[Mesa-dev] [PATCH] i965/vec4: fix record clearing in copy propagation

[Chia-I Wu]

From: Chia-I Wu <olv at lunarg.com>

Given

  mov vgrf7, vgrf9.xyxz
  add vgrf9.xyz, vgrf4.xyzw, vgrf5.xyzw
  add vgrf10.x, vgrf6.xyzw, vgrf7.wwww

the last instruction would be wrongly changed to

  add vgrf10.x, vgrf6.xyzw, vgrf9.zzzz

during copy propagation.

The issue is that when deciding if a record should be cleared, the old code
checked for

  inst->dst.writemask & (1 << ch)

instead of

  inst->dst.writemask & (1 << BRW_GET_SWZ(src->swizzle, ch))

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76749
Signed-off-by: Chia-I Wu <olv at lunarg.com>
Cc: Jordan Justen <jljusten at gmail.com>
Cc: Matt Turner <mattst88 at gmail.com>
---
 .../drivers/dri/i965/brw_vec4_copy_propagation.cpp  | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
index 3d68f0e..83cf191 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
@@ -58,6 +58,21 @@ is_dominated_by_previous_instruction(vec4_instruction *inst)
 }
 
 static bool
+is_channel_updated(vec4_instruction *inst, src_reg *values[4], int ch)
+{
+   const src_reg *src = values[ch];
+
+   /* consider GRF only */
+   assert(inst->dst.file == GRF);
+   if (!src || src->file != GRF)
+      return false;
+
+   return (src->reg == inst->dst.reg &&
+	   src->reg_offset == inst->dst.reg_offset &&
+	   inst->dst.writemask & (1 << BRW_GET_SWZ(src->swizzle, ch)));
+}
+
+static bool
 try_constant_propagation(vec4_instruction *inst, int arg, src_reg *values[4])
 {
    /* For constant propagation, we only handle the same constant
@@ -357,11 +372,7 @@ vec4_visitor::opt_copy_propagation()
 	 else {
 	    for (int i = 0; i < virtual_grf_reg_count; i++) {
 	       for (int j = 0; j < 4; j++) {
-		  if (inst->dst.writemask & (1 << j) &&
-		      cur_value[i][j] &&
-		      cur_value[i][j]->file == GRF &&
-		      cur_value[i][j]->reg == inst->dst.reg &&
-		      cur_value[i][j]->reg_offset == inst->dst.reg_offset) {
+		  if (is_channel_updated(inst, cur_value[i], j)){
 		     cur_value[i][j] = NULL;
 		  }
 	       }
-- 
1.8.5.3