http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53712
Bug #: 53712
Summary: SEGV in generated code for _mm_cmpistri with unaligned
operand when using -O0
Classification: Unclassified
Product: gcc
Version: 4.6.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: [email protected]
ReportedBy: [email protected]
Created attachment 27647
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27647
Test program triggering the bug - compile with "-O0 -msse4.2"
Compile the attached program with "-msse4.2 -O0"
The failing generated code looks like this (-S):
test:
.LFB575:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
movq %rdi, -40(%rbp)
movq %rsi, -48(%rbp)
movq -48(%rbp), %rax
movq %rax, -24(%rbp)
movq -24(%rbp), %rax
movdqu (%rax), %xmm0
movdqa %xmm0, -16(%rbp)
movq -40(%rbp), %rax
SEGV => movdqa (%rax), %xmm1
movdqa -16(%rbp), %xmm0
pcmpistri $0, %xmm1, %xmm0
movl %ecx, %eax
? => pcmpistrm $0, %xmm1, %xmm0
popq %rbp
.cfi_def_cfa 7, 8
ret
.cfi_endproc
This code causes a SEGV at the indicated instruction, because %rax has a value
of 0x4006d8 which is not aligned by 16
Compiling with -O1 (or higher) fixes the problem:
test:
.LFB643:
.cfi_startproc
movdqu (%rsi), %xmm0
pcmpistri $0, (%rdi), %xmm0
movl %ecx, %eax
ret
.cfi_endproc
The root cause is that "pcmpistri" allows an unaligned memory operand, while
gcc generates aligned loads for the operands when using -O0.
A second issue is that gcc generates a redundant "pcmpistrm" instruction at
-O0, unclear where this is coming from?
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.6.3/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i686
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.6.3 20120306 (Red Hat 4.6.3-2) (GCC)
