[Bug c/21970] New: Inline keyword causes computation to erroneously reduce to a constant

["para at cfl dot rr dot com" <gcc-bugzilla at gcc dot gnu dot org>]

I have a function which evaluates the SHA-1 cryptographic hash function. It 
takes as parameters the 160-bit state and 64 bytes to hash and produces an 
output 160-bit state. When compiling at -O0, it is horrendously slow, but it 
(as far as I know) produces correct behavior. For quick reference, a (brief) 
function definition follows:


typedef unsigned long UINT32;

typedef struct
{
	UINT32 a, b, c, d, e;
} SHA1_STATE;

void sha1(SHA1_STATE *pState, void const *pvBuf);


At -O1 and above, the SHA-1 function is reduced to the following code:


_sha1:
	pushl	%ebp
	movl	%esp, %ebp
	movl	8(%ebp), %eax
	movl	$0, (%eax)
	movl	$0, 4(%eax)
	movl	$0, 8(%eax)
	movl	$0, 12(%eax)
	movl	$0, 16(%eax)
	popl	%ebp
	ret


Because this file is autogenerated, I generate function calls to do trivial 
operations such as addition and rely on function inlining to preserve 
performance. If these functions are not marked with the inline keyword, then 
this bug does not trigger. Also, I tried removing roughly half of the code from 
the function, and it cause the bug to no longer trigger. I removed all code 
below line 316 and simply copied the final 5 keys from the key schedule (w75, 
w76, w77, w78, w79) to the output state.

I have observed the same behavior on MinGW GCC versions 3.3.1 and 3.4.2. The 
output of gcc -v for the version I am reporting against is as follows:

Reading specs from /usr/lib/gcc/i686-pc-linux-gnu/3.4.4/specs
Configured with: /var/tmp/portage/gcc-3.4.4/work/gcc-3.4.4/configure --enable-
version-specific-runtime-libs --prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-
bin/3.4.4 --includedir=/usr/lib/gcc/i686-pc-linux-gnu/3.4.4/include --
datadir=/usr/share/gcc-data/i686-pc-linux-gnu/3.4.4 --mandir=/usr/share/gcc-
data/i686-pc-linux-gnu/3.4.4/man --infodir=/usr/share/gcc-data/i686-pc-linux-
gnu/3.4.4/info --with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-
gnu/3.4.4/include/g++-v3 --host=i686-pc-linux-gnu --disable-altivec --enable-
nls --without-included-gettext --with-system-zlib --disable-checking --disable-
werror --disable-libunwind-exceptions --disable-multilib --disable-libgcj --
enable-languages=c,c++ --enable-shared --enable-threads=posix --enable-
__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 3.4.4 (Gentoo Hardened 3.4.4, ssp-3.4.4-1.0, pie-8.7.8)

-- 
           Summary: Inline keyword causes computation to erroneously reduce
                    to a constant
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: para at cfl dot rr dot com
                CC: gcc-bugs at gcc dot gnu dot org
 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=21970