Mesa (master): glsl: Fix copy_propagation_elements bug in handling self-copies.

[Eric Anholt]

Module: Mesa
Branch: master
Commit: 057f9ae54b5efb0020cc0c049d50e778de3f3f7a
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=057f9ae54b5efb0020cc0c049d50e778de3f3f7a

Author: Eric Anholt <eric at anholt.net>
Date:   Mon Jan  9 13:30:55 2012 -0800

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 at whitecape.org>

---

 src/glsl/opt_copy_propagation_elements.cpp |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/src/glsl/opt_copy_propagation_elements.cpp b/src/glsl/opt_copy_propagation_elements.cpp
index be446bc..ebfd4fd 100644
--- 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);
 }