Mesa (master): broadcom/vc5: Remove no-op MOVs after register allocation.

[Eric Anholt]

Module: Mesa
Branch: master
Commit: dc78643ace0125f5dea4b620c0dffcf5736584b2
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=dc78643ace0125f5dea4b620c0dffcf5736584b2

Author: Eric Anholt <eric at anholt.net>
Date:   Sun Feb  4 21:05:03 2018 +0000

broadcom/vc5: Remove no-op MOVs after register allocation.

We emit some MOVs to track lifetimes of payload registers, but we don't
need there to be actual MOV instructions for them.

total instructions in shared programs: 101045 -> 100423 (-0.62%)
instructions in affected programs:     37083 -> 36461 (-1.68%)

---

 src/broadcom/compiler/vir_to_qpu.c | 61 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 60 insertions(+), 1 deletion(-)

diff --git a/src/broadcom/compiler/vir_to_qpu.c b/src/broadcom/compiler/vir_to_qpu.c
index 11a7ef9103..568a004803 100644
--- a/src/broadcom/compiler/vir_to_qpu.c
+++ b/src/broadcom/compiler/vir_to_qpu.c
@@ -138,6 +138,60 @@ set_src(struct v3d_qpu_instr *instr, enum v3d_qpu_mux *mux, struct qpu_reg src)
         }
 }
 
+static bool
+is_no_op_mov(struct qinst *qinst)
+{
+        static const struct v3d_qpu_sig no_sig = {0};
+
+        /* Make sure it's just a lone MOV. */
+        if (qinst->qpu.type != V3D_QPU_INSTR_TYPE_ALU ||
+            qinst->qpu.alu.mul.op != V3D_QPU_M_MOV ||
+            qinst->qpu.alu.add.op != V3D_QPU_A_NOP ||
+            memcmp(&qinst->qpu.sig, &no_sig, sizeof(no_sig)) != 0) {
+                return false;
+        }
+
+        /* Check if it's a MOV from a register to itself. */
+        enum v3d_qpu_waddr waddr = qinst->qpu.alu.mul.waddr;
+        if (qinst->qpu.alu.mul.magic_write) {
+                if (waddr < V3D_QPU_WADDR_R0 || waddr > V3D_QPU_WADDR_R4)
+                        return false;
+
+                if (qinst->qpu.alu.mul.a !=
+                    V3D_QPU_MUX_R0 + (waddr - V3D_QPU_WADDR_R0)) {
+                        return false;
+                }
+        } else {
+                int raddr;
+
+                switch (qinst->qpu.alu.mul.a) {
+                case V3D_QPU_MUX_A:
+                        raddr = qinst->qpu.raddr_a;
+                        break;
+                case V3D_QPU_MUX_B:
+                        raddr = qinst->qpu.raddr_b;
+                        break;
+                default:
+                        return false;
+                }
+                if (raddr != waddr)
+                        return false;
+        }
+
+        /* No packing or flags updates, or we need to execute the
+         * instruction.
+         */
+        if (qinst->qpu.alu.mul.a_unpack != V3D_QPU_UNPACK_NONE ||
+            qinst->qpu.alu.mul.output_pack != V3D_QPU_PACK_NONE ||
+            qinst->qpu.flags.mc != V3D_QPU_COND_NONE ||
+            qinst->qpu.flags.mpf != V3D_QPU_PF_NONE ||
+            qinst->qpu.flags.muf != V3D_QPU_UF_NONE) {
+                return false;
+        }
+
+        return true;
+}
+
 static void
 v3d_generate_code_block(struct v3d_compile *c,
                         struct qblock *block,
@@ -145,7 +199,7 @@ v3d_generate_code_block(struct v3d_compile *c,
 {
         int last_vpm_read_index = -1;
 
-        vir_for_each_inst(qinst, block) {
+        vir_for_each_inst_safe(qinst, block) {
 #if 0
                 fprintf(stderr, "translating qinst to qpu: ");
                 vir_dump_inst(c, qinst);
@@ -289,6 +343,11 @@ v3d_generate_code_block(struct v3d_compile *c,
 
                                 qinst->qpu.alu.mul.waddr = dst.index;
                                 qinst->qpu.alu.mul.magic_write = dst.magic;
+
+                                if (is_no_op_mov(qinst)) {
+                                        vir_remove_instruction(c, qinst);
+                                        continue;
+                                }
                         }
                 } else {
                         assert(qinst->qpu.type == V3D_QPU_INSTR_TYPE_BRANCH);