When I compile the attached source file, the s2_multiway_merge function gets
apparently miscompiled. The do loop near the end of this function loses both of
its terminating conditions and it is compiled to:
.L101:
addl $1, %esi
.L53:
movl -76(%ebp), %edi
movl -92(%ebp), %eax
movl -96(%ebp), %edx
movl -32(%ebp), %ecx
movl -36(%ebp), %ebx
movl %edi, -4(%eax,%esi,4)
movl -52(%ebp), %eax
movl -100(%ebp), %edi
movl %ecx, -4(%edx,%esi,4)
movl -40(%ebp), %edx
movl %eax, -4(%edi,%esi,4)
movl $-1, (%edx)
.L88:
shrl %ebx
je .L101
[... the s2_update_tree loop got inlined here, this test is its correct
terminating condition ...]
It seems that gcc thinks that `i' never changes in the loop, so it has
optimized out every expression which depends in its value.
I apologize for submitting a large source file, but the problem appears to be
very chaotic and even removing parts of the source which are not referenced
anywhere (see for example the block with the MAGIC comment attached) makes the
problem disappear.
Compilation command: gcc-4.2.1 -v -std=gnu99 -O2 -S xxx.c -Wunused
-fgnu89-inline
Output:
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ./configure --prefix=/opt/gcc-4.2.1 --enable-bootstrap
Thread model: posix
gcc version 4.2.1
/opt/gcc-4.2.1/libexec/gcc/i686-pc-linux-gnu/4.2.1/cc1 -quiet -v xxx.c -quiet
-dumpbase xxx.c -mtune=generic -auxbase xxx -O2 -Wunused -std=gnu99 -version
-fgnu89-inline -o xxx.s
ignoring nonexistent directory
"/opt/gcc-4.2.1/lib/gcc/i686-pc-linux-gnu/4.2.1/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/opt/gcc-4.2.1/include
/opt/gcc-4.2.1/lib/gcc/i686-pc-linux-gnu/4.2.1/include
/usr/include
End of search list.
GNU C version 4.2.1 (i686-pc-linux-gnu)
compiled by GNU C version 4.2.1.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 9831b30df15d36dc669e016cd6c4ba43
--
Summary: Disappearing loop conditions
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: mj at ucw dot cz
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33262
