[Mesa-dev] [PATCH 2/3] glsl: Skip rewriting instructions in opt_cpe when unnecessary.

[Kenneth Graunke]

Previously, opt_copy_propagation_elements would always rewrite the
instruction stream, even if was the same thing as before.  In order to
report progress correctly, we'll need to bail if the suggested
replacement is identical (or equivalent) to the original code.

This also introduced unnecessary noop swizzles, as far as I can tell.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/glsl/opt_copy_propagation_elements.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/glsl/opt_copy_propagation_elements.cpp b/src/glsl/opt_copy_propagation_elements.cpp
index f131894..a67f507 100644
--- a/src/glsl/opt_copy_propagation_elements.cpp
+++ b/src/glsl/opt_copy_propagation_elements.cpp
@@ -209,6 +209,7 @@ ir_copy_propagation_elements_visitor::handle_rvalue(ir_rvalue **ir)
    ir_variable *source[4] = {NULL, NULL, NULL, NULL};
    int source_chan[4] = {0, 0, 0, 0};
    int chans;
+   bool noop_swizzle = true;
 
    if (!*ir)
       return;
@@ -250,6 +251,9 @@ ir_copy_propagation_elements_visitor::handle_rvalue(ir_rvalue **ir)
 	    if (entry->write_mask & (1 << swizzle_chan[c])) {
 	       source[c] = entry->rhs;
 	       source_chan[c] = entry->swizzle[swizzle_chan[c]];
+
+               if (source_chan[c] != swizzle_chan[c])
+                  noop_swizzle = false;
 	    }
 	 }
       }
@@ -266,6 +270,12 @@ ir_copy_propagation_elements_visitor::handle_rvalue(ir_rvalue **ir)
    if (!shader_mem_ctx)
       shader_mem_ctx = ralloc_parent(deref_var);
 
+   /* Don't pointlessly replace the rvalue with itself (or a noop swizzle
+    * of itself, which would just be deleted by opt_noop_swizzle).
+    */
+   if (source[0] == var && noop_swizzle)
+      return;
+
    if (debug) {
       printf("Copy propagation from:\n");
       (*ir)->print();
-- 
2.1.0