[Bug c/60754] New: Missed optimization with inline asm longer than 3 lines

[Bug c/60754] New: Missed optimization with inline asm longer than 3 lines

[rabin at rab dot in]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60754

            Bug ID: 60754
           Summary: Missed optimization with inline asm longer than 3
                    lines
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rabin at rab dot in

Created attachment 32538
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32538&action=edit
Testcase

At -O2 GCC does not optimize out the call to fail() in the following program if
the asm has four lines.

$ cat testcase.c
extern void fail(void) __attribute__((error("fail")));

static void function(int magic)
{
     if (magic > 1)
         fail();

    __asm__(
    "// comment\n"            
    "// comment\n"            
    "// comment\n"            
#ifndef THREELINEASM
    "// comment\n"            
#endif
    ::);
}

void another(void)
{
    function(0);
    function(1);
}

void dummy(void)
{
    another();
}
$ gcc -c -O2 testcase.c
testcase.c: In function ‘function’:
testcase.c:6:8: error: call to ‘fail’ declared with attribute error: fail
    fail();
        ^
$ gcc -c -O2 -DTHREELINEASM  testcase.c
$ gcc -c -Os testcase.c
$ gcc -c -O3 testcase.c
$ gcc -v
Using built-in specs.
COLLECT_GCC=/usr/bin/gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.8.2-16'
--with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.8 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap
--enable-plugin --with-system-zlib --disable-browser-plugin
--enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --with-arch-32=i586 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.2 (Debian 4.8.2-16)
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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/60754] Missed optimization with inline asm longer than 3 lines
Date: Thu, 03 Apr 2014 23:26:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id`754

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is about inlining differences.  In the THREELINEASM case, the function
gets inlined, in the non case, it is not.  This is just a heuristic of the cost
model.