glsl: Rework assignments with write_masks to have LHS chan count match RHS.

It turns out that most people new to this IR are surprised when an
assignment to (say) 3 components on the LHS takes 4 components on the
RHS.  It also makes for quite strange IR output:

(assign (constant bool (1)) (x) (var_ref color) (swiz x (var_ref v) ))
(assign (constant bool (1)) (y) (var_ref color) (swiz yy (var_ref v) ))
(assign (constant bool (1)) (z) (var_ref color) (swiz zzz (var_ref v) ))

But even worse, even we get it wrong, as shown by this line of our
current step(float, vec4):

(assign (constant bool (1)) (w)
	(var_ref t)
	(expression float b2f (expression bool >=
		    (swiz w (var_ref x))(var_ref edge))))

where we try to assign a float to the writemasked-out x channel and
don't supply anything for the actual w channel we're writing.  Drivers
right now just get lucky since ir_to_mesa spams the float value across
all the source channels of a vec4.

Instead, the RHS will now have a number of components equal to the
number of components actually being written.  Hopefully this confuses
everyone less, and it also makes codegen for a scalar target simpler.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

1 files changed, 9 insertions, 7 deletions

diff --git a/src/glsl/ir_validate.cpp b/src/glsl/ir_validate.cpp
index 912d1c0d709..e35514aa6f9 100644
--- a/src/glsl/ir_validate.cpp
+++ b/src/glsl/ir_validate.cpp
@@ -391,14 +391,16 @@ ir_validate::visit_enter(ir_assignment *ir)
 	 abort();
       }
 
-      /* Mask of fields that do not exist in the destination.  These should
-       * not be written by the assignment.
-       */
-      const unsigned invalid_mask = ~((1U << lhs->type->components()) - 1);
+      int lhs_components = 0;
+      for (int i = 0; i < 4; i++) {
+	 if (ir->write_mask & (1 << i))
+	    lhs_components++;
+      }
 
-      if ((invalid_mask & ir->write_mask) != 0) {
-	 printf("Assignment write mask enables invalid components for "
-		"type %s:\n", lhs->type->name);
+      if (lhs_components != ir->rhs->type->vector_elements) {
+	 printf("Assignment count of LHS write mask channels enabled not\n"
+		"matching RHS vector size (%d LHS, %d RHS).\n",
+		lhs_components, ir->rhs->type->vector_elements);
 	 ir->print();
 	 abort();
       }