[Mesa-dev] [PATCH v4 17/44] i965/fs: Add remove_extra_rounding_modes optimization

[Jose Maria Casanova Crespo]

From: Alejandro Piñeiro <apinheiro at igalia.com>

Although from SPIR-V point of view, rounding modes are attached to the
operation/destination, on i965 it is a status, so we don't need to
explicitly set the rounding mode if the one we want is already set.

Taking into account that the default mode is RTE, one possible
optimization would be optimize out the first RTE set for each
block. For in order to work, we would need to take into account block
interrelationships. At this point, it is not worth to complicate the
optimization for such small gain.

v2: Use a single SHADER_OPCODE_RND_MODE opcode taking an immediate
    with the rounding mode (Curro)
v3: Reset optimization for every block. (Jason Ekstrand)

Signed-off-by: Jose Maria Casanova Crespo <jmcasanova at igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro at igalia.com>
Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
---
 src/intel/compiler/brw_eu_defines.h |  1 +
 src/intel/compiler/brw_fs.cpp       | 37 +++++++++++++++++++++++++++++++++++++
 src/intel/compiler/brw_fs.h         |  1 +
 3 files changed, 39 insertions(+)

diff --git a/src/intel/compiler/brw_eu_defines.h b/src/intel/compiler/brw_eu_defines.h
index 8a8f36cbc1..9d5cf05c86 100644
--- a/src/intel/compiler/brw_eu_defines.h
+++ b/src/intel/compiler/brw_eu_defines.h
@@ -1252,6 +1252,7 @@ enum PACKED brw_rnd_mode {
    BRW_RND_MODE_RU = 1,    /* Round Up, toward +inf */
    BRW_RND_MODE_RD = 2,    /* Round Down, toward -inf */
    BRW_RND_MODE_RTZ = 3,   /* Round Toward Zero */
+   BRW_RND_MODE_UNSPECIFIED,  /* Unspecified rounding mode */
 };
 
 #endif /* BRW_EU_DEFINES_H */
diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index 6cdd2bd9f3..36fb337c62 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -3092,6 +3092,42 @@ fs_visitor::remove_duplicate_mrf_writes()
    return progress;
 }
 
+/**
+ * Rounding modes for conversion instructions are included for each
+ * conversion, but right now it is a state. So once it is set,
+ * we don't need to call it again for subsequent calls.
+ *
+ * This is useful for vector/matrices conversions, as setting the
+ * mode once is enough for the full vector/matrix
+ */
+bool
+fs_visitor::remove_extra_rounding_modes()
+{
+   bool progress = false;
+
+   foreach_block (block, cfg) {
+      brw_rnd_mode prev_mode = BRW_RND_MODE_UNSPECIFIED;
+
+      foreach_inst_in_block_safe (fs_inst, inst, block) {
+         if (inst->opcode == SHADER_OPCODE_RND_MODE) {
+            assert(inst->src[0].file == BRW_IMMEDIATE_VALUE);
+            const brw_rnd_mode mode = (brw_rnd_mode) inst->src[0].d;
+            if (mode == prev_mode) {
+               inst->remove(block);
+               progress = true;
+            } else {
+               prev_mode = mode;
+            }
+         }
+      }
+   }
+
+   if (progress)
+      invalidate_live_intervals();
+
+   return progress;
+}
+
 static void
 clear_deps_for_inst_src(fs_inst *inst, bool *deps, int first_grf, int grf_len)
 {
@@ -5808,6 +5844,7 @@ fs_visitor::optimize()
    int pass_num = 0;
 
    OPT(opt_drop_redundant_mov_to_flags);
+   OPT(remove_extra_rounding_modes);
 
    do {
       progress = false;
diff --git a/src/intel/compiler/brw_fs.h b/src/intel/compiler/brw_fs.h
index 40dd83f45e..19b897e7a9 100644
--- a/src/intel/compiler/brw_fs.h
+++ b/src/intel/compiler/brw_fs.h
@@ -150,6 +150,7 @@ public:
    bool eliminate_find_live_channel();
    bool dead_code_eliminate();
    bool remove_duplicate_mrf_writes();
+   bool remove_extra_rounding_modes();
 
    bool opt_sampler_eot();
    bool virtual_grf_interferes(int a, int b);
-- 
2.14.3