Mesa (master): glsl: check if induction var incremented before use in terminator
Timothy Arceri
tarceri at kemper.freedesktop.org
Mon Oct 9 23:05:48 UTC 2017
Module: Mesa
Branch: master
Commit: d24e16fe1f63d8f666dd57cfddf8340d439b391a
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=d24e16fe1f63d8f666dd57cfddf8340d439b391a
Author: Timothy Arceri <tarceri at itsqueeze.com>
Date: Thu Sep 21 13:55:56 2017 +1000
glsl: check if induction var incremented before use in terminator
do-while loops can increment the starting value before the
condition is checked. e.g.
do {
ndx++;
} while (ndx < 3);
This commit changes the code to detect this and reduces the
iteration count by 1 if found.
V2: fix terminator spelling
Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>
Reviewed-by: Elie Tournier <elie.tournier at collabora.com>
Tested-by: Dieter Nützel <Dieter at nuetzel-hh.de>
---
src/compiler/glsl/loop_analysis.cpp | 38 +++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/src/compiler/glsl/loop_analysis.cpp b/src/compiler/glsl/loop_analysis.cpp
index 81a07f78f8..78279844dc 100644
--- a/src/compiler/glsl/loop_analysis.cpp
+++ b/src/compiler/glsl/loop_analysis.cpp
@@ -171,6 +171,40 @@ calculate_iterations(ir_rvalue *from, ir_rvalue *to, ir_rvalue *increment,
return (valid_loop) ? iter_value : -1;
}
+static bool
+incremented_before_terminator(ir_loop *loop, ir_variable *var,
+ ir_if *terminator)
+{
+ for (exec_node *node = loop->body_instructions.get_head();
+ !node->is_tail_sentinel();
+ node = node->get_next()) {
+ ir_instruction *ir = (ir_instruction *) node;
+
+ switch (ir->ir_type) {
+ case ir_type_if:
+ if (ir->as_if() == terminator)
+ return false;
+ break;
+
+ case ir_type_assignment: {
+ ir_assignment *assign = ir->as_assignment();
+ ir_variable *assignee = assign->lhs->whole_variable_referenced();
+
+ if (assignee == var) {
+ assert(assign->condition == NULL);
+ return true;
+ }
+
+ break;
+ }
+
+ default:
+ break;
+ }
+ }
+
+ unreachable("Unable to find induction variable");
+}
/**
* Record the fact that the given loop variable was referenced inside the loop.
@@ -582,6 +616,10 @@ loop_analysis::visit_leave(ir_loop *ir)
t->iterations = calculate_iterations(init, limit, lv->increment,
cmp);
+ if (incremented_before_terminator(ir, var, t->ir)) {
+ t->iterations--;
+ }
+
if (t->iterations >= 0 &&
(ls->limiting_terminator == NULL ||
t->iterations < ls->limiting_terminator->iterations)) {
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