r300/compiler: Fix incorrect presubtract conversion

ADD instructions with constant swizzles can't be converted to
presubtract operations.

NOTE: This is a candidate for the 7.9 and 7.10 branches.

diff --git a/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c b/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c
index c4e6a5e0a1fc2743b4325b77f2874d7c40eb9dd6..79898e1047eabff254eae71421d27e4ab8692ba2 100644 (file)
--- a/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c
+++ b/src/mesa/drivers/dri/r300/compiler/radeon_optimize.c
@@ -509,10 +509,34 @@ static int is_presub_candidate(
 {
        const struct rc_opcode_info * info = rc_get_opcode_info(inst->U.I.Opcode);
        unsigned int i;
+       unsigned int is_constant[2] = {0, 0};
+
+       assert(inst->U.I.Opcode == RC_OPCODE_ADD);
 
        if (inst->U.I.PreSub.Opcode != RC_PRESUB_NONE || inst->U.I.SaturateMode)
                return 0;
 
+       /* If both sources use a constant swizzle, then we can't convert it to
+        * a presubtract operation.  In fact for the ADD and SUB presubtract
+        * operations neither source can contain a constant swizzle.  This
+        * specific case is checked in peephole_add_presub_add() when
+        * we make sure the swizzles for both sources are equal, so we
+        * don't need to worry about it here. */
+       for (i = 0; i < 2; i++) {
+               int chan;
+               for (chan = 0; chan < 4; chan++) {
+                       rc_swizzle swz =
+                               get_swz(inst->U.I.SrcReg[i].Swizzle, chan);
+                       if (swz == RC_SWIZZLE_ONE
+                                       || swz == RC_SWIZZLE_ZERO
+                                       || swz == RC_SWIZZLE_HALF) {
+                               is_constant[i] = 1;
+                       }
+               }
+       }
+       if (is_constant[0] && is_constant[1])
+               return 0;
+
        for(i = 0; i < info->NumSrcRegs; i++) {
                struct rc_src_register src = inst->U.I.SrcReg[i];
                if (src_reads_dst_mask(src, inst->U.I.DstReg))