Mesa (glsl2): glsl2: Catch pointless copies in copy propagation.
Eric Anholt
anholt at kemper.freedesktop.org
Thu Aug 5 16:22:50 UTC 2010
Module: Mesa
Branch: glsl2
Commit: c5b9cab49900cbcab78911361976a3678d49e853
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=c5b9cab49900cbcab78911361976a3678d49e853
Author: Eric Anholt <eric at anholt.net>
Date: Wed Aug 4 23:23:15 2010 -0700
glsl2: Catch pointless copies in copy propagation.
We wouldn't want to go rewriting dereferences to variables to point at
the same variable it did before. While I didn't find a way to trigger
that, a shader in Yo Frankie managed to produce a self-assignment by
passing a constant to a function doing self assignment like this.
Cleans up the IR for glsl-deadcode-self-assign.shader_test
---
src/glsl/ir_copy_propagation.cpp | 22 +++++++++++++++++-----
1 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/src/glsl/ir_copy_propagation.cpp b/src/glsl/ir_copy_propagation.cpp
index 26588a3..1d28392 100644
--- a/src/glsl/ir_copy_propagation.cpp
+++ b/src/glsl/ir_copy_propagation.cpp
@@ -213,7 +213,7 @@ kill_invalidated_copies(ir_assignment *ir, exec_list *acp)
* Adds an entry to the available copy list if it's a plain assignment
* of a variable to a variable.
*/
-static void
+static bool
add_copy(void *ctx, ir_assignment *ir, exec_list *acp)
{
acp_entry *entry;
@@ -221,16 +221,28 @@ add_copy(void *ctx, ir_assignment *ir, exec_list *acp)
if (ir->condition) {
ir_constant *condition = ir->condition->as_constant();
if (!condition || !condition->value.b[0])
- return;
+ return false;
}
ir_variable *lhs_var = ir->whole_variable_written();
ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
if ((lhs_var != NULL) && (rhs_var != NULL)) {
- entry = new(ctx) acp_entry(lhs_var, rhs_var);
- acp->push_tail(entry);
+ if (lhs_var == rhs_var) {
+ /* This is a dumb assignment, but we've conveniently noticed
+ * it here. Removing it now would mess up the loop iteration
+ * calling us. Just flag it to not execute, and someone else
+ * will clean up the mess.
+ */
+ ir->condition = new(talloc_parent(ir)) ir_constant(false);
+ return true;
+ } else {
+ entry = new(ctx) acp_entry(lhs_var, rhs_var);
+ acp->push_tail(entry);
+ }
}
+
+ return false;
}
static void
@@ -253,7 +265,7 @@ copy_propagation_basic_block(ir_instruction *first,
if (ir_assign) {
kill_invalidated_copies(ir_assign, &acp);
- add_copy(ctx, ir_assign, &acp);
+ progress = add_copy(ctx, ir_assign, &acp) || progress;
}
if (ir == last)
break;
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