[Mesa-dev] [PATCH 3/5] i965/fs: Handle CMP.nz ... 0 and AND.nz ... 1 similarly in cmod propagation

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

Espically on platforms that do not natively generate 0u and ~0u for
Boolean results, we generate a lot of sequences where a CMP is
followed by an AND with 1.  emit_bool_to_cond_code does this, for
example.  On ILK, this results in a sequence like:

    add(8)          g3<1>F          g8<8,8,1>F      -g4<0,1,0>F
    cmp.l.f0(8)     g3<1>D          g3<8,8,1>F      0F
    and.nz.f0(8)    null            g3<8,8,1>D      1D
    (+f0) iff(8)    Jump: 6

The AND.nz is obviously redundant.  By propagating the cmod, we can
instead generate

    add.l.f0(8)     null            g8<8,8,1>F      -g4<0,1,0>F
    (+f0) iff(8)    Jump: 6

Existing code already handles the propagation from the CMP to the ADD.

Shader-db results:

GM45 (0x2A42):
total instructions in shared programs: 3550829 -> 3550788 (-0.00%)
instructions in affected programs:     10028 -> 9987 (-0.41%)
helped:                                24

Iron Lake (0x0046):
total instructions in shared programs: 4993146 -> 4993105 (-0.00%)
instructions in affected programs:     9675 -> 9634 (-0.42%)
helped:                                24

Ivy Bridge (0x0166):
total instructions in shared programs: 6291870 -> 6291794 (-0.00%)
instructions in affected programs:     17914 -> 17838 (-0.42%)
helped:                                48

Haswell (0x0426):
total instructions in shared programs: 5779256 -> 5779180 (-0.00%)
instructions in affected programs:     16694 -> 16618 (-0.46%)
helped:                                48

Broadwell (0x162E):
total instructions in shared programs: 6823088 -> 6823014 (-0.00%)
instructions in affected programs:     15824 -> 15750 (-0.47%)
helped:                                46

No chage on Sandy Bridge or on any platform when NIR is used.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Cc: Matt Turner <mattst88 at gmail.com>
---
 .../drivers/dri/i965/brw_fs_cmod_propagation.cpp   | 32 +++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
index d0ca2f9..6df3d45 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
@@ -57,7 +57,8 @@ opt_cmod_propagation_local(bblock_t *block)
    foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
       ip--;
 
-      if ((inst->opcode != BRW_OPCODE_CMP &&
+      if ((inst->opcode != BRW_OPCODE_AND &&
+           inst->opcode != BRW_OPCODE_CMP &&
            inst->opcode != BRW_OPCODE_MOV) ||
           inst->predicate != BRW_PREDICATE_NONE ||
           !inst->dst.is_null() ||
@@ -65,6 +66,19 @@ opt_cmod_propagation_local(bblock_t *block)
           inst->src[0].abs)
          continue;
 
+      /* Only an AND.NZ can be propagated.  Many AND.Z instructions are
+       * generated (for ir_unop_not in fs_visitor::emit_bool_to_cond_code).
+       * Propagating those would require inverting the condition on the CMP.
+       * This changes both the flag value and the register destination of the
+       * CMP.  That result may be used elsewhere, so we can't change its value
+       * on a whim.
+       */
+      if (inst->opcode == BRW_OPCODE_AND &&
+          !(inst->src[1].is_one() &&
+            inst->conditional_mod == BRW_CONDITIONAL_NZ &&
+            !inst->src[0].negate))
+         continue;
+
       if (inst->opcode == BRW_OPCODE_CMP && !inst->src[1].is_zero())
          continue;
 
@@ -80,6 +94,22 @@ opt_cmod_propagation_local(bblock_t *block)
                 scan_inst->dst.reg_offset != inst->src[0].reg_offset)
                break;
 
+            /* This must be done before the dst.type check because the result
+             * type of the AND will always be D, but the result of the CMP
+             * could be anything.  The assumption is that the AND is just
+             * figuring out what the result of the previous comparison was
+             * instead of doing a new comparison with a different type.
+             */
+            if (inst->opcode == BRW_OPCODE_AND) {
+               if (scan_inst->opcode == BRW_OPCODE_CMP &&
+                   scan_inst->writes_flag()) {
+                  inst->remove(block);
+                  progress = true;
+               }
+
+               break;
+            }
+
             /* Comparisons operate differently for ints and floats */
             if (scan_inst->dst.type != inst->dst.type)
                break;
-- 
2.1.0