intel/fs: Fix flag_subreg handling in cmod propagation

There were two errors.  First, the pass could propagate conditional
modifiers from an instruction that writes on flag register to an
instruction that writes a different flag register.  For example,

    cmp.nz.f0.0(16) null:F, vgrf6:F, vgrf5:F
    cmp.nz.f0.1(16) null:F, vgrf6:F, vgrf5:F

could be come

    cmp.nz.f0.0(16) null:F, vgrf6:F, vgrf5:F

Second, if an instruction writes f0.1 has it's condition propagated, the
modified instruction will incorrectly write flag f0.0.  For example,

    linterp(16) vgrf6:F, g2:F, attr0:F
    cmp.z.f0.1(16) null:F, vgrf6:F, vgrf5:F
    (-f0.1) discard_jump(16) (null):UD

could become

    linterp.z.f0.0(16) vgrf6:F, g2:F, attr0:F
    (-f0.1) discard_jump(16) (null):UD

None of these cases will occur currently.  The only time we use f0.1 is
for generating discard intrinsics.  In all those cases, we generate a
squence like:

    cmp.nz.f0.0(16) vgrf7:F, vgrf6:F, vgrf5:F
    (+f0.1) cmp.z(16) null:D, vgrf7:D, 0d
    (-f0.1) discard_jump(16) (null):UD

Due to the mixed types and incompatible conditions, this sequence would
never see any cmod propagation.  The next patch will change this.

No shader-db changes on any Intel platform.

v2: Fix typo in comment in test case subtract_delete_compare_other_flag.
Noticed by Caio.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

2 files changed, 196 insertions, 0 deletions

diff --git a/src/intel/compiler/brw_fs_cmod_propagation.cpp b/src/intel/compiler/brw_fs_cmod_propagation.cpp
index b430d4b2446..ba4df592424 100644
--- a/src/intel/compiler/brw_fs_cmod_propagation.cpp
+++ b/src/intel/compiler/brw_fs_cmod_propagation.cpp
@@ -53,6 +53,7 @@ cmod_propagate_cmp_to_add(const gen_device_info *devinfo, bblock_t *block,
                           fs_inst *inst)
 {
    bool read_flag = false;
+   const unsigned flags_written = inst->flags_written();
 
    foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst) {
       if (scan_inst->opcode == BRW_OPCODE_ADD &&
@@ -79,6 +80,17 @@ cmod_propagate_cmp_to_add(const gen_device_info *devinfo, bblock_t *block,
             goto not_match;
          }
 
+         /* If the scan instruction writes a different flag register than the
+          * instruction we're trying to propagate from, bail.
+          *
+          * FINISHME: The second part of the condition may be too strong.
+          * Perhaps (scan_inst->flags_written() & flags_written) !=
+          * flags_written?
+          */
+         if (scan_inst->flags_written() != 0 &&
+             scan_inst->flags_written() != flags_written)
+            goto not_match;
+
          /* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
           *
           *    * Note that the [post condition signal] bits generated at
@@ -130,6 +142,7 @@ cmod_propagate_not(const gen_device_info *devinfo, bblock_t *block,
 {
    const enum brw_conditional_mod cond = brw_negate_cmod(inst->conditional_mod);
    bool read_flag = false;
+   const unsigned flags_written = inst->flags_written();
 
    if (cond != BRW_CONDITIONAL_Z && cond != BRW_CONDITIONAL_NZ)
       return false;
@@ -146,6 +159,17 @@ cmod_propagate_not(const gen_device_info *devinfo, bblock_t *block,
              scan_inst->exec_size != inst->exec_size)
             break;
 
+         /* If the scan instruction writes a different flag register than the
+          * instruction we're trying to propagate from, bail.
+          *
+          * FINISHME: The second part of the condition may be too strong.
+          * Perhaps (scan_inst->flags_written() & flags_written) !=
+          * flags_written?
+          */
+         if (scan_inst->flags_written() != 0 &&
+             scan_inst->flags_written() != flags_written)
+            break;
+
          if (scan_inst->can_do_cmod() &&
              ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
               scan_inst->conditional_mod == cond)) {
@@ -231,9 +255,21 @@ opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block)
       }
 
