[Mesa-dev] [PATCH 13/15] i965/fs: Add support for MOV_INDIRECT on pre-Broadwell hardware

[Jason Ekstrand]

While we're at it, we also add support for the possibility that the
indirect is, in fact, a constant.  This shouldn't happen in the common case
(if it does, that means NIR failed to constant-fold something), but it's
possible so we should handle it.
---
 src/mesa/drivers/dri/i965/brw_fs.cpp           |  4 ++
 src/mesa/drivers/dri/i965/brw_fs_generator.cpp | 51 +++++++++++++++++++-------
 2 files changed, 42 insertions(+), 13 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 9eaf8d0..a2ec03e 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -4424,6 +4424,10 @@ get_lowered_simd_width(const struct brw_device_info *devinfo,
    case SHADER_OPCODE_TYPED_SURFACE_WRITE_LOGICAL:
       return 8;
 
+   case SHADER_OPCODE_MOV_INDIRECT:
+      /* Prior to Broadwell, we only have 8 address subregisters */
+      return devinfo->gen < 8 ? 8 : inst->exec_size;
+
    default:
       return inst->exec_size;
    }
diff --git a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
index d86eee1..7fa6d84 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_generator.cpp
@@ -351,22 +351,47 @@ fs_generator::generate_mov_indirect(fs_inst *inst,
 
    unsigned imm_byte_offset = reg.nr * REG_SIZE + reg.subnr;
 
-   /* We use VxH indirect addressing, clobbering a0.0 through a0.7. */
-   struct brw_reg addr = vec8(brw_address_reg(0));
+   if (indirect_byte_offset.file == BRW_IMMEDIATE_VALUE) {
+      imm_byte_offset += indirect_byte_offset.ud;
 
-   /* The destination stride of an instruction (in bytes) must be greater
-    * than or equal to the size of the rest of the instruction.  Since the
-    * address register is of type UW, we can't use a D-type instruction.
-    * In order to get around this, re re-type to UW and use a stride.
-    */
-   indirect_byte_offset =
-      retype(spread(indirect_byte_offset, 2), BRW_REGISTER_TYPE_UW);
+      reg.nr = imm_byte_offset / REG_SIZE;
+      reg.subnr = imm_byte_offset % REG_SIZE;
+      brw_MOV(p, dst, reg);
+   } else {
+      /* Prior to Broadwell, there are only 8 address registers. */
+      assert(inst->exec_size == 8 || devinfo->gen >= 8);
 
-   /* Prior to Broadwell, there are only 8 address registers. */
-   assert(inst->exec_size == 8 || devinfo->gen >= 8);
+      /* We use VxH indirect addressing, clobbering a0.0 through a0.7. */
+      struct brw_reg addr = vec8(brw_address_reg(0));
 
-   brw_MOV(p, addr, indirect_byte_offset);
-   brw_MOV(p, dst, retype(brw_VxH_indirect(0, imm_byte_offset), dst.type));
+      /* The destination stride of an instruction (in bytes) must be greater
+       * than or equal to the size of the rest of the instruction.  Since the
+       * address register is of type UW, we can't use a D-type instruction.
+       * In order to get around this, re re-type to UW and use a stride.
+       */
+      indirect_byte_offset =
+         retype(spread(indirect_byte_offset, 2), BRW_REGISTER_TYPE_UW);
+
+      if (devinfo->gen < 8) {
+         /* Prior to broadwell, we have a restriction that the bottom 5 bits
+          * of the base offset and the bottom 5 bits of the indirect must add
+          * to less than 32.  In other words, the hardware needs to be able to
+          * add the bottom five bits of the two to get the subnumber and add
+          * the next 7 bits of each to get the actual register number.  Since
+          * the indirect may cause us to cross a register boundary, this makes
+          * it almost useless.  We could try and do something clever where we
+          * use a actual base offset if base_offset % 32 == 0 but that would
+          * mean we were generating different code depending on the base
+          * offset.  Instead, for the sake of consistency, we'll just do the
+          * add ourselves.
+          */
+         brw_ADD(p, addr, indirect_byte_offset, brw_imm_uw(imm_byte_offset));
+         brw_MOV(p, dst, retype(brw_VxH_indirect(0, 0), dst.type));
+      } else {
+         brw_MOV(p, addr, indirect_byte_offset);
+         brw_MOV(p, dst, retype(brw_VxH_indirect(0, imm_byte_offset), dst.type));
+      }
+   }
 }
 
 void
-- 
2.5.0.400.gff86faf