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Re: combine permutations in gimple


On Mon, 13 Aug 2012, Richard Guenther wrote:

+  /* Check that it is only used here. We cannot use has_single_use
+     since the expression is using it twice itself...  */

Ah ... so then


|| num_imm_uses (op0) != 2

Ah, ok, that's simpler indeed, but there were such dire warnings to never use that evil function unless absolutely necessary that I didn't dare use it... Thanks for the permission.

If your new predicate would match more places (can you do a quick search?)

You mean: if there are more optimizations that either already check for double use in the same statement, or could benefit from doing so? I'll take a look.


then we want it in tree-flow-inline.h instead of in
tree-ssa-forwprop.c.  But yes,
num_imm_uses can be expensive.   For now just stick with the above.

I assume "the above" means "num_imm_uses (op0) != 2", since both versions are above ;-)


The natural SSA (and forwprop) way is to look for BIT_FIELD_REF and see
if the def stmt is a VEC_PERM_EXPR.

Thanks again,


--
Marc Glisse


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