nir/algebraic: Optimize integer cast-of-cast

These have been popping up more and more with the OpenCL work and other
bits causing extra conversions to/from 64-bit.

Reviewed-by: Karol Herbst <kherbst@redhat.com>

src/compiler/nir/nir_opt_algebraic.py

@@ -884,6 +884,48 @@ for x, y in itertools.product(['f', 'u', 'i'], ['f', 'u', 'i']):
    x2yN = '{}2{}'.format(x, y)
    optimizations.append(((x2yN, (b2x, a)), (b2y, a)))
 
+# Optimize away x2xN(a@N)
+for t in ['int', 'uint', 'float']:
+   for N in type_sizes(t):
+      x2xN = '{0}2{0}{1}'.format(t[0], N)
+      aN = 'a@{0}'.format(N)
+      optimizations.append(((x2xN, aN), a))
+
+# Optimize x2xN(y2yM(a@P)) -> y2yN(a) for integers
+# In particular, we can optimize away everything except upcast of downcast and
+# upcasts where the type differs from the other cast
+for N, M in itertools.product(type_sizes('uint'), type_sizes('uint')):
+   if N < M:
+      # The outer cast is a down-cast.  It doesn't matter what the size of the
+      # argument of the inner cast is because we'll never been in the upcast
+      # of downcast case.  Regardless of types, we'll always end up with y2yN
+      # in the end.
+      for x, y in itertools.product(['i', 'u'], ['i', 'u']):
+         x2xN = '{0}2{0}{1}'.format(x, N)
+         y2yM = '{0}2{0}{1}'.format(y, M)
+         y2yN = '{0}2{0}{1}'.format(y, N)
+         optimizations.append(((x2xN, (y2yM, a)), (y2yN, a)))
+   elif N > M:
+      # If the outer cast is an up-cast, we have to be more careful about the
+      # size of the argument of the inner cast and with types.  In this case,
+      # the type is always the type of type up-cast which is given by the
+      # outer cast.
+      for P in type_sizes('uint'):
+         # We can't optimize away up-cast of down-cast.
+         if M < P:
+            continue
+
+         # Because we're doing down-cast of down-cast, the types always have
+         # to match between the two casts
+         for x in ['i', 'u']:
+            x2xN = '{0}2{0}{1}'.format(x, N)
+            x2xM = '{0}2{0}{1}'.format(x, M)
+            aP = 'a@{0}'.format(P)
+            optimizations.append(((x2xN, (x2xM, aP)), (x2xN, a)))
+   else:
+      # The N == M case is handled by other optimizations
+      pass
+
 def fexp2i(exp, bits):
    # We assume that exp is already in the right range.
    if bits == 16: