Mesa (master): i965/fs: Eliminate the magic nature of virtual GRF 0.

Eric Anholt anholt at kemper.freedesktop.org
Wed Aug 10 11:16:51 PDT 2011


Module: Mesa
Branch: master
Commit: b76378d46a211521582cfab56dc05031a57502a6
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=b76378d46a211521582cfab56dc05031a57502a6

Author: Eric Anholt <eric at anholt.net>
Date:   Wed May  4 13:50:13 2011 -0700

i965/fs: Eliminate the magic nature of virtual GRF 0.

This was a debugging aid at one point -- virtual grf 0 should never be
allocated, and it would be used if undefined register access occurred
in codegen.  However, it made the confusing register allocation code
even more confusing by indexing things off of 1 all over.

---

 src/mesa/drivers/dri/i965/brw_fs.cpp              |    9 ++----
 src/mesa/drivers/dri/i965/brw_fs.h                |    2 +-
 src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp |   33 +++++++-------------
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp      |    4 +--
 4 files changed, 17 insertions(+), 31 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index f55be02..d57a67c 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -181,9 +181,6 @@ fs_visitor::virtual_grf_alloc(int size)
 	 virtual_grf_array_size *= 2;
       virtual_grf_sizes = reralloc(mem_ctx, virtual_grf_sizes, int,
 				   virtual_grf_array_size);
-
-      /* This slot is always unused. */
-      virtual_grf_sizes[0] = 0;
    }
    virtual_grf_sizes[virtual_grf_next] = size;
    return virtual_grf_next++;
@@ -985,7 +982,7 @@ fs_visitor::calculate_live_intervals()
 	 }
       } else {
 	 for (unsigned int i = 0; i < 3; i++) {
-	    if (inst->src[i].file == GRF && inst->src[i].reg != 0) {
+	    if (inst->src[i].file == GRF) {
 	       int reg = inst->src[i].reg;
 
 	       if (!loop_depth) {
@@ -1001,7 +998,7 @@ fs_visitor::calculate_live_intervals()
 	       }
 	    }
 	 }
-	 if (inst->dst.file == GRF && inst->dst.reg != 0) {
+	 if (inst->dst.file == GRF) {
 	    int reg = inst->dst.reg;
 
 	    if (!loop_depth) {
@@ -1715,7 +1712,7 @@ fs_visitor::run()
       if (0) {
 	 /* Debug of register spilling: Go spill everything. */
 	 int virtual_grf_count = virtual_grf_next;
-	 for (int i = 1; i < virtual_grf_count; i++) {
+	 for (int i = 0; i < virtual_grf_count; i++) {
 	    spill_reg(i);
 	 }
       }
diff --git a/src/mesa/drivers/dri/i965/brw_fs.h b/src/mesa/drivers/dri/i965/brw_fs.h
index 96e1420..0375f67 100644
--- a/src/mesa/drivers/dri/i965/brw_fs.h
+++ b/src/mesa/drivers/dri/i965/brw_fs.h
@@ -402,7 +402,7 @@ public:
       this->base_ir = NULL;
 
       this->virtual_grf_sizes = NULL;
-      this->virtual_grf_next = 1;
+      this->virtual_grf_next = 0;
       this->virtual_grf_array_size = 0;
       this->virtual_grf_def = NULL;
       this->virtual_grf_use = NULL;
diff --git a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
index f246ac4..83dd629 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_reg_allocate.cpp
@@ -50,7 +50,7 @@ extern "C" {
 static void
 assign_reg(int *reg_hw_locations, fs_reg *reg, int reg_width)
 {
-   if (reg->file == GRF && reg->reg != 0) {
+   if (reg->file == GRF) {
       assert(reg->reg_offset >= 0);
       reg->hw_reg = reg_hw_locations[reg->reg] + reg->reg_offset * reg_width;
       reg->reg = 0;
@@ -60,20 +60,17 @@ assign_reg(int *reg_hw_locations, fs_reg *reg, int reg_width)
 void
 fs_visitor::assign_regs_trivial()
 {
-   int last_grf = 0;
-   int hw_reg_mapping[this->virtual_grf_next];
+   int hw_reg_mapping[this->virtual_grf_next + 1];
    int i;
    int reg_width = c->dispatch_width / 8;
 
