i965/fs: Use the gen7 scratch read opcode when possible.

This avoids a lot of message setup we had to do otherwise.  Improves
GLB2.7 performance with register spilling force enabled by 1.6442% +/-
0.553218% (n=4).

v2: Use BRW_PREDICATE_NONE, improve a comment (by Paul).

Reviewed-by: Paul Berry <stereotype441@gmail.com>

8 files changed, 91 insertions, 3 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_defines.h b/src/mesa/drivers/dri/i965/brw_defines.h
index 2248693..bad6d40 100644
--- a/src/mesa/drivers/dri/i965/brw_defines.h
+++ b/src/mesa/drivers/dri/i965/brw_defines.h
@@ -780,6 +780,7 @@ enum opcode {
 
    SHADER_OPCODE_GEN4_SCRATCH_READ,
    SHADER_OPCODE_GEN4_SCRATCH_WRITE,
+   SHADER_OPCODE_GEN7_SCRATCH_READ,
 
    FS_OPCODE_DDX,
    FS_OPCODE_DDY,
@@ -1141,6 +1142,12 @@ enum brw_message_target {
 #define GEN7_DATAPORT_DC_BYTE_SCATTERED_WRITE                       12
 #define GEN7_DATAPORT_DC_UNTYPED_SURFACE_WRITE                      13
 
+#define GEN7_DATAPORT_SCRATCH_READ                            ((1 << 18) | \
+                                                               (0 << 17))
+#define GEN7_DATAPORT_SCRATCH_WRITE                           ((1 << 18) | \
+                                                               (1 << 17))
+#define GEN7_DATAPORT_SCRATCH_NUM_REGS_SHIFT                        12
+
 /* HSW */
 #define HSW_DATAPORT_DC_PORT0_OWORD_BLOCK_READ                      0
 #define HSW_DATAPORT_DC_PORT0_UNALIGNED_OWORD_BLOCK_READ            1
diff --git a/src/mesa/drivers/dri/i965/brw_eu.h b/src/mesa/drivers/dri/i965/brw_eu.h
index 1a448d0..01f8bcc 100644
--- a/src/mesa/drivers/dri/i965/brw_eu.h
+++ b/src/mesa/drivers/dri/i965/brw_eu.h
@@ -379,6 +379,11 @@ void brw_oword_block_write_scratch(struct brw_compile *p,
 				   int num_regs,
 				   GLuint offset);
 
+void gen7_block_read_scratch(struct brw_compile *p,
+                             struct brw_reg dest,
+                             int num_regs,
+                             GLuint offset);
+
 void brw_shader_time_add(struct brw_compile *p,
                          struct brw_reg payload,
                          uint32_t surf_index);
diff --git a/src/mesa/drivers/dri/i965/brw_eu_emit.c b/src/mesa/drivers/dri/i965/brw_eu_emit.c
index 34239be..cc093e0 100644
--- a/src/mesa/drivers/dri/i965/brw_eu_emit.c
+++ b/src/mesa/drivers/dri/i965/brw_eu_emit.c
@@ -2055,6 +2055,48 @@ brw_oword_block_read_scratch(struct brw_compile *p,
    }
 }
 
+void
+gen7_block_read_scratch(struct brw_compile *p,
+                        struct brw_reg dest,
+                        int num_regs,
+                        GLuint offset)
+{
+   dest = retype(dest, BRW_REGISTER_TYPE_UW);
+
+   struct brw_instruction *insn = next_insn(p, BRW_OPCODE_SEND);
+
+   assert(insn->header.predicate_control == BRW_PREDICATE_NONE);
+   insn->header.compression_control = BRW_COMPRESSION_NONE;
+
+   brw_set_dest(p, insn, dest);
+
+   /* The HW requires that the header is present; this is to get the g0.5
+    * scratch offset.
+    */
+   bool header_present = true;
+   brw_set_src0(p, insn, brw_vec8_grf(0, 0));
+
+   brw_set_message_descriptor(p, insn,
+                              GEN7_SFID_DATAPORT_DATA_CACHE,
+                              1, /* mlen: just g0 */
+                              num_regs,
+                              header_present,
+                              false);
+
+   insn->bits3.ud |= GEN7_DATAPORT_SCRATCH_READ;
+
+   assert(num_regs == 1 || num_regs == 2 || num_regs == 4);
+   insn->bits3.ud |= (num_regs - 1) << GEN7_DATAPORT_SCRATCH_NUM_REGS_SHIFT;
+
+   /* According to the docs, offset is "A 12-bit HWord offset into the memory
+    * Immediate Memory buffer as specified by binding table 0xFF."  An HWORD
+    * is 32 bytes, which happens to be the size of a register.
+    */
+   offset /= REG_SIZE;
+   assert(offset < (1 << 12));
+   insn->bits3.ud |= offset;
+}
+
 /**
  * Read a float[4] vector from the data port Data Cache (const buffer).
  * Location (in buffer) should be a multiple of 16.
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 0512ab4..a3a4dc0 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -525,6 +525,7 @@ private:
                      bool negate_value);
    void generate_scratch_write(fs_inst *inst, struct brw_reg src);
    void generate_scratch_read(fs_inst *inst, struct brw_reg dst);
+   void generate_scratch_read_gen7(fs_inst *inst, struct brw_reg dst);
    void generate_uniform_pull_constant_load(fs_inst *inst, struct brw_reg dst,
                                             struct brw_reg index,
                                             struct brw_reg offset);
diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
index 2172949..672e896 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
@@ -770,6 +770,12 @@ fs_generator::generate_scratch_read(fs_inst *inst, struct brw_reg dst)
 }
 
