https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101257
Bug ID: 101257
Summary: [11/12 Regression] Maybe wrong code since IPA mod ref
was introduced
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: marxin at gcc dot gnu.org
CC: hubicka at gcc dot gnu.org, marxin at gcc dot gnu.org
Target Milestone: ---
It's likely caused by a violation of the strict aliasing rules, but I can't
verify that:
$ wget http://loop-aes.sourceforge.net/aespipe/aespipe-v2.4f.tar.bz2
$ cd aespipe-v2.4f/
$ export CFLAGS="-O2 -flto -flto-partition=one" && ./configure && make tests
...
./aespipe -v -p 3 -e AES128 -K ./gpgkey2.asc -G test-dir1 <test-file3
>test-file1 3<test-file4
./aespipe: C-language AES, 128 key bits, encrypting, multi-key-v2 mode, RAM not
locked
make test-part3
make[2]: Entering directory '/tmp/aespipe-v2.4f'
md5sum test-file1 >test-file2
echo "f9825b79873f5c439ae9371c1a929a6c test-file1" >test-file5
make[2]: Leaving directory '/tmp/aespipe-v2.4f'
cmp test-file2 test-file5
test-file2 test-file5 differ: byte 1, line 1
make[1]: *** [Makefile:120: test-part2] Error 1
make[1]: Leaving directory '/tmp/aespipe-v2.4f'
make: *** [Makefile:87: tests] Error 2
Adding -fno-strict-aliasing fixes that. And the following dbg counter shows
that:
$ gcc -o aespipe aespipe.o aes.o md5.o sha512.o rmd160.o
-fdbg-cnt=ipa_mod_ref:385-385 -flto-partition=one
-fdump-tree-optimized-lineno=bad -fdump-ipa-modref-details && make tests
optimized dump diff is then:
;; Function compute_sector_iv (compute_sector_iv, funcdef_no=0, decl_uid=4504,
cgraph_uid=12, symbol_order=57)
...
[./aespipe.c:775:20] _13 = MEM[(u_int64_t *)bfp_22 + 16B];
[./aespipe.c:775:26] _14 = MEM[(u_int64_t *)bfp_22];
[./aespipe.c:775:20] _15 = _13 ^ _14;
[./aespipe.c:775:20] MEM[(u_int64_t *)bfp_22 + 16B] = _15;
[./aespipe.c:776:20] _16 = MEM[(u_int64_t *)bfp_22 + 24B];
- [./aespipe.c:776:26] _17 = MEM[(u_int64_t *)bfp_22 + 8B];
- [./aespipe.c:776:20] _18 = _16 ^ _17;
+ [./aespipe.c:776:20] _18 = _12 ^ _16;
[./aespipe.c:776:20] MEM[(u_int64_t *)bfp_22 + 24B] = _18;
So one load is optimized out
769 do {
770 bfp[0] ^= dip[0];
771 bfp[1] ^= dip[1];
772 aes_encrypt(acpa[0], (unsigned char *)bfp, (unsigned char
*)bfp);
773 dip = bfp;
774 bfp += 2;
775 bfp[0] ^= dip[0];
776 bfp[1] ^= dip[1];
777 aes_encrypt(acpa[0], (unsigned char *)bfp, (unsigned char
*)bfp);
778 dip = bfp;
779 bfp += 2;
780 } while(--x >= 0);
781 size -= 512;
@Honza: Can you please take a look?
