Mesa (master): i965/cfg: Track prev_block and prev_inst explicitly in the whole function

[Ian Romanick]

Module: Mesa
Branch: master
Commit: c7deee69ea6f64ea5b563985bf19d9deebe73b5b
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=c7deee69ea6f64ea5b563985bf19d9deebe73b5b

Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Wed Feb 24 19:26:13 2016 -0800

i965/cfg: Track prev_block and prev_inst explicitly in the whole function

This provides a trivial simplification now, and it makes some future
changes more straight forward.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Reviewed-by: Francisco Jerez <currojerez at riseup.net>

---

 src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp b/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
index 716e2bc..7aa72b1 100644
--- a/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
+++ b/src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
@@ -41,7 +41,9 @@ dead_control_flow_eliminate(backend_shader *s)
    bool progress = false;
 
    foreach_block_safe (block, s->cfg) {
+      bblock_t *prev_block = block->prev();
       backend_instruction *const inst = block->start();
+      backend_instruction *prev_inst = prev_block->end();
 
       /* ENDIF instructions, by definition, can only be found at the start of
        * basic blocks.
@@ -52,20 +54,20 @@ dead_control_flow_eliminate(backend_shader *s)
          backend_instruction *endif_inst = inst;
 
          backend_instruction *if_inst = NULL, *else_inst = NULL;
-         backend_instruction *prev_inst = endif_block->prev()->end();
          if (prev_inst->opcode == BRW_OPCODE_ELSE) {
             else_inst = prev_inst;
             else_block = endif_block->prev();
             found = true;
 
-            if (else_block->start_ip == else_block->end_ip)
-               prev_inst = else_block->prev()->end();
+            if (else_block->start_ip == else_block->end_ip) {
+               prev_block = prev_block->prev();
+               prev_inst = prev_block->end();
+            }
          }
 
          if (prev_inst->opcode == BRW_OPCODE_IF) {
             if_inst = prev_inst;
-            if_block = else_block != NULL ? else_block->prev()
-               : endif_block->prev();
+            if_block = prev_block;
             found = true;
          } else {
             /* Don't remove the ENDIF if we didn't find a dead IF. */