[Mesa-dev] [PATCH 2/3] i965/fs: Consider cmod when propagating to inst with different type.

[Matt Turner]

We can safely propagate the conditional mod to an instruction with a
different type if the conditional mod does not involve comparing for
equality with zero (or probably NaN, but ignore that for now).

This is because -0.0 and +0.0 are both test equal to zero, but their
integer representations do not.

Cc: 10.5 <mesa-stable at lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89317
---
 .../drivers/dri/i965/brw_fs_cmod_propagation.cpp   |  8 +++
 .../drivers/dri/i965/test_fs_cmod_propagation.cpp  | 67 ++++++++++++++++++++++
 2 files changed, 75 insertions(+)

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 c6384ab..a92eef6 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_cmod_propagation.cpp
@@ -80,6 +80,14 @@ opt_cmod_propagation_local(fs_visitor *v, bblock_t *block)
                 scan_inst->dst.reg_offset != inst->src[0].reg_offset)
                break;
 
+            /* Testing equality with zero is different for ints and floats */
+            if (scan_inst->dst.type != inst->dst.type &&
+                (inst->conditional_mod == BRW_CONDITIONAL_Z ||
+                 inst->conditional_mod == BRW_CONDITIONAL_NZ ||
+                 inst->conditional_mod == BRW_CONDITIONAL_GE ||
+                 inst->conditional_mod == BRW_CONDITIONAL_LE))
+               break;
+
             /* If the instruction generating inst's source also wrote the
              * flag, and inst is doing a simple .nz comparison, then inst
              * is redundant - the appropriate value is already in the flag
diff --git a/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp b/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp
index fbe4fd9..0287161 100644
--- a/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/test_fs_cmod_propagation.cpp
@@ -415,3 +415,70 @@ TEST_F(cmod_propagation_test, movnz)
    EXPECT_EQ(BRW_OPCODE_CMP, instruction(block0, 0)->opcode);
    EXPECT_EQ(BRW_CONDITIONAL_GE, instruction(block0, 0)->conditional_mod);
 }
+
+TEST_F(cmod_propagation_test, different_types)
+{
+   fs_reg dest = v->vgrf(glsl_type::int_type);
+   fs_reg src0 = v->vgrf(glsl_type::int_type);
+   fs_reg src1 = v->vgrf(glsl_type::int_type);
+   fs_reg zero(0.0f);
+   v->emit(BRW_OPCODE_ADD, dest, src0, src1);
+   v->emit(BRW_OPCODE_CMP, v->reg_null_f, retype(dest, BRW_REGISTER_TYPE_F),
+                                          zero)
+      ->conditional_mod = BRW_CONDITIONAL_G;
+
+   /* = Before =
+    *
+    * 0: add(8)        dest:D  src0:D  src1:D
+    * 1: cmp.g.f0(8)   null:F  dest:F  0.0f
+    *
+    * = After =
+    * 0: add.g.f0(8)   dest:D  src0:D  src1:D
+    */
+
+   v->calculate_cfg();
+   bblock_t *block0 = v->cfg->blocks[0];
+
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(1, block0->end_ip);
+
+   EXPECT_TRUE(cmod_propagation(v));
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(0, block0->end_ip);
+   EXPECT_EQ(BRW_OPCODE_ADD, instruction(block0, 0)->opcode);
+   EXPECT_EQ(BRW_CONDITIONAL_G, instruction(block0, 0)->conditional_mod);
+}
+
+TEST_F(cmod_propagation_test, different_types_cmod_with_zero)
+{
+   fs_reg dest = v->vgrf(glsl_type::int_type);
+   fs_reg src0 = v->vgrf(glsl_type::int_type);
+   fs_reg src1 = v->vgrf(glsl_type::int_type);
+   fs_reg zero(0.0f);
+   v->emit(BRW_OPCODE_ADD, dest, src0, src1);
+   v->emit(BRW_OPCODE_CMP, v->reg_null_f, retype(dest, BRW_REGISTER_TYPE_F),
+                                          zero)
+      ->conditional_mod = BRW_CONDITIONAL_GE;
+
+   /* = Before =
+    *
+    * 0: add(8)        dest:D  src0:D  src1:D
+    * 1: cmp.ge.f0(8)  null:F  dest:F  0.0f
+    *
+    * = After =
+    * (no changes)
+    */
+
+   v->calculate_cfg();
+   bblock_t *block0 = v->cfg->blocks[0];
+
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(1, block0->end_ip);
+
+   EXPECT_FALSE(cmod_propagation(v));
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(1, block0->end_ip);
+   EXPECT_EQ(BRW_OPCODE_ADD, instruction(block0, 0)->opcode);
+   EXPECT_EQ(BRW_OPCODE_CMP, instruction(block0, 1)->opcode);
+   EXPECT_EQ(BRW_CONDITIONAL_GE, instruction(block0, 1)->conditional_mod);
+}
-- 
2.0.5