[Mesa-dev] [PATCH] intel/compiler: fix node interference of simd16 instructions

[Iago Toral Quiroga]

SIMD16 instructions need to have additional interferences to prevent
source / destination hazards when the source and destination registers
are off by one register.

While we already have code to handle this, it was only running for SIMD16
dispatches, however, we can have SIDM16 instructions in a SIMD8 dispatch.
An example of this are pull constant loads since commit b56fa830c6095,
but there are more cases.

This fixes a number of CTS test failues found in work-in-progress
tests that were hitting this situation for 16-wide pull constants
in a SIMD8 program.
---
 src/intel/compiler/brw_fs_reg_allocate.cpp | 36 ++++++++++------------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/src/intel/compiler/brw_fs_reg_allocate.cpp b/src/intel/compiler/brw_fs_reg_allocate.cpp
index 42ccb28de6..f72826bc41 100644
--- a/src/intel/compiler/brw_fs_reg_allocate.cpp
+++ b/src/intel/compiler/brw_fs_reg_allocate.cpp
@@ -632,26 +632,24 @@ fs_visitor::assign_regs(bool allow_spilling, bool spill_all)
       }
    }
 
-   if (dispatch_width > 8) {
-      /* In 16-wide dispatch we have an issue where a compressed
-       * instruction is actually two instructions executed simultaneiously.
-       * It's actually ok to have the source and destination registers be
-       * the same.  In this case, each instruction over-writes its own
-       * source and there's no problem.  The real problem here is if the
-       * source and destination registers are off by one.  Then you can end
-       * up in a scenario where the first instruction over-writes the
-       * source of the second instruction.  Since the compiler doesn't know
-       * about this level of granularity, we simply make the source and
-       * destination interfere.
-       */
-      foreach_block_and_inst(block, fs_inst, inst, cfg) {
-         if (inst->dst.file != VGRF)
-            continue;
+   /* In 16-wide instructions we have an issue where a compressed
+    * instruction is actually two instructions executed simultaneiously.
+    * It's actually ok to have the source and destination registers be
+    * the same.  In this case, each instruction over-writes its own
+    * source and there's no problem.  The real problem here is if the
+    * source and destination registers are off by one.  Then you can end
+    * up in a scenario where the first instruction over-writes the
+    * source of the second instruction.  Since the compiler doesn't know
+    * about this level of granularity, we simply make the source and
+    * destination interfere.
+    */
+   foreach_block_and_inst(block, fs_inst, inst, cfg) {
+      if (inst->exec_size < 16 || inst->dst.file != VGRF)
+         continue;
 
-         for (int i = 0; i < inst->sources; ++i) {
-            if (inst->src[i].file == VGRF) {
-               ra_add_node_interference(g, inst->dst.nr, inst->src[i].nr);
-            }
+      for (int i = 0; i < inst->sources; ++i) {
+         if (inst->src[i].file == VGRF) {
+            ra_add_node_interference(g, inst->dst.nr, inst->src[i].nr);
          }
       }
    }
-- 
2.17.1