[PATCH] Handle GIMPLE_ASSIGNs with different vuse in gimple_equal_p

[Tom de Vries]

Richard,

Consider the test-case test.c:
...
int z;
int x;

void
f (int c, int d)
{
   if (c)
     z = 5;
   else
     {
       if (d)
	x = 4;
       z = 5;
     }
}
...

Atm, we don't tail-merge the 'z = 5' blocks, because gimple_equal_p returns 
false for the 'z = 5' statements. The relevant code is this:
...
       if (TREE_CODE (lhs1) != SSA_NAME
           && TREE_CODE (lhs2) != SSA_NAME)
         return (vn_valueize (gimple_vdef (s1))
                 == vn_valueize (gimple_vdef (s2)));
...
The vdefs of the 'z = 5' statements are different, because the incoming vuses 
are different.

This patch handles GIMPLE_ASSIGNs with different vuse in gimple_equal_p, by 
doing a structural comparison.

Bootstrapped and regtested on x86_64.

OK for trunk?

Thanks,
- Tom

2013-11-06  Tom de Vries  <tom@codesourcery.com>

	* tree-ssa-tail-merge.c (gimple_equal_p): Add test for structural
	equality for GIMPLE_ASSIGN.

	* gcc.dg/tail-merge-store.c: New test.
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