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nir/deref: Drop zero ptr_as_array derefs

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They are effectively (&x)[0] or *&x which does nothing.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
This commit is contained in:
Jason Ekstrand 2019-02-03 09:32:32 -06:00
parent aaef12702f
commit 36734987a5
1 changed files with 21 additions and 0 deletions
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21
src/compiler/nir/nir_deref.c
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@ -670,6 +670,27 @@ opt_deref_ptr_as_array(nir_builder *b, nir_deref_instr *deref)
assert(deref->deref_type == nir_deref_type_ptr_as_array);
nir_deref_instr *parent = nir_deref_instr_parent(deref);
if (nir_src_is_const(deref->arr.index) &&
nir_src_as_int(deref->arr.index) == 0) {
/* If it's a ptr_as_array deref with an index of 0, it does nothing
* and we can just replace its uses with its parent.
*
* The source of a ptr_as_array deref always has a deref_type of
* nir_deref_type_array or nir_deref_type_cast. If it's a cast, it
* may be trivial and we may be able to get rid of that too. Any
* trivial cast of trivial cast cases should be handled already by
* opt_deref_cast() above.
*/
if (parent->deref_type == nir_deref_type_cast &&
is_trivial_deref_cast(parent))
parent = nir_deref_instr_parent(parent);
nir_ssa_def_rewrite_uses(&deref->dest.ssa,
nir_src_for_ssa(&parent->dest.ssa));
nir_instr_remove(&deref->instr);
return true;
}
if (parent->deref_type != nir_deref_type_array &&
parent->deref_type != nir_deref_type_ptr_as_array)
return false;