Mesa (master): glsl: Avoid extra if statements for logic and/ or with no side effects.

[Eric Anholt]

Module: Mesa
Branch: master
Commit: ead3589aa2810b66164178a1d55d2063cfa3b041
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=ead3589aa2810b66164178a1d55d2063cfa3b041

Author: Eric Anholt <eric at anholt.net>
Date:   Tue Feb  7 22:59:24 2012 -0800

glsl: Avoid extra if statements for logic and/or with no side effects.

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.  Reduces
i965 instructions generated in unigine tropics and sanctuary,
yofrankie, warsow, gstreamer shaders, and the weston compositor.

shader-db results:
Total instructions: 213052 -> 212752
38/1246 programs affected (3.0%)
14309 -> 14009 instructions in affected programs (2.1% reduction)

---

 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",