[Mesa-dev] [PATCH 08/16] i965/fs: Add a pass to fixup 3-src instructions that have a null dest.

[Matt Turner]

3-src instructions can only have GRF/MRF destinations. It's really
difficult to deal with that restriction in dead code elimination (that
wants to give instructions null destinations to show that their result
isn't used) while allowing 3-src instructions to have conditional mod,
so don't, and just give then a destination before register allocation.
---
 src/mesa/drivers/dri/i965/brw_fs.cpp | 14 ++++++++++++++
 src/mesa/drivers/dri/i965/brw_fs.h   |  1 +
 2 files changed, 15 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 35639de..73d722e 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -3605,6 +3605,18 @@ fs_visitor::optimize()
 }
 
 void
+fs_visitor::fixup_3src_null_dest()
+{
+   foreach_block_and_inst_safe (block, fs_inst, inst, cfg) {
+      if (inst->is_3src() && inst->dst.is_null()) {
+         /* 3-src instructions can only have GRF/MRF destination. */
+         inst->dst = fs_reg(GRF, virtual_grf_alloc(dispatch_width / 8),
+                            inst->dst.type);
+      }
+   }
+}
+
+void
 fs_visitor::allocate_registers()
 {
    bool allocated_without_spills;
@@ -3701,6 +3713,7 @@ fs_visitor::run_vs()
    assign_curb_setup();
    assign_vs_urb_setup();
 
+   fixup_3src_null_dest();
    allocate_registers();
 
    return !failed;
@@ -3780,6 +3793,7 @@ fs_visitor::run_fs()
       assign_curb_setup();
       assign_urb_setup();
 
+      fixup_3src_null_dest();
       allocate_registers();
 
       if (failed)
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 2aa58eb..9c125a6 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -423,6 +423,7 @@ public:
    void setup_payload_gen4();
    void setup_payload_gen6();
    void setup_vs_payload();
+   void fixup_3src_null_dest();
    void assign_curb_setup();
    void calculate_urb_setup();
    void assign_urb_setup();
-- 
2.0.4