glsl: Fix copy_propagation_elements bug in handling self-copies.

We were doing the kill of the updated channels, then adding our copy
to the list of available stuff to copy.  But if the copy was updating
its own source channels, we didn't notice, breaking this code:

	R0.xyzw = arg0 + arg1;
	R0.xyzw = R0.wwwx;
	gl_FragColor.xyzw = clamp(R0.xyzw, 0.0, 1.0);

Fixes piglit glsl-copy-propagation-self-2.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

diff --git a/src/glsl/opt_copy_propagation_elements.cpp b/src/glsl/opt_copy_propagation_elements.cpp
index be446bc08ba9947620796eb1e33ac3cef606ba96..ebfd4fd3fe1365758ac6243c7945d62b32365f93 100644 (file)
--- a/src/glsl/opt_copy_propagation_elements.cpp
+++ b/src/glsl/opt_copy_propagation_elements.cpp
@@ -461,7 +461,20 @@ ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
         swizzle[i] = orig_swizzle[j++];
    }
 
-   entry = new(this->mem_ctx) acp_entry(lhs->var, rhs->var, ir->write_mask,
+   int write_mask = ir->write_mask;
+   if (lhs->var == rhs->var) {
+      /* If this is a copy from the variable to itself, then we need
+       * to be sure not to include the updated channels from this
+       * instruction in the set of new source channels to be
+       * copy-propagated from.
+       */
+      for (int i = 0; i < 4; i++) {
+        if (ir->write_mask & (1 << orig_swizzle[i]))
+           write_mask &= ~(1 << i);
+      }
+   }
+
+   entry = new(this->mem_ctx) acp_entry(lhs->var, rhs->var, write_mask,
                                        swizzle);
    this->acp->push_tail(entry);
 }