Mesa (master): vc4: Put dead writes into the NOP register when generating code.

[Eric Anholt]

Module: Mesa
Branch: master
Commit: 9dbfca10a306fe5ae5b81845cb8f4d16022d6790
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=9dbfca10a306fe5ae5b81845cb8f4d16022d6790

Author: Eric Anholt <eric at anholt.net>
Date:   Tue Sep 23 13:20:29 2014 -0700

vc4: Put dead writes into the NOP register when generating code.

They still provide register pressure since I haven't made a special class
for them, but since they're only live for one instruction it probably
doesn't matter.

This improves the readability of QPU assembly.

---

 src/gallium/drivers/vc4/vc4_register_allocate.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/gallium/drivers/vc4/vc4_register_allocate.c b/src/gallium/drivers/vc4/vc4_register_allocate.c
index 639037e..72f5271 100644
--- a/src/gallium/drivers/vc4/vc4_register_allocate.c
+++ b/src/gallium/drivers/vc4/vc4_register_allocate.c
@@ -237,9 +237,16 @@ vc4_register_allocate(struct vc4_context *vc4, struct vc4_compile *c)
         bool ok = ra_allocate(g);
         assert(ok);
 
-        for (uint32_t i = 0; i < c->num_temps; i++)
+        for (uint32_t i = 0; i < c->num_temps; i++) {
                 temp_registers[i] = vc4_regs[ra_get_node_reg(g, i)];
 
+                /* If the value's never used, just write to the NOP register
+                 * for clarity in debug output.
+                 */
+                if (def[i] == use[i])
+                        temp_registers[i] = qpu_ra(QPU_W_NOP);
+        }
+
         ralloc_free(g);
 
         return temp_registers;