nir: Add a loop analysis pass

This pass detects induction variables and calculates the
trip count of loops to be used for loop unrolling.

V2: Rebase, adapt to removal of function overloads

V3: (Timothy Arceri)
 - don't try to find trip count if loop terminator conditional is a phi
 - fix trip count for do-while loops
 - replace conditional type != alu assert with return
 - disable unrolling of loops with continues
 - multiple fixes to memory allocation, stop leaking and don't destroy
   structs we want to use for unrolling.
 - fix iteration count bugs when induction var not on RHS of condition
 - add FIXME for && conditions
 - calculate trip count for unsigned induction/limit vars

V4: (Timothy Arceri)
- count instructions in a loop
- set the limiting_terminator even if we can't find the trip count for
 all terminators. This is needed for complex unrolling where we handle
 2 terminators and the trip count is unknown for one of them.
- restruct structs so we don't keep information not required after
 analysis and remove dead fields.
- force unrolling in some cases as per the rules in the GLSL IR pass

V5: (Timothy Arceri)
- fix metadata mask value 0x10 vs 0x16

V6: (Timothy Arceri)
- merge loop_variable and nir_loop_variable structs and lists suggested by Jason
- remove induction var hash table and store pointer to induction information in
  the loop_variable suggested by Jason.
- use lowercase list_addtail() suggested by Jason.
- tidy up init_loop_block() as per Jasons suggestions.
- replace switch with nir_op_infos[alu->op].num_inputs == 2 in
  is_var_basic_induction_var() as suggested by Jason.
- use nir_block_last_instr() in and rename foreach_cf_node_ex_loop() as suggested
  by Jason.
- fix else check for is_trivial_loop_terminator() as per Connors suggetions.
- simplify offset for induction valiables incremented before the exit conditions is
  checked.
- replace nir_op_isub check with assert() as it should have been lowered away.

V7: (Timothy Arceri)
- use rzalloc() on nir_loop struct creation. Worked previously because ralloc()
  was broken and always zeroed the struct.
- fix cf_node_find_loop_jumps() to find jumps when loops contain
  nested if statements. Code is tidier as a result.

V8: (Timothy Arceri)
- move is_trivial_loop_terminator() to nir.h so we can use it to assert is
  the loop unroll pass
- fix analysis to not bail when looking for terminator when the break is in the else
  rather then the if
- added new loop terminator fields: break_block, continue_from_block and
  continue_from_then so we don't have to gather these when doing unrolling.
- get correct array length when forcing unrolling of variables
  indexed arrays that are the same size as the iteration count
- add support for induction variables of type float
- update trival loop terminator check to allow an if containing
  instructions as long as both branches contain only a single
  block.

V9: (Timothy)
 - bunch of tidy ups and simplifications suggested by Jason.
 - rewrote trivial terminator detection, now the only restriction is there
   must be no nested jumps, anything else goes.
 - rewrote the iteration test to use nir_eval_const_opcode().
 - count instruction properly even when forcing an unroll.
 - bunch of other tidy ups and simplifications.

V10: (Timothy)
 - some trivial tidy ups suggested by Jason.
 - conditional fix for break inside continue branch by Jason.

Reviewed-by: Jason Ekstrand <[email protected]>

1 files changed, 92 insertions, 0 deletions

diff --git a/src/compiler/nir/nir_loop_analyze.h b/src/compiler/nir/nir_loop_analyze.h
new file mode 100644
index 00000000000..b7f862e8c04
--- /dev/null
+++ b/src/compiler/nir/nir_loop_analyze.h
@@ -0,0 +1,92 @@
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#pragma once
+
+#include "nir.h"
+
+/* Returns true if nir_cf_node contains a jump other than the expected_jump
+ * parameter.
+ */
+static inline bool
+contains_other_jump(nir_cf_node *node, nir_instr *expected_jump)
+{
+   switch (node->type) {
+   case nir_cf_node_block: {
+      nir_instr *lst_instr = nir_block_last_instr(nir_cf_node_as_block(node));
+
+      /* dead_cf should have eliminated any instruction after the first break
+       */
+      nir_foreach_instr(instr, nir_cf_node_as_block(node))
+         assert(instr->type != nir_instr_type_jump || instr == lst_instr);
+
+      if (lst_instr && lst_instr->type == nir_instr_type_jump &&
+          lst_instr != expected_jump)
+         return true;
+      else
+         return false;
+   }
+   case nir_cf_node_if: {
+      nir_if *if_stmt = nir_cf_node_as_if(node);
+
+      foreach_list_typed_safe(nir_cf_node, node, node, &if_stmt->then_list) {
+         if (contains_other_jump(node, expected_jump))
+            return true;
+      }
+
+      foreach_list_typed_safe(nir_cf_node, node, node, &if_stmt->else_list) {
+         if (contains_other_jump(node, expected_jump))
+            return true;
+      }
+
+      return false;
+   }
+   case nir_cf_node_loop:
+      return true;
+
+   default:
+      unreachable("Unhandled cf node type");
+   }
+}
+
+/* Here we define a trivial if as containing only a single break that must be
+ * located at the end of either the then or else branch of the top level if,
+ * there must be no other breaks or any other type of jump.  Or we pass NULL
+ * to break_block the if must contains no jumps at all.
+ */
+static inline bool
+nir_is_trivial_loop_if(nir_if *nif, nir_block *break_block)
+{
+   nir_instr *last_instr = NULL;
+
+   if (break_block) {
+      last_instr = nir_block_last_instr(break_block);
+      assert(last_instr && last_instr->type == nir_instr_type_jump &&
+             nir_instr_as_jump(last_instr)->type == nir_jump_break);
+   }
+
+   if (contains_other_jump(&nif->cf_node, last_instr))
+      return false;
+
+   return true;
+}