nir/from_ssa: add a flag to not convert everything from SSA

We already don't convert constants out of SSA, and in our backend we'd
like to have only one way of saying something is still in SSA.

The one tricky part about this is that we may now leave some undef
instructions around if they aren't part of a phi-web, so we have to be
more careful about deleting them.

v2: rename and flip meaning of flag (Jason)

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>

diff --git a/src/gallium/drivers/vc4/vc4_program.c b/src/gallium/drivers/vc4/vc4_program.c
index 2061631dc9e1f6bd8a1e885762db766d03bcec83..7b39a03f01a7102ff480faf945717a637dbb07db 100644 (file)
--- a/src/gallium/drivers/vc4/vc4_program.c
+++ b/src/gallium/drivers/vc4/vc4_program.c
@@ -2102,7 +2102,7 @@ vc4_shader_ntq(struct vc4_context *vc4, enum qstage stage,
 
         nir_remove_dead_variables(c->s);
 
-        nir_convert_from_ssa(c->s);
+        nir_convert_from_ssa(c->s, false);
 
         if (vc4_debug & VC4_DEBUG_SHADERDB) {
                 fprintf(stderr, "SHADER-DB: %s prog %d/%d: %d NIR instructions\n",

diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
index 697d37e95acd14131abe9fea87c636aa593aed72..8c99845f04df10952b09344e0441c12f27780efd 100644 (file)
--- a/src/glsl/nir/nir.h
+++ b/src/glsl/nir/nir.h
@@ -1676,7 +1676,12 @@ bool nir_ssa_defs_interfere(nir_ssa_def *a, nir_ssa_def *b);
 
 void nir_convert_to_ssa_impl(nir_function_impl *impl);
 void nir_convert_to_ssa(nir_shader *shader);
-void nir_convert_from_ssa(nir_shader *shader);
+
+/* If convert_everything is true, convert all values (even those not involved
+ * in a phi node) to registers. If false, only convert SSA values involved in
+ * phi nodes to registers.
+ */
+void nir_convert_from_ssa(nir_shader *shader, bool phi_webs_only);
 
 bool nir_opt_algebraic(nir_shader *shader);
 bool nir_opt_algebraic_late(nir_shader *shader);

diff --git a/src/glsl/nir/nir_from_ssa.c b/src/glsl/nir/nir_from_ssa.c
index 67733e6da4f4d70241ccc83422bedadeb7f9b9f9..e4a153e958471a176d804a550d32a591be6892fe 100644 (file)
--- a/src/glsl/nir/nir_from_ssa.c
+++ b/src/glsl/nir/nir_from_ssa.c
@@ -37,6 +37,7 @@
 struct from_ssa_state {
    void *mem_ctx;
    void *dead_ctx;
+   bool phi_webs_only;
    struct hash_table *merge_node_table;
    nir_instr *instr;
    nir_function_impl *impl;
@@ -482,6 +483,9 @@ rewrite_ssa_def(nir_ssa_def *def, void *void_state)
 
       reg = node->set->reg;
    } else {
+      if (state->phi_webs_only)
+         return true;
+
       /* We leave load_const SSA values alone.  They act as immediates to
        * the backend.  If it got coalesced into a phi, that's ok.
        */
@@ -505,8 +509,15 @@ rewrite_ssa_def(nir_ssa_def *def, void *void_state)
    nir_ssa_def_rewrite_uses(def, nir_src_for_reg(reg), state->mem_ctx);
    assert(list_empty(&def->uses) && list_empty(&def->if_uses));
 
-   if (def->parent_instr->type == nir_instr_type_ssa_undef)
+   if (def->parent_instr->type == nir_instr_type_ssa_undef) {
+      /* If it's an ssa_undef instruction, remove it since we know we just got
+       * rid of all its uses.
+       */
+      nir_instr *parent_instr = def->parent_instr;
+      nir_instr_remove(parent_instr);
+      ralloc_steal(state->dead_ctx, parent_instr);
       return true;
+   }
 
    assert(def->parent_instr->type != nir_instr_type_load_const);
 
@@ -523,7 +534,7 @@ rewrite_ssa_def(nir_ssa_def *def, void *void_state)
 }
 
 /* Resolves ssa definitions to registers.  While we're at it, we also
- * remove phi nodes and ssa_undef instructions
+ * remove phi nodes.
  */
 static bool
 resolve_registers_block(nir_block *block, void *void_state)
@@ -534,8 +545,7 @@ resolve_registers_block(nir_block *block, void *void_state)
       state->instr = instr;
       nir_foreach_ssa_def(instr, rewrite_ssa_def, state);
 
-      if (instr->type == nir_instr_type_ssa_undef ||
-          instr->type == nir_instr_type_phi) {
+      if (instr->type == nir_instr_type_phi) {
          nir_instr_remove(instr);
          ralloc_steal(state->dead_ctx, instr);
       }
@@ -765,13 +775,14 @@ resolve_parallel_copies_block(nir_block *block, void *void_state)
 }
 
 static void
-nir_convert_from_ssa_impl(nir_function_impl *impl)
+nir_convert_from_ssa_impl(nir_function_impl *impl, bool phi_webs_only)
 {
    struct from_ssa_state state;
 
    state.mem_ctx = ralloc_parent(impl);
    state.dead_ctx = ralloc_context(NULL);
    state.impl = impl;
+   state.phi_webs_only = phi_webs_only;
    state.merge_node_table = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
                                                     _mesa_key_pointer_equal);
 
@@ -801,10 +812,10 @@ nir_convert_from_ssa_impl(nir_function_impl *impl)
 }
 
 void
-nir_convert_from_ssa(nir_shader *shader)
+nir_convert_from_ssa(nir_shader *shader, bool phi_webs_only)
 {
    nir_foreach_overload(shader, overload) {
       if (overload->impl)
-         nir_convert_from_ssa_impl(overload->impl);
+         nir_convert_from_ssa_impl(overload->impl, phi_webs_only);
    }
 }

diff --git a/src/mesa/drivers/dri/i965/brw_nir.c b/src/mesa/drivers/dri/i965/brw_nir.c
index dffb8ab1ca72efa0c5e081604ad6a480b3ded9ca..d87e78312fd4eb4498fb2451b7788e85d398df38 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_nir.c
+++ b/src/mesa/drivers/dri/i965/brw_nir.c
@@ -156,7 +156,7 @@ brw_create_nir(struct brw_context *brw,
       nir_print_shader(nir, stderr);
    }
 
-   nir_convert_from_ssa(nir);
+   nir_convert_from_ssa(nir, false);
    nir_validate_shader(nir);
 
    /* This is the last pass we run before we start emitting stuff.  It