https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79910
Bug ID: 79910
Summary: [7 Regression] wrong code with -O -fweb
Product: gcc
Version: 7.0
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 40892
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40892&action=edit
reduced testcase
Output:
$ x86_64-pc-linux-gnu-gcc -O -fweb 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-245841-checking-yes-rtl-df-extra-nographite-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/7.0.1/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
--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-245841-checking-yes-rtl-df-extra-nographite-amd64
Thread model: posix
gcc version 7.0.1 20170302 (experimental) (GCC)
There seems to be a problem in the combine pass.
Before .combine, there is:
...
(insn 16 14 17 2 (parallel [
(set (reg/v:DI 100 [ bD.1802 ])
(lshiftrt:DI (reg:DI 107)
(reg:QI 110)))
(clobber (reg:CC 17 flags))
]) "testcase.c":11 544 {*lshrdi3_1}
(expr_list:REG_DEAD (reg:QI 110)
(expr_list:REG_DEAD (reg:DI 107)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))))
...
(insn 28 27 30 2 (parallel [
(set (reg:DI 128 [ _6 ])
(minus:DI (reg:DI 111 [ p1D.1798 ])
(reg:DI 119)))
(clobber (reg:CC 17 flags))
]) "testcase.c":12 272 {*subdi_1}
(expr_list:REG_DEAD (reg:DI 119)
(expr_list:REG_DEAD (reg:DI 111 [ p1D.1798 ])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))))
(insn 30 28 31 2 (parallel [
(set (reg:SI 120)
(and:SI (subreg:SI (reg/v:DI 100 [ bD.1802 ]) 0)
(const_int 31 [0x1f])))
(clobber (reg:CC 17 flags))
]) "testcase.c":13 389 {*andsi_1}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))
(insn 31 30 32 2 (set (reg:SI 121)
(const_int 4 [0x4])) "testcase.c":13 82 {*movsi_internal}
(nil))
(insn 32 31 33 2 (parallel [
(set (reg/v:SI 106 [ p2D.1799 ])
(lshiftrt:SI (reg:SI 121)
(subreg:QI (reg:SI 120) 0)))
(clobber (reg:CC 17 flags))
]) "testcase.c":13 542 {*lshrsi3_1}
(expr_list:REG_DEAD (reg:SI 121)
(expr_list:REG_DEAD (reg:SI 120)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_EQUAL (lshiftrt:SI (const_int 4 [0x4])
(subreg:QI (reg:SI 120) 0))
(nil))))))
...
But .combine shows:
...
Trying 27, 28 -> 33:
...
Successfully matched this instruction:
(set (reg:QI 128 [ _6 ])
(plus:QI (subreg:QI (reg:DI 111 [ p1D.1798 ]) 0)
(subreg:QI (reg/v:DI 100 [ bD.1802 ]) 0)))
Successfully matched this instruction:
(set (reg:QI 123 [ p1D.1798 ])
(plus:QI (reg:QI 128 [ _6 ])
(subreg:QI (reg:DI 92 [ _6 ]) 0)))
allowing combination of insns 27, 28 and 33
...
Trying 16, 32 -> 35:
...
Successfully matched this instruction:
(set (reg/v:DI 100 [ bD.1802 ])
(lshiftrt:DI (reg:DI 107)
(reg:QI 110)))
Successfully matched this instruction:
(set (reg:SI 125 [ p2D.1799 ])
(const_int 0 [0]))
allowing combination of insns 16, 32 and 35
...
So after .combine, there is:
...
(insn 28 27 30 2 (parallel [
(set (reg:QI 128 [ _6 ])
(plus:QI (subreg:QI (reg:DI 111 [ p1D.1798 ]) 0)
(subreg:QI (reg/v:DI 100 [ bD.1802 ]) 0)))
(clobber (reg:CC 17 flags))
]) "testcase.c":12 219 {*addqi_1}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_DEAD (reg:DI 111 [ p1D.1798 ])
(nil))))
(note 30 28 31 2 NOTE_INSN_DELETED)
(note 31 30 32 2 NOTE_INSN_DELETED)
(insn 32 31 33 2 (parallel [
(set (reg/v:DI 100 [ bD.1802 ])
(lshiftrt:DI (reg:DI 107)
(reg:QI 110)))
(clobber (reg:CC 17 flags))
]) "testcase.c":13 544 {*lshrdi3_1}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_DEAD (reg:DI 107)
(expr_list:REG_DEAD (reg:QI 110)
(nil)))))
...
--> reg 100 is used in insn 28 before it is set in insn 32.
