[Bug rtl-optimization/15529] New: Use of regparm inhibits tail call optimization

["cesarb at nitnet dot com dot br" <gcc-bugzilla at gcc dot gnu dot org>]

(I would have put this in the right optimization component if I knew which of
them applies. Worse, bugzilla requires it. Let me take a guess... 50/50
chance... RTL?)

This is bug 14909 plus regparm. The testcase of bug 14909 works as expected.

When compiling:
//void g(void (*f)(void)) { f(); }
#define regparm __attribute__((regparm(3)))
void regparm g(void (regparm *f)()) { f(); }

With:
gcc -W -Wall -O3 -ffast-math -fomit-frame-pointer -fexpensive-optimizations
-save-temps -march=athlon -c
(most switches probably a red herring, didn't reduce the command line)

The result is:
	.file	"testcase.c"
	.text
	.align 4
	.p2align 4,,15
.globl g
	.type	g, @function
g:
	subl	$12, %esp
	call	*%eax
	addl	$12, %esp
	ret
	.size	g, .-g
	.ident	"GCC: (GNU) 3.5.0 20040502 (experimental)"
	.section	.note.GNU-stack,"",@progbits

It should be:
g:
	jmp *%eax

The use of regparm is superfluous in  this case, but the bug happens also in the
slightly less reduced testcase:

#define regparm __attribute__((regparm(3)))
void regparm g(void (regparm *f)(unsigned)) { f(0); }

Output:
	.file	"testcase2.c"
	.text
	.align 4
	.p2align 4,,15
.globl g
	.type	g, @function
g:
	subl	$12, %esp
	movl	%eax, %edx
	xorl	%eax, %eax
	call	*%edx
	addl	$12, %esp
	ret
	.size	g, .-g
	.ident	"GCC: (GNU) 3.5.0 20040502 (experimental)"
	.section	.note.GNU-stack,"",@progbits

The same happens when returning other than void (original testcase used
unsigned) -- same as bug 14909 in fact.

Reading specs from /usr/lib/gcc-snapshot/lib/gcc/i486-linux/3.5.0/specs
Configured with: ../src/configure -v
--enable-languages=c,c++,java,f77,objc,ada,treelang
--prefix=/usr/lib/gcc-snapshot --enable-shared --with-system-zlib --enable-nls
--enable-threads=posix --without-included-gettext --disable-werror
--enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug
--enable-java-gc=boehm --enable-java-awt=gtk i486-linux
Thread model: posix
gcc version 3.5.0 20040502 (experimental)

-- 
           Summary: Use of regparm inhibits tail call optimization
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: cesarb at nitnet dot com dot br
                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=15529