Mesa (master): i965/vs: Add simple dead code elimination.
Eric Anholt
anholt at kemper.freedesktop.org
Sat Aug 20 00:14:10 UTC 2011
Module: Mesa
Branch: master
Commit: 8174945d3346dc049ae56dcb4bf1eab39f5c88aa
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=8174945d3346dc049ae56dcb4bf1eab39f5c88aa
Author: Eric Anholt <eric at anholt.net>
Date: Wed Aug 17 10:50:17 2011 -0700
i965/vs: Add simple dead code elimination.
This is copied right from the fragment shader. It is needed for real
register allocation to work correctly.
---
src/mesa/drivers/dri/i965/brw_vec4.cpp | 31 +++++++++++++++++++++++++++
src/mesa/drivers/dri/i965/brw_vec4.h | 1 +
src/mesa/drivers/dri/i965/brw_vec4_emit.cpp | 6 +++++
3 files changed, 38 insertions(+), 0 deletions(-)
diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
index a3ed31a..760bc1f 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
@@ -127,4 +127,35 @@ vec4_visitor::virtual_grf_interferes(int a, int b)
return start < end;
}
+/**
+ * Must be called after calculate_live_intervales() to remove unused
+ * writes to registers -- register allocation will fail otherwise
+ * because something deffed but not used won't be considered to
+ * interfere with other regs.
+ */
+bool
+vec4_visitor::dead_code_eliminate()
+{
+ bool progress = false;
+ int pc = 0;
+
+ calculate_live_intervals();
+
+ foreach_list_safe(node, &this->instructions) {
+ vec4_instruction *inst = (vec4_instruction *)node;
+
+ if (inst->dst.file == GRF && this->virtual_grf_use[inst->dst.reg] <= pc) {
+ inst->remove();
+ progress = true;
+ }
+
+ pc++;
+ }
+
+ if (progress)
+ live_intervals_valid = false;
+
+ return progress;
+}
+
} /* namespace brw */
diff --git a/src/mesa/drivers/dri/i965/brw_vec4.h b/src/mesa/drivers/dri/i965/brw_vec4.h
index 77a28c7..1db910e 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4.h
+++ b/src/mesa/drivers/dri/i965/brw_vec4.h
@@ -381,6 +381,7 @@ public:
void reg_allocate();
void move_grf_array_access_to_scratch();
void calculate_live_intervals();
+ bool dead_code_eliminate();
bool virtual_grf_interferes(int a, int b);
vec4_instruction *emit(enum opcode opcode);
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
index 011af6f..65ac7d9 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_emit.cpp
@@ -558,6 +558,12 @@ vec4_visitor::run()
*/
move_grf_array_access_to_scratch();
+ bool progress;
+ do {
+ progress = false;
+ progress = dead_code_eliminate() || progress;
+ } while (progress);
+
if (failed)
return false;
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