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From: Miles Bader <miles@gnu.org>
To: Jeff Law <law@redhat.com>
Cc: Jeff Kenton <jkenton@tilera.com>, Ian Lance Taylor <iant@google.com>, David Brown <david@westcontrol.com>, Georg-Johann Lay <avr@gjlay.de>, gcc-help@gcc.gnu.org, charfiasma@yahoo.fr
Subject: Re: Tr : [redundency elimination, code motion, commun  expression elimination] GCC optimizations
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Jeff Law <law@redhat.com> writes:
> The tail merging code in the RTL optimizers might pick this stuff up
> and Tom's work on block merging might as well.  It'd be worth
> looking into why they aren't triggering.

Hmm, actually testing with a recent gcc snapshot, it _is_ merging the
two if-blocks:

   int a, b, c, d, e, f;
   extern void foo ();
   void t (int x)
   {
     if (x==1) { a=b; c=d; e=f; foo(); }
     if (x==2) { a=b; c=d; e=f; foo(); }
   }

=>

   t:
           cmpl	$1, %edi
           je	.L4
           cmpl	$2, %edi
           je	.L4
           rep
           ret
   .L4:
           movl	b(%rip), %eax
           movl	%eax, a(%rip)
           movl	d(%rip), %eax
           movl	%eax, c(%rip)
           movl	f(%rip), %eax
           movl	%eax, e(%rip)
           xorl	%eax, %eax
           jmp	foo
           ...
           .ident	"GCC: (Debian 20110924-1) 4.7.0 20110924 (experimental) [trunk revision 179143]"

-Miles

-- 
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