       bool read_flag = false;
+      const unsigned flags_written = inst->flags_written();
       foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst) {
          if (regions_overlap(scan_inst->dst, scan_inst->size_written,
                              inst->src[0], inst->size_read(0))) {
+            /* If the scan instruction writes a different flag register than
+             * the instruction we're trying to propagate from, bail.
+             *
+             * FINISHME: The second part of the condition may be too strong.
+             * Perhaps (scan_inst->flags_written() & flags_written) !=
+             * flags_written?
+             */
+            if (scan_inst->flags_written() != 0 &&
+                scan_inst->flags_written() != flags_written)
+               break;
+
             if (scan_inst->is_partial_write() ||
                 scan_inst->dst.offset != inst->src[0].offset ||
                 scan_inst->exec_size != inst->exec_size)
@@ -380,6 +416,7 @@ opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block)
                 ((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
                  scan_inst->conditional_mod == cond)) {
                scan_inst->conditional_mod = cond;
+               scan_inst->flag_subreg = inst->flag_subreg;
                inst->remove(block);
                progress = true;
             }
diff --git a/src/intel/compiler/test_fs_cmod_propagation.cpp b/src/intel/compiler/test_fs_cmod_propagation.cpp
index 3aa3459caf2..89e2684eafb 100644
--- a/src/intel/compiler/test_fs_cmod_propagation.cpp
+++ b/src/intel/compiler/test_fs_cmod_propagation.cpp
@@ -140,6 +140,40 @@ TEST_F(cmod_propagation_test, basic)
    EXPECT_EQ(BRW_CONDITIONAL_GE, instruction(block0, 0)->conditional_mod);
 }
 
+TEST_F(cmod_propagation_test, basic_other_flag)
+{
+   const fs_builder &bld = v->bld;
+   fs_reg dest = v->vgrf(glsl_type::float_type);
+   fs_reg src0 = v->vgrf(glsl_type::float_type);
+   fs_reg src1 = v->vgrf(glsl_type::float_type);
+   fs_reg zero(brw_imm_f(0.0f));
+   bld.ADD(dest, src0, src1);
+   bld.CMP(bld.null_reg_f(), dest, zero, BRW_CONDITIONAL_GE)
+      ->flag_subreg = 1;
+
+   /* = Before =
+    *
+    * 0: add(8)         dest  src0  src1
+    * 1: cmp.ge.f0.1(8) null  dest  0.0f
+    *
+    * = After =
+    * 0: add.ge.f0.1(8) dest  src0  src1
+    */
+
+   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(1, instruction(block0, 0)->flag_subreg);
+   EXPECT_EQ(BRW_CONDITIONAL_GE, instruction(block0, 0)->conditional_mod);
+}
+
 TEST_F(cmod_propagation_test, cmp_nonzero)
 {
    const fs_builder &bld = v->bld;
@@ -864,6 +898,84 @@ TEST_F(cmod_propagation_test, subtract_delete_compare)
    EXPECT_EQ(BRW_PREDICATE_NORMAL, instruction(block0, 1)->predicate);
 }
 
+TEST_F(cmod_propagation_test, subtract_delete_compare_other_flag)
+{
+   /* This test is the same as subtract_delete_compare but it explicitly used
+    * flag f0.1 for the subtraction and the comparison.
+    */
+   const fs_builder &bld = v->bld;
+   fs_reg dest = v->vgrf(glsl_type::float_type);
+   fs_reg dest1 = v->vgrf(glsl_type::float_type);
+   fs_reg src0 = v->vgrf(glsl_type::float_type);
+   fs_reg src1 = v->vgrf(glsl_type::float_type);
+   fs_reg src2 = v->vgrf(glsl_type::float_type);
+
+   set_condmod(BRW_CONDITIONAL_L, bld.ADD(dest, src0, negate(src1)))
+      ->flag_subreg = 1;
+   set_predicate(BRW_PREDICATE_NORMAL, bld.MOV(dest1, src2));
+   bld.CMP(bld.null_reg_f(), src0, src1, BRW_CONDITIONAL_L)
+      ->flag_subreg = 1;
+
+   /* = Before =
+    * 0: add.l.f0.1(8)   dest0:F src0:F  -src1:F
+    * 1: (+f0) mov(0)    dest1:F src2:F
+    * 2: cmp.l.f0.1(8)   null:F  src0:F  src1:F
+    *
+    * = After =
+    * 0: add.l.f0.1(8)   dest:F  src0:F  -src1:F
+    * 1: (+f0) mov(0)    dest1:F src2:F
+    */
+   v->calculate_cfg();
+   bblock_t *block0 = v->cfg->blocks[0];
+
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(2, block0->end_ip);
+
+   EXPECT_TRUE(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_CONDITIONAL_L, instruction(block0, 0)->conditional_mod);
+   EXPECT_EQ(1, instruction(block0, 0)->flag_subreg);
+   EXPECT_EQ(BRW_OPCODE_MOV, instruction(block0, 1)->opcode);
+   EXPECT_EQ(BRW_PREDICATE_NORMAL, instruction(block0, 1)->predicate);
+}
+
+TEST_F(cmod_propagation_test, subtract_to_mismatch_flag)
+{
+   const fs_builder &bld = v->bld;
+   fs_reg dest = v->vgrf(glsl_type::float_type);
+   fs_reg src0 = v->vgrf(glsl_type::float_type);
+   fs_reg src1 = v->vgrf(glsl_type::float_type);
+
+   set_condmod(BRW_CONDITIONAL_L, bld.ADD(dest, src0, negate(src1)));
+   bld.CMP(bld.null_reg_f(), src0, src1, BRW_CONDITIONAL_L)
+      ->flag_subreg = 1;
+
+   /* = Before =
+    * 0: add.l.f0(8)     dest0:F src0:F  -src1:F
+    * 1: cmp.l.f0.1(8)   null:F  src0:F  src1:F
+    *
+    * = 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_CONDITIONAL_L, instruction(block0, 0)->conditional_mod);
+   EXPECT_EQ(0, instruction(block0, 0)->flag_subreg);
+   EXPECT_EQ(BRW_OPCODE_CMP, instruction(block0, 1)->opcode);
+   EXPECT_EQ(BRW_CONDITIONAL_L, instruction(block0, 1)->conditional_mod);
+   EXPECT_EQ(1, instruction(block0, 1)->flag_subreg);
+}
+
 TEST_F(cmod_propagation_test, subtract_delete_compare_derp)
 {
    const fs_builder &bld = v->bld;
@@ -1643,6 +1755,53 @@ TEST_F(cmod_propagation_test, not_to_or_intervening_flag_read_compatible_value)
    EXPECT_EQ(BRW_PREDICATE_NORMAL, instruction(block0, 1)->predicate);
 }
 
