tree cc733cd757d7f826295bf04e8d1772b4ec5605ef
parent 909d7f9bf5168621efc4c8daf8c61b1936a66fe9
author qining <qining@google.com> 1471468788 -0400
committer qining <qining@google.com> 1472744765 -0400

Unify constants pass

De-duplicate constants and unifies the uses of constants for a SPIR-V
module. If two constants are defined exactly the same, only one of them
will be kept and all the uses of the removed constant will be redirected
to the kept one.

This pass handles normal constants (defined with
OpConstant{|True|False|Composite}), some spec constants (those defined
with OpSpecConstant{Op|Composite}) and null constants (defined with
OpConstantNull).

There are several cases not handled by this pass:

  1) If there are decorations for the result id of a constant defining
  instruction, that instruction will not be processed. This means the
  instruction won't be used to replace other instructions and other
  instructions won't be used to replace it either.

  2) This pass does not unify null constants (defined with
  OpConstantNull instruction) with their equivalent zero-valued normal
  constants (defined with OpConstant{|False|Composite} with zero as the
  operand values or component values).