 void
+fs_generator::generate_scratch_read_gen7(fs_inst *inst, struct brw_reg dst)
+{
+   gen7_block_read_scratch(p, dst, dispatch_width / 8, inst->offset);
+}
+
+void
 fs_generator::generate_uniform_pull_constant_load(fs_inst *inst,
                                                   struct brw_reg dst,
                                                   struct brw_reg index,
@@ -1587,6 +1593,10 @@ fs_generator::generate_code(exec_list *instructions)
 	 generate_scratch_read(inst, dst);
 	 break;
 
+      case SHADER_OPCODE_GEN7_SCRATCH_READ:
+	 generate_scratch_read_gen7(inst, dst);
+	 break;
+
       case FS_OPCODE_UNIFORM_PULL_CONSTANT_LOAD:
 	 generate_uniform_pull_constant_load(inst, dst, src[0], src[1]);
 	 break;
diff --git a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
index d975423..d9e80d0 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
@@ -542,14 +542,22 @@ fs_visitor::emit_unspill(fs_inst *inst, fs_reg dst, uint32_t spill_offset,
                          int count)
 {
    for (int i = 0; i < count; i++) {
+      /* The gen7 descriptor-based offset is 12 bits of HWORD units. */
+      bool gen7_read = brw->gen >= 7 && spill_offset < (1 << 12) * REG_SIZE;
+
       fs_inst *unspill_inst =
-         new(mem_ctx) fs_inst(SHADER_OPCODE_GEN4_SCRATCH_READ, dst);
+         new(mem_ctx) fs_inst(gen7_read ?
+                              SHADER_OPCODE_GEN7_SCRATCH_READ :
+                              SHADER_OPCODE_GEN4_SCRATCH_READ,
+                              dst);
       unspill_inst->offset = spill_offset;
       unspill_inst->ir = inst->ir;
       unspill_inst->annotation = inst->annotation;
 
-      unspill_inst->base_mrf = 14;
-      unspill_inst->mlen = 1; /* header contains offset */
+      if (!gen7_read) {
+         unspill_inst->base_mrf = 14;
+         unspill_inst->mlen = 1; /* header contains offset */
+      }
       inst->insert_before(unspill_inst);
 
       dst.reg_offset++;
@@ -617,6 +625,7 @@ fs_visitor::choose_spill_reg(struct ra_graph *g)
 	 break;
 
       case SHADER_OPCODE_GEN4_SCRATCH_READ:
+      case SHADER_OPCODE_GEN7_SCRATCH_READ:
 	 if (inst->dst.file == GRF)
 	    no_spill[inst->dst.reg] = true;
 	 break;
diff --git a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
index 5093dd5..9e4de29 100644
--- a/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
+++ b/src/mesa/drivers/dri/i965/brw_schedule_instructions.cpp
@@ -342,6 +342,18 @@ schedule_node::set_latency_gen7(bool is_haswell)
       latency = 200;
       break;
 
+   case SHADER_OPCODE_GEN7_SCRATCH_READ:
+      /* Testing a load from offset 0, that had been previously written:
+       *
+       * send(8) g114<1>UW g0<8,8,1>F data (0, 0, 0) mlen 1 rlen 1 { align1 WE_normal 1Q };
+       * mov(8)  null      g114<8,8,1>F { align1 WE_normal 1Q };
+       *
+       * The cycles spent seemed to be grouped around 40-50 (as low as 38),
+       * then around 140.  Presumably this is cache hit vs miss.
+       */
+      latency = 50;
+      break;
+
    default:
       /* 2 cycles:
        * mul(8) g4<1>F g2<0,1,0>F      0.5F            { align1 WE_normal 1Q };
diff --git a/src/mesa/drivers/dri/i965/brw_shader.cpp b/src/mesa/drivers/dri/i965/brw_shader.cpp
index a351183..b7b0a5b 100644
--- a/src/mesa/drivers/dri/i965/brw_shader.cpp
+++ b/src/mesa/drivers/dri/i965/brw_shader.cpp
@@ -458,6 +458,8 @@ brw_instruction_name(enum opcode op)
       return "gen4_scratch_read";
    case SHADER_OPCODE_GEN4_SCRATCH_WRITE:
       return "gen4_scratch_write";
+   case SHADER_OPCODE_GEN7_SCRATCH_READ:
+      return "gen7_scratch_read";
 
    case FS_OPCODE_DDX:
       return "ddx";