[Mesa-dev] [PATCH v2 1/3] glsl: don't drop instructions from unreachable terminators continue branch

[Timothy Arceri]

These instructions will be executed on every iteration of the loop
we cannot drop them.

V2:
- move removal of unreachable terminators from the terminator list
  to the same place they are removed from the IR as suggested by
  Nicolai.
---
 src/compiler/glsl/loop_analysis.h |  7 +++++++
 src/compiler/glsl/loop_unroll.cpp | 28 ++++++++++++++++++++--------
 2 files changed, 27 insertions(+), 8 deletions(-)

diff --git a/src/compiler/glsl/loop_analysis.h b/src/compiler/glsl/loop_analysis.h
index 8f82404694..99b6bf7563 100644
--- a/src/compiler/glsl/loop_analysis.h
+++ b/src/compiler/glsl/loop_analysis.h
@@ -27,20 +27,27 @@
 
 #include "ir.h"
 #include "util/hash_table.h"
 
 /**
  * Analyze and classify all variables used in all loops in the instruction list
  */
 extern class loop_state *
 analyze_loop_variables(exec_list *instructions);
 
+static inline bool
+is_break(ir_instruction *ir)
+{
+   return ir != NULL && ir->ir_type == ir_type_loop_jump &&
+      ((ir_loop_jump *) ir)->is_break();
+}
+
 
 extern bool
 unroll_loops(exec_list *instructions, loop_state *ls,
              const struct gl_shader_compiler_options *options);
 
 
 /**
  * Tracking for all variables used in a loop
  */
 class loop_variable_state : public exec_node {
diff --git a/src/compiler/glsl/loop_unroll.cpp b/src/compiler/glsl/loop_unroll.cpp
index 7eea439454..358cbf10af 100644
--- a/src/compiler/glsl/loop_unroll.cpp
+++ b/src/compiler/glsl/loop_unroll.cpp
@@ -46,27 +46,20 @@ public:
    void splice_post_if_instructions(ir_if *ir_if, exec_list *splice_dest);
 
    loop_state *state;
 
    bool progress;
    const struct gl_shader_compiler_options *options;
 };
 
 } /* anonymous namespace */
 
-static bool
-is_break(ir_instruction *ir)
-{
-   return ir != NULL && ir->ir_type == ir_type_loop_jump
-		     && ((ir_loop_jump *) ir)->is_break();
-}
-
 class loop_unroll_count : public ir_hierarchical_visitor {
 public:
    int nodes;
    bool unsupported_variable_indexing;
    bool array_indexed_by_induction_var_with_exact_iterations;
    /* If there are nested loops, the node count will be inaccurate. */
    bool nested_loop;
 
    loop_unroll_count(exec_list *list, loop_variable_state *ls,
                      const struct gl_shader_compiler_options *options)
@@ -326,30 +319,49 @@ loop_unroll_visitor::visit_leave(ir_loop *ir)
       }
    }
 
    /* Remove the conditional break statements associated with all terminators
     * that are associated with a fixed iteration count, except for the one
     * associated with the limiting terminator--that one needs to stay, since
     * it terminates the loop.  Exception: if the loop still has a normative
     * bound, then that terminates the loop, so we don't even need the limiting
     * terminator.
     */
-   foreach_in_list(loop_terminator, t, &ls->terminators) {
+   foreach_in_list_safe(loop_terminator, t, &ls->terminators) {
       if (t->iterations < 0)
          continue;
 
+      exec_list *branch_instructions;
       if (t != ls->limiting_terminator) {
+         ir_instruction *ir_if_last = (ir_instruction *)
+            t->ir->then_instructions.get_tail();
+         if (is_break(ir_if_last)) {
+            branch_instructions = &t->ir->else_instructions;
+         } else {
+            branch_instructions = &t->ir->then_instructions;
+            assert(is_break((ir_instruction *)
+                            t->ir->else_instructions.get_tail()));
+         }
+
+         exec_list copy_list;
+         copy_list.make_empty();
+         clone_ir_list(ir, &copy_list, branch_instructions);
+
+         t->ir->insert_before(&copy_list);
          t->ir->remove();
 
          assert(ls->num_loop_jumps > 0);
          ls->num_loop_jumps--;
 
+         /* Also remove it from the terminator list */
+         t->remove();
+
          this->progress = true;
       }
    }
 
    if (ls->limiting_terminator == NULL) {
       ir_instruction *last_ir =
          (ir_instruction *) ir->body_instructions.get_tail();
 
       /* If a loop has no induction variable and the last instruction is
        * a break, unroll the loop with a count of 1.  This is the classic
-- 
2.13.5