i965/vec4: track and use independently each flag channel

vec4_live_variables tracks now each flag channel independently, so
vec4_dead_code_eliminate can update the writemask of null registers,
based on which component are alive at the moment. This would allow
vec4_cmod_propagation to optimize out several movs involving null
registers.

v2: added support to track each flag channel independently at vec4
    live_variables, as v1 assumed that it was already doing it, as
    pointed by Francisco Jerez
v3: general cleaningn after Matt Turner's review

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

1 files changed, 21 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_ir_vec4.h b/src/mesa/drivers/dri/i965/brw_ir_vec4.h
index 1b57b65db27..74e9733bd44 100644
--- a/src/mesa/drivers/dri/i965/brw_ir_vec4.h
+++ b/src/mesa/drivers/dri/i965/brw_ir_vec4.h
@@ -186,6 +186,27 @@ public:
       return predicate || opcode == VS_OPCODE_UNPACK_FLAGS_SIMD4X2;
    }
 
+   bool reads_flag(unsigned c)
+   {
+      if (!reads_flag())
+         return false;
+
+      switch (predicate) {
+      case BRW_PREDICATE_NONE:
+         return false;
+      case BRW_PREDICATE_ALIGN16_REPLICATE_X:
+         return c == 0;
+      case BRW_PREDICATE_ALIGN16_REPLICATE_Y:
+         return c == 1;
+      case BRW_PREDICATE_ALIGN16_REPLICATE_Z:
+         return c == 2;
+      case BRW_PREDICATE_ALIGN16_REPLICATE_W:
+         return c == 3;
+      default:
+         return true;
+      }
+   }
+
    bool writes_flag()
    {
       return (conditional_mod && (opcode != BRW_OPCODE_SEL &&