glsl: Skip rewriting instructions in opt_cpe when unnecessary.

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 <[email protected]>
Reviewed-by: Matt Turner <[email protected]>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/glsl/opt_copy_propagation_elements.cpp b/src/glsl/opt_copy_propagation_elements.cpp
index f131894608d..a67f5070cb0 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();