-   hw_reg_mapping[0] = 0;
    /* Note that compressed instructions require alignment to 2 registers. */
-   hw_reg_mapping[1] = ALIGN(this->first_non_payload_grf, reg_width);
-   for (i = 2; i < this->virtual_grf_next; i++) {
+   hw_reg_mapping[0] = ALIGN(this->first_non_payload_grf, reg_width);
+   for (i = 1; i <= this->virtual_grf_next; i++) {
       hw_reg_mapping[i] = (hw_reg_mapping[i - 1] +
 			   this->virtual_grf_sizes[i - 1] * reg_width);
    }
-   last_grf = hw_reg_mapping[i - 1] + (this->virtual_grf_sizes[i - 1] *
-				       reg_width);
+   this->grf_used = hw_reg_mapping[this->virtual_grf_next];
 
    foreach_list(node, &this->instructions) {
       fs_inst *inst = (fs_inst *)node;
@@ -83,12 +80,11 @@ fs_visitor::assign_regs_trivial()
       assign_reg(hw_reg_mapping, &inst->src[1], reg_width);
    }
 
-   if (last_grf >= BRW_MAX_GRF) {
+   if (this->grf_used >= BRW_MAX_GRF) {
       fail("Ran out of regs on trivial allocator (%d/%d)\n",
-	   last_grf, BRW_MAX_GRF);
+	   this->grf_used, BRW_MAX_GRF);
    }
 
-   this->grf_used = last_grf + reg_width;
 }
 
 bool
@@ -101,7 +97,7 @@ fs_visitor::assign_regs()
     * for reg_width == 2.
     */
    int reg_width = c->dispatch_width / 8;
-   int hw_reg_mapping[this->virtual_grf_next + 1];
+   int hw_reg_mapping[this->virtual_grf_next];
    int first_assigned_grf = ALIGN(this->first_non_payload_grf, reg_width);
    int base_reg_count = (BRW_MAX_GRF - first_assigned_grf) / reg_width;
    int class_sizes[base_reg_count];
@@ -125,7 +121,7 @@ fs_visitor::assign_regs()
        */
       class_sizes[class_count++] = 2;
    }
-   for (int r = 1; r < this->virtual_grf_next; r++) {
+   for (int r = 0; r < this->virtual_grf_next; r++) {
       int i;
 
       for (i = 0; i < class_count; i++) {
@@ -195,12 +191,8 @@ fs_visitor::assign_regs()
 
    struct ra_graph *g = ra_alloc_interference_graph(regs,
 						    this->virtual_grf_next);
-   /* Node 0 is just a placeholder to keep virtual_grf[] mapping 1:1
-    * with nodes.
-    */
-   ra_set_node_class(g, 0, classes[0]);
 
-   for (int i = 1; i < this->virtual_grf_next; i++) {
+   for (int i = 0; i < this->virtual_grf_next; i++) {
       for (int c = 0; c < class_count; c++) {
 	 if (class_sizes[c] == this->virtual_grf_sizes[i]) {
 	    if (aligned_pair_class >= 0 &&
@@ -213,7 +205,7 @@ fs_visitor::assign_regs()
 	 }
       }
 
-      for (int j = 1; j < i; j++) {
+      for (int j = 0; j < i; j++) {
 	 if (virtual_grf_interferes(i, j)) {
 	    ra_add_node_interference(g, i, j);
 	 }
@@ -248,8 +240,7 @@ fs_visitor::assign_regs()
     * numbers.
     */
    this->grf_used = first_assigned_grf;
-   hw_reg_mapping[0] = 0; /* unused */
-   for (int i = 1; i < this->virtual_grf_next; i++) {
+   for (int i = 0; i < this->virtual_grf_next; i++) {
       int reg = ra_get_node_reg(g, i);
       int hw_reg = -1;
 
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 2b769cc..2e3f9be 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -142,9 +142,7 @@ fs_visitor::visit(ir_dereference_array *ir)
    this->result.type = brw_type_for_base_type(ir->type);
 
    if (index) {
-      assert(this->result.file == UNIFORM ||
-	     (this->result.file == GRF &&
-	      this->result.reg != 0));
+      assert(this->result.file == UNIFORM || this->result.file == GRF);
       this->result.reg_offset += index->value.i[0] * element_size;
    } else {
       assert(!"FINISHME: non-constant array element");



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