On Sparc Solaris, the attached code leads to the following assembly sequence
being produced at the beginning of a function. Stack slot %fp-32 is read before
it is written. Turning off either -fstrict-aliasing or -fsched-insns causes the
problem to go away.
I'm relying on the GCC extension that allows type punning via unions, and
assuming a big endian layout of all the datatypes. As specified by the
-fstrict-aliasing documentation, I'm copying the value out of the union rather
than taking an address of a union member.
0: 9d e3 bf 80 save %sp, -128, %sp
4: d6 07 bf e4 ld [ %fp + -28 ], %o3
8: c2 07 bf e0 ld [ %fp + -32 ], %g1
c: c2 27 bf e8 st %g1, [ %fp + -24 ]
10: 19 00 00 20 sethi %hi(0x8000), %o4
14: 1b 3f ff ff sethi %hi(0xfffffc00), %o5
18: 9a 13 63 ff or %o5, 0x3ff, %o5 ! ffffffff <main+0xffffffa3>
1c: d8 3f bf e0 std %o4, [ %fp + -32 ]
g++-3_4_3 -v -save-temps -O1 -c -o u64solrs.o u64solrs.c -fschedule-insns
-fstrict-aliasing
Reading specs from
/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/lib/gcc/sparc-sun-solaris2.9/3.4.3/specs
Configured with: ./configure --prefix=/arm/eda/tools/gnu/gcc/3_4_3
--exec-prefix=/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc
--program-suffix=-3_4_3 --enable-languages=c,c++ -v --with-dwarf2
--enable-version-specific-runtime-libs --with-gnu-as
--with-as=/arm/eda/tools/gnu/binutils/2_15/solaris_2_9-sparc/bin/as-2_15
--with-gnu-ld
--with-ld=/arm/eda/tools/gnu/binutils/2_15/solaris_2_9-sparc/bin/ld-2_15
Thread model: posix
gcc version 3.4.3
/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/libexec/gcc/sparc-sun-solaris2.9/3.4.3/cc1plus
-E -quiet -v u64solrs.c -mcpu=v7 -fschedule-insns -fstrict-aliasing -O1 -o
u64solrs.ii
ignoring nonexistent directory
"/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/lib/gcc/sparc-sun-solaris2.9/3.4.3/../../../../sparc-sun-solaris2.9/include"
#include "..." search starts here:
#include <...> search starts here:
/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/lib/gcc/sparc-sun-solaris2.9/3.4.3/include/c++
/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/lib/gcc/sparc-sun-solaris2.9/3.4.3/include/c++/sparc-sun-solaris2.9
/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/lib/gcc/sparc-sun-solaris2.9/3.4.3/include/c++/backward
/usr/local/include
/arm/eda/tools/gnu/gcc/3_4_3/include
/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/lib/gcc/sparc-sun-solaris2.9/3.4.3/include
/usr/include
End of search list.
/arm/eda/tools/gnu/gcc/3_4_3/solaris_2_9-sparc/libexec/gcc/sparc-sun-solaris2.9/3.4.3/cc1plus
-fpreprocessed u64solrs.ii -quiet -dumpbase u64solrs.c -mcpu=v7 -auxbase-strip
u64solrs.o -O1 -version -fschedule-insns -fstrict-aliasing -o u64solrs.s
GNU C++ version 3.4.3 (sparc-sun-solaris2.9)
compiled by GNU C version 3.4.3.
GGC heuristics: --param ggc-min-expand=65 --param ggc-min-heapsize=65536
/arm/eda/tools/gnu/binutils/2_15/solaris_2_9-sparc/bin/as-2_15 -V -Qy -s
-xarch=v8 -o u64solrs.o u64solrs.s
GNU assembler version 2.15 (sparc-sun-solaris2.9) using BFD version 2.15
--
Summary: -fstrict-aliasing causes incorrect scheduling on Sparc
Solaris
Product: gcc
Version: 3.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: Ganesh dot Sittampalam at arm dot com
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: sparc-sun-solaris2.9
GCC host triplet: sparc-sun-solaris2.9
GCC target triplet: sparc-sun-solaris2.9
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20607
