Mesa (master): i965/fs: Don't emit null MOVs in CSE.

[Matt Turner]

Module: Mesa
Branch: master
Commit: 219b43c612b2882e0bf82ac1a12ff073a42be6e1
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=219b43c612b2882e0bf82ac1a12ff073a42be6e1

Author: Matt Turner <mattst88 at gmail.com>
Date:   Tue Oct 22 15:40:08 2013 -0700

i965/fs: Don't emit null MOVs in CSE.

We'd like to CSE some instructions, like CMP, that often have null
destinations. Instead of replacing them with MOVs to null, just don't
emit the MOV.

Reviewed-by: Paul Berry <stereotype441 at gmail.com>

---

 src/mesa/drivers/dri/i965/brw_fs_cse.cpp |   42 +++++++++++++++++------------
 1 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
index 0afc5f6..3f59339 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_cse.cpp
@@ -150,7 +150,7 @@ fs_visitor::opt_cse_local(bblock_t *block, exec_list *aeb)
 	     * If we don't have a temporary already, make one.
 	     */
 	    bool no_existing_temp = entry->tmp.file == BAD_FILE;
-	    if (no_existing_temp) {
+	    if (no_existing_temp && !entry->generator->dst.is_null()) {
                int written = entry->generator->regs_written;
 
                fs_reg orig_dst = entry->generator->dst;
@@ -171,29 +171,37 @@ fs_visitor::opt_cse_local(bblock_t *block, exec_list *aeb)
 	    }
 
 	    /* dest <- temp */
-            int written = inst->regs_written;
-            assert(written == entry->generator->regs_written);
-            assert(inst->dst.type == entry->tmp.type);
-            fs_reg dst = inst->dst;
-            fs_reg tmp = entry->tmp;
-            fs_inst *copy = NULL;
-            for (int i = 0; i < written; i++) {
-               copy = MOV(dst, tmp);
-               copy->force_writemask_all = inst->force_writemask_all;
-               inst->insert_before(copy);
-
-               dst.reg_offset++;
-               tmp.reg_offset++;
+            if (!inst->dst.is_null()) {
+               int written = inst->regs_written;
+               assert(written == entry->generator->regs_written);
+               assert(inst->dst.type == entry->tmp.type);
+               fs_reg dst = inst->dst;
+               fs_reg tmp = entry->tmp;
+               fs_inst *copy = NULL;
+               for (int i = 0; i < written; i++) {
+                  copy = MOV(dst, tmp);
+                  copy->force_writemask_all = inst->force_writemask_all;
+                  inst->insert_before(copy);
+
+                  dst.reg_offset++;
+                  tmp.reg_offset++;
+               }
             }
+
+            /* Set our iterator so that next time through the loop inst->next
+             * will get the instruction in the basic block after the one we've
+             * removed.
+             */
+            fs_inst *prev = (fs_inst *)inst->prev;
+
             inst->remove();
 
 	    /* Appending an instruction may have changed our bblock end. */
 	    if (inst == block->end) {
-	       block->end = copy;
+	       block->end = prev;
 	    }
 
-	    /* Continue iteration with copy->next */
-	    inst = copy;
+            inst = prev;
 	 }
       }