[Mesa-dev] [PATCH] glsl: Avoid extra if statements for logic and/or with no side effects.

[Eric Anholt]

This avoids extra if statements in the common case of just comparing
two expressions that don't involve assignments or function calls,
along with simplifying the handling of constant expressions.  Since GL
3.0 availability, my actual application testcases for improvement from
this patch have apparently gone away, but it still seems like the
right thing to do.

Reveals a bug in piglit's glsl-algebraic-logicor-true.
---
 src/glsl/ast_to_hir.cpp |   23 ++++++-----------------
 1 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp
index c580359..75d7e9d 100644
--- a/src/glsl/ast_to_hir.cpp
+++ b/src/glsl/ast_to_hir.cpp
@@ -1199,15 +1199,9 @@ ast_expression::hir(exec_list *instructions,
       op[1] = get_scalar_boolean_operand(&rhs_instructions, state, this, 1,
 					 "RHS", &error_emitted);
 
-      ir_constant *op0_const = op[0]->constant_expression_value();
-      if (op0_const) {
-	 if (op0_const->value.b[0]) {
-	    instructions->append_list(&rhs_instructions);
-	    result = op[1];
-	 } else {
-	    result = op0_const;
-	 }
-	 type = glsl_type::bool_type;
+      if (rhs_instructions.is_empty()) {
+	 result = new(ctx) ir_expression(ir_binop_logic_and, op[0], op[1]);
+	 type = result->type;
       } else {
 	 ir_variable *const tmp = new(ctx) ir_variable(glsl_type::bool_type,
 						       "and_tmp",
@@ -1241,14 +1235,9 @@ ast_expression::hir(exec_list *instructions,
       op[1] = get_scalar_boolean_operand(&rhs_instructions, state, this, 1,
 					 "RHS", &error_emitted);
 
-      ir_constant *op0_const = op[0]->constant_expression_value();
-      if (op0_const) {
-	 if (op0_const->value.b[0]) {
-	    result = op0_const;
-	 } else {
-	    result = op[1];
-	 }
-	 type = glsl_type::bool_type;
+      if (rhs_instructions.is_empty()) {
+	 result = new(ctx) ir_expression(ir_binop_logic_or, op[0], op[1]);
+	 type = result->type;
       } else {
 	 ir_variable *const tmp = new(ctx) ir_variable(glsl_type::bool_type,
 						       "or_tmp",
-- 
1.7.9