Mesa (master): glsl: Rework lowering of non-constant array indexing
Ian Romanick
idr at kemper.freedesktop.org
Sat Jul 23 08:25:08 UTC 2011
Module: Mesa
Branch: master
Commit: 1731ac308631138ca98d34e8b7070c6e3f981939
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=1731ac308631138ca98d34e8b7070c6e3f981939
Author: Ian Romanick <ian.d.romanick at intel.com>
Date: Mon Jul 18 12:18:19 2011 -0700
glsl: Rework lowering of non-constant array indexing
The previous implementation could easily get tricked if the LHS of an
assignment included a non-constant index that was "inside" another
dereference. For example:
mat4 m[2];
m[0][i] = vec4(0.0);
Due to the way it tracked whether the array was being assigned, it
would think that the non-constant index was in an r-value. The new
code fixes that by tracking l-values and r-values differently. The
index is also replaced by cloning the IR and replacing the index
variable instead of the odd way it was done before.
v2: Apply some simplifications suggested by Eric Anholt. Making
assignment_generator::rvalue be ir_dereference instead of ir_rvalue
simplified the code a bit.
Fixes i965 piglit fs-temp-array-mat[234]-index-wr and
vs-varying-array-mat[234]-index-wr.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=34691
Reviewed-by: Eric Anholt <eric at anholt.net>
---
src/glsl/lower_variable_index_to_cond_assign.cpp | 135 +++++++++++++++++++---
1 files changed, 116 insertions(+), 19 deletions(-)
diff --git a/src/glsl/lower_variable_index_to_cond_assign.cpp b/src/glsl/lower_variable_index_to_cond_assign.cpp
index c0b69c8..107bcc6 100644
--- a/src/glsl/lower_variable_index_to_cond_assign.cpp
+++ b/src/glsl/lower_variable_index_to_cond_assign.cpp
@@ -29,6 +29,21 @@
*
* Pre-DX10 GPUs often don't have a native way to do this operation,
* and this works around that.
+ *
+ * The lowering process proceeds as follows. Each non-constant index
+ * found in an r-value is converted to a canonical form \c array[i]. Each
+ * element of the array is conditionally assigned to a temporary by comparing
+ * \c i to a constant index. This is done by cloning the canonical form and
+ * replacing all occurances of \c i with a constant. Each remaining occurance
+ * of the canonical form in the IR is replaced with a dereference of the
+ * temporary variable.
+ *
+ * L-values with non-constant indices are handled similarly. In this case,
+ * the RHS of the assignment is assigned to a temporary. The non-constant
+ * index is replace with the canonical form (just like for r-values). The
+ * temporary is conditionally assigned to each element of the canonical form
+ * by comparing \c i with each index. The same clone-and-replace scheme is
+ * used.
*/
#include "ir.h"
@@ -43,10 +58,70 @@ is_array_or_matrix(const ir_instruction *ir)
return (ir->type->is_array() || ir->type->is_matrix());
}
+/**
+ * Replace a dereference of a variable with a specified r-value
+ *
+ * Each time a dereference of the specified value is replaced, the r-value
+ * tree is cloned.
+ */
+class deref_replacer : public ir_rvalue_visitor {
+public:
+ deref_replacer(const ir_variable *variable_to_replace, ir_rvalue *value)
+ : variable_to_replace(variable_to_replace), value(value),
+ progress(false)
+ {
+ assert(this->variable_to_replace != NULL);
+ assert(this->value != NULL);
+ }
+
+ virtual void handle_rvalue(ir_rvalue **rvalue)
+ {
+ ir_dereference_variable *const dv = (*rvalue)->as_dereference_variable();
+
+ if ((dv != NULL) && (dv->var == this->variable_to_replace)) {
+ this->progress = true;
+ *rvalue = this->value->clone(ralloc_parent(*rvalue), NULL);
+ }
+ }
+
+ const ir_variable *variable_to_replace;
+ ir_rvalue *value;
+ bool progress;
+};
+
+/**
+ * Find a variable index dereference of an array in an rvalue tree
+ */
+class find_variable_index : public ir_hierarchical_visitor {
+public:
+ find_variable_index()
+ : deref(NULL)
+ {
+ /* empty */
+ }
+
+ virtual ir_visitor_status visit_enter(ir_dereference_array *ir)
+ {
+ if (is_array_or_matrix(ir->array)
+ && (ir->array_index->as_constant() == NULL)) {
+ this->deref = ir;
+ return visit_stop;
+ }
+
+ return visit_continue;
+ }
+
+ /**
+ * First array dereference found in the tree that has a non-constant index.
