunk intentional? No. It is from another PR backport, so it is redundant here. Submit a clean patch again http://gcc.gnu.org/ml/gcc-patches/2010-12/msg01873.html
Fixed in 4.6.0.