[Mesa-dev] [PATCH 2/2] i965/fs: Don't double-accept operands of logical and/or/xor operations.

[Kenneth Graunke]

emit_bool_to_cond_code() takes separate paths for ir_expressions and.

If the argument to emit_bool_to_cond_code() is an ir_expression, we
loop over the operands, calling accept() on each of them, which
generates assembly code to compute that subexpression.  We then emit
one or two final instruction that perform the top-level operation on
those operands.

If it's not an expression (say, a boolean-valued variable), we simply
call accept() on the whole value.

In commit 80ecb8f1 (i965/fs: Avoid generating extra AND instructions on
bool logic ops), Eric made logic operations jump out of the expression
path to the non-expression path.

Unfortunately, this meant that we would first accept() the two operands,
skip generating any code that used them, then accept() the whole
expression, generating code for the operands a second time.

Dead code elimination would always remove the first set of redundant
operand assembly, since nothing actually used them.  But we shouldn't
generate it in the first place.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
Cc: Matt Turner <mattst88 at gmail.com>
Cc: Eric Anholt <eric at anholt.net>
---
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 946525b..bd94ea3 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -1724,7 +1724,10 @@ fs_visitor::emit_bool_to_cond_code(ir_rvalue *ir)
 {
    ir_expression *expr = ir->as_expression();
 
-   if (expr) {
+   if (expr &&
+       expr->operation != ir_binop_logic_and &&
+       expr->operation != ir_binop_logic_or &&
+       expr->operation != ir_binop_logic_xor) {
       fs_reg op[2];
       fs_inst *inst;
 
@@ -1742,11 +1745,6 @@ fs_visitor::emit_bool_to_cond_code(ir_rvalue *ir)
 	 inst->conditional_mod = BRW_CONDITIONAL_Z;
 	 break;
 
-      case ir_binop_logic_xor:
-      case ir_binop_logic_or:
-      case ir_binop_logic_and:
-	 goto out;
-
       case ir_unop_f2b:
 	 if (brw->gen >= 6) {
 	    emit(CMP(reg_null_d, op[0], fs_reg(0.0f), BRW_CONDITIONAL_NZ));
@@ -1788,7 +1786,6 @@ fs_visitor::emit_bool_to_cond_code(ir_rvalue *ir)
       return;
    }
 
-out:
    ir->accept(this);
 
    fs_inst *inst = emit(AND(reg_null_d, this->result, fs_reg(1)));
-- 
1.8.3.4