+ */
+ ir_dereference_array *deref;
+};
+
struct assignment_generator
{
ir_instruction* base_ir;
- ir_rvalue* array;
+ ir_dereference *rvalue;
+ ir_variable *old_index;
bool is_write;
unsigned int write_mask;
ir_variable* var;
@@ -61,18 +136,23 @@ struct assignment_generator
* underlying variable.
*/
void *mem_ctx = ralloc_parent(base_ir);
- ir_dereference *element =
- new(mem_ctx) ir_dereference_array(this->array->clone(mem_ctx, NULL),
- new(mem_ctx) ir_constant(i));
- ir_rvalue *variable = new(mem_ctx) ir_dereference_variable(this->var);
- ir_assignment *assignment;
- if (is_write) {
- assignment = new(mem_ctx) ir_assignment(element, variable, condition,
- write_mask);
- } else {
- assignment = new(mem_ctx) ir_assignment(variable, element, condition);
- }
+ /* Clone the old r-value in its entirety. Then replace any occurances of
+ * the old variable index with the new constant index.
+ */
+ ir_dereference *element = this->rvalue->clone(mem_ctx, NULL);
+ ir_constant *const index = new(mem_ctx) ir_constant(i);
+ deref_replacer r(this->old_index, index);
+ element->accept(&r);
+ assert(r.progress);
+
+ /* Generate a conditional assignment to (or from) the constant indexed
+ * array dereference.
+ */
+ ir_rvalue *variable = new(mem_ctx) ir_dereference_variable(this->var);
+ ir_assignment *const assignment = (is_write)
+ ? new(mem_ctx) ir_assignment(element, variable, condition, write_mask)
+ : new(mem_ctx) ir_assignment(variable, element, condition);
list->push_tail(assignment);
}
@@ -274,7 +354,8 @@ public:
}
ir_variable *convert_dereference_array(ir_dereference_array *orig_deref,
- ir_assignment* orig_assign)
+ ir_assignment* orig_assign,
+ ir_dereference *orig_base)
{
assert(is_array_or_matrix(orig_deref->array));
@@ -320,9 +401,12 @@ public:
new(mem_ctx) ir_assignment(lhs, orig_deref->array_index, NULL);
base_ir->insert_before(assign);
+ orig_deref->array_index = lhs->clone(mem_ctx, NULL);
+
assignment_generator ag;
- ag.array = orig_deref->array;
+ ag.rvalue = orig_base;
ag.base_ir = base_ir;
+ ag.old_index = index;
ag.var = var;
if (orig_assign) {
ag.is_write = true;
@@ -342,12 +426,16 @@ public:
virtual void handle_rvalue(ir_rvalue **pir)
{
+ if (this->in_assignee)
+ return;
+
if (!*pir)
return;
ir_dereference_array* orig_deref = (*pir)->as_dereference_array();
if (needs_lowering(orig_deref)) {
- ir_variable* var = convert_dereference_array(orig_deref, 0);
+ ir_variable *var =
+ convert_dereference_array(orig_deref, NULL, orig_deref);
assert(var);
*pir = new(ralloc_parent(base_ir)) ir_dereference_variable(var);
this->progress = true;
@@ -359,10 +447,11 @@ public:
{
ir_rvalue_visitor::visit_leave(ir);
- ir_dereference_array *orig_deref = ir->lhs->as_dereference_array();
+ find_variable_index f;
+ ir->lhs->accept(&f);
- if (needs_lowering(orig_deref)) {
- convert_dereference_array(orig_deref, ir);
+ if ((f.deref != NULL) && storage_type_needs_lowering(f.deref)) {
+ convert_dereference_array(f.deref, ir, ir->lhs);
ir->remove();
this->progress = true;
}
@@ -383,7 +472,15 @@ lower_variable_index_to_cond_assign(exec_list *instructions,
lower_temp,
lower_uniform);
- visit_list_elements(&v, instructions);
+ /* Continue lowering until no progress is made. If there are multiple
+ * levels of indirection (e.g., non-constant indexing of array elements and
+ * matrix columns of an array of matrix), each pass will only lower one
+ * level of indirection.
+ */
+ do {
+ v.progress = false;
+ visit_list_elements(&v, instructions);
+ } while (v.progress);
return v.progress;
}
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