[Mesa-dev] [PATCH] i965: Fix constant propagation into 32-bit integer MUL.

[Paul Berry]

i965's MUL instruction can't take an immediate value as its first
argument.  So normally, if constant propagation wants to propagate a
constant into the first argument of a MUL instruction, it swaps the
order of the two arguments.

This doesn't work for 32-bit integer (and unsigned integer)
multiplies, because the MUL operation is asymmetric in that case (it
multiplies 16 bits of one operand by 32 bits of the other).

Fixes piglit tests {vs,fs}-multiply-const-{ivec4,uvec4}.
---
 src/mesa/drivers/dri/i965/brw_fs.cpp               |    9 ++++++++-
 .../drivers/dri/i965/brw_vec4_copy_propagation.cpp |    8 +++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index e58545b..b66febb 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -1127,7 +1127,14 @@ fs_visitor::propagate_constants()
 		  scan_inst->src[i] = inst->src[0];
 		  progress = true;
 	       } else if (i == 0 && scan_inst->src[1].file != IMM) {
-		  /* Fit this constant in by commuting the operands */
+		  /* Fit this constant in by commuting the operands.
+		   * Exception: we can't do this for 32-bit integer MUL
+		   * because it's asymmetric.
+		   */
+		  if (scan_inst->opcode == BRW_OPCODE_MUL &&
+		      (scan_inst->src[1].type == BRW_REGISTER_TYPE_D ||
+		       scan_inst->src[1].type == BRW_REGISTER_TYPE_UD))
+		     break;
 		  scan_inst->src[0] = scan_inst->src[1];
 		  scan_inst->src[1] = inst->src[0];
 		  progress = true;
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 c3a9dee..93ae3d6 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_copy_propagation.cpp
@@ -101,7 +101,13 @@ try_constant_propagation(vec4_instruction *inst, int arg, src_reg *values[4])
 	 inst->src[arg] = value;
 	 return true;
       } else if (arg == 0 && inst->src[1].file != IMM) {
-	 /* Fit this constant in by commuting the operands */
+	 /* Fit this constant in by commuting the operands.  Exception: we
+	  * can't do this for 32-bit integer MUL because it's asymmetric.
+	  */
+	 if (inst->opcode == BRW_OPCODE_MUL &&
+	     (inst->src[1].type == BRW_REGISTER_TYPE_D ||
+	      inst->src[1].type == BRW_REGISTER_TYPE_UD))
+	    break;
 	 inst->src[0] = inst->src[1];
 	 inst->src[1] = value;
 	 return true;
-- 
1.7.6.4