+TEST_F(cmod_propagation_test,
+       not_to_or_intervening_flag_read_compatible_value_mismatch_flag)
+{
+   /* Exercise propagation of conditional modifier from a NOT instruction to
+    * another ALU instruction as performed by cmod_propagate_not.
+    */
+   const fs_builder &bld = v->bld;
+   fs_reg dest0 = v->vgrf(glsl_type::uint_type);
+   fs_reg dest1 = v->vgrf(glsl_type::float_type);
+   fs_reg src0 = v->vgrf(glsl_type::uint_type);
+   fs_reg src1 = v->vgrf(glsl_type::uint_type);
+   fs_reg src2 = v->vgrf(glsl_type::float_type);
+   fs_reg zero(brw_imm_f(0.0f));
+   set_condmod(BRW_CONDITIONAL_Z, bld.OR(dest0, src0, src1))
+      ->flag_subreg = 1;
+   set_predicate(BRW_PREDICATE_NORMAL, bld.SEL(dest1, src2, zero));
+   set_condmod(BRW_CONDITIONAL_NZ, bld.NOT(bld.null_reg_ud(), dest0));
+
+   /* = Before =
+    *
+    * 0: or.z.f0.1(8)  dest0 src0  src1
+    * 1: (+f0) sel(8)  dest1 src2  0.0f
+    * 2: not.nz.f0(8)  null  dest0
+    *
+    * = After =
+    * No changes
+    */
+
+   v->calculate_cfg();
+   bblock_t *block0 = v->cfg->blocks[0];
+
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(2, block0->end_ip);
+
+   EXPECT_FALSE(cmod_propagation(v));
+   EXPECT_EQ(0, block0->start_ip);
+   EXPECT_EQ(2, block0->end_ip);
+   EXPECT_EQ(BRW_OPCODE_OR, instruction(block0, 0)->opcode);
+   EXPECT_EQ(BRW_CONDITIONAL_Z, instruction(block0, 0)->conditional_mod);
+   EXPECT_EQ(1, instruction(block0, 0)->flag_subreg);
+   EXPECT_EQ(BRW_OPCODE_SEL, instruction(block0, 1)->opcode);
+   EXPECT_EQ(BRW_PREDICATE_NORMAL, instruction(block0, 1)->predicate);
+   EXPECT_EQ(BRW_OPCODE_NOT, instruction(block0, 2)->opcode);
+   EXPECT_EQ(BRW_CONDITIONAL_NZ, instruction(block0, 2)->conditional_mod);
+   EXPECT_EQ(0, instruction(block0, 2)->flag_subreg);
+}
+
 TEST_F(cmod_propagation_test, not_to_or_intervening_flag_read_incompatible_value)
 {
    /* Exercise propagation of conditional modifier from a NOT instruction to