[Mesa-dev] [PATCH 21/23] glsl: Recognize double negated multiplies and divides as equal

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

For example (-x * 43) and (x * -43) should be considered common.

No shader-db changes.  I'll probably drop this patch, but I wanted to
send it out to show that I tried this too.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/glsl/ir_equals.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/glsl/ir_equals.cpp b/src/glsl/ir_equals.cpp
index 5f5af5b..664cbfa 100644
--- a/src/glsl/ir_equals.cpp
+++ b/src/glsl/ir_equals.cpp
@@ -218,6 +218,16 @@ ir_expression::equals(const ir_instruction *ir, enum ir_node_type ignore) const
    if (operation != other->operation)
       return false;
 
+   if (operation == ir_binop_mul || operation == ir_binop_div) {
+      /* For multiplication and division we want an even-parity of negations on
+       * operands.  This means that 'x * y' equals '-x * -y'.
+       */
+      return ((operands[0]->equals(other->operands[0], ignore) &&
+               operands[1]->equals(other->operands[1], ignore)) ||
+              (operands[0]->negative_equals(other->operands[0], ignore) &&
+               operands[1]->negative_equals(other->operands[1], ignore)));
+   }
+
    for (unsigned i = 0; i < get_num_operands(); i++) {
       if (!operands[i]->equals(other->operands[i], ignore))
          return false;
-- 
2.1.0