https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83424
Bug ID: 83424
Summary: [8 Regression] wrong code with -O -fno-tree-ccp
-fno-tree-coalesce-vars
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: zsojka at seznam dot cz
Target Milestone: ---
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Created attachment 42882
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42882&action=edit
reduced testcase
Output:
$ x86_64-pc-linux-gnu-gcc -O -fno-tree-ccp -fno-tree-coalesce-vars testcase.c
$ ./a.out
Aborted
$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-255624-checking-yes-rtl-df-extra-nobootstrap-nographite-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--disable-bootstrap --without-cloog --without-ppl --without-isl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=x86_64-pc-linux-gnu --with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-255624-checking-yes-rtl-df-extra-nobootstrap-nographite-amd64
Thread model: posix
gcc version 8.0.0 20171214 (experimental) (GCC)
Tested revisions:
r255624 - FAIL
r255606 - FAIL
r255553 - FAIL
r255386 - OK
foo() is optimized to just "retn"
This seems to go wrong in .combine:
...
Trying 21, 11 -> 22:
21: {r112:TI=-r101:TI;clobber flags:CC;}
REG_UNUSED flags:CC
11: r98:QI=~r105:QI
REG_DEAD r105:QI
REG_EQUAL ~[`b']
22: {r113:QI=r98:QI*r112:TI#0;clobber flags:CC;}
REG_DEAD r112:TI
REG_DEAD r98:QI
REG_UNUSED flags:CC
Failed to match this instruction:
(parallel [
(set (reg:QI 113 [ xD.1900 ])
(mult:QI (plus:QI (reg:QI 105 [ bD.1896 ])
(const_int 1 [0x1]))
(subreg:QI (reg/v:TI 101 [ pD.1897 ]) 0)))
(clobber (reg:CC 17 flags))
])
Failed to match this instruction:
(set (reg:QI 113 [ xD.1900 ])
(mult:QI (plus:QI (reg:QI 105 [ bD.1896 ])
(const_int 1 [0x1]))
(subreg:QI (reg/v:TI 101 [ pD.1897 ]) 0)))
Successfully matched this instruction:
(set (reg:QI 112)
(plus:QI (reg:QI 105 [ bD.1896 ])
(const_int 1 [0x1])))
Successfully matched this instruction:
(set (reg:QI 113 [ xD.1900 ])
(mult:QI (reg:QI 112)
(subreg:QI (reg/v:TI 101 [ pD.1897 ]) 0)))
allowing combination of insns 11, 21 and 22
original costs 4 + 8 + 24 = 36
replacement costs 4 + 24 = 28
deferring deletion of insn with uid = 11.
modifying insn i2 21: {r112:QI=r105:QI+0x1;clobber flags:CC;}
REG_UNUSED flags:CC
REG_DEAD r105:QI
deferring rescan insn with uid = 21.
modifying insn i3 22: {r113:QI=r112:QI*r101:TI#0;clobber flags:CC;}
REG_DEAD r101:TI
REG_UNUSED flags:CC
REG_DEAD r112:QI
deferring rescan insn with uid = 22.
...
It seems the REG_DEAD r101:TI note should not be there, this r101 is later used
by insn 29.
