i965/fs: fix lower SIMD width for IVB/BYT's MOV_INDIRECT

According to the IVB and HSW PRMs:

"2.When the destination requires two registers and the sources are
 indirect, the sources must use 1x1 regioning mode."

So for DF instructions the execution size is not limited by the number
of address registers that are available, but by the EU decompression
logic not handling VxH indirect addressing correctly.

This patch limits the SIMD width to 4 in this case.

v2:
- Fix typo (Matt).
- Fix condition (Curro)

v3:
- Add spec quote (Curro)

Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>

1 files changed, 14 insertions, 3 deletions

diff --git a/src/intel/compiler/brw_fs.cpp b/src/intel/compiler/brw_fs.cpp
index f96e0a3989..cae15542fa 100644
--- a/src/intel/compiler/brw_fs.cpp
+++ b/src/intel/compiler/brw_fs.cpp
@@ -4891,11 +4891,22 @@ get_lowered_simd_width(const struct gen_device_info *devinfo,
    case SHADER_OPCODE_URB_WRITE_SIMD8_MASKED_PER_SLOT:
       return MIN2(8, inst->exec_size);
 
-   case SHADER_OPCODE_MOV_INDIRECT:
-      /* Prior to Broadwell, we only have 8 address subregisters */
+   case SHADER_OPCODE_MOV_INDIRECT: {
+      /* From IVB and HSW PRMs:
+       *
+       * "2.When the destination requires two registers and the sources are
+       *  indirect, the sources must use 1x1 regioning mode.
+       *
+       * In case of DF instructions in HSW/IVB, the exec_size is limited by
+       * the EU decompression logic not handling VxH indirect addressing
+       * correctly.
+       */
+      const unsigned max_size = (devinfo->gen >= 8 ? 2 : 1) * REG_SIZE;
+      /* Prior to Broadwell, we only have 8 address subregisters. */
       return MIN3(devinfo->gen >= 8 ? 16 : 8,
-                  2 * REG_SIZE / (inst->dst.stride * type_sz(inst->dst.type)),
+                  max_size / (inst->dst.stride * type_sz(inst->dst.type)),
                   inst->exec_size);
+   }
 
    case SHADER_OPCODE_LOAD_PAYLOAD: {
       const unsigned reg_count =