glsl: Rewrite and fix min/max to saturate optimization.

There were some bugs, and the code was really difficult to follow. We
would optimize

   min(max(x, b), 1.0) into max(sat(x), b)

but not pay attention to the order of min/max and also do

   max(min(x, b), 1.0) into max(sat(x), b)

Corrects four shaders from Champions of Regnum that do

   min(max(x, 1), 10)

and corrects rendering of Mass Effect under VMware Workstation.

Cc: "10.4 10.5" <[email protected]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89180
Reviewed-by: Abdiel Janulgue <[email protected]>
Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 46 insertions, 29 deletions

diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index 6784242ff5d..c3f3842bab3 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -744,48 +744,65 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
        * a saturate operation
        */
       for (int op = 0; op < 2; op++) {
-         ir_expression *minmax = op_expr[op];
+         ir_expression *inner_expr = op_expr[op];
          ir_constant *outer_const = op_const[1 - op];
          ir_expression_operation op_cond = (ir->operation == ir_binop_max) ?
             ir_binop_min : ir_binop_max;
 
-         if (!minmax || !outer_const || (minmax->operation != op_cond))
+         if (!inner_expr || !outer_const || (inner_expr->operation != op_cond))
             continue;
 
+         /* One of these has to be a constant */
+         if (!inner_expr->operands[0]->as_constant() &&
+             !inner_expr->operands[1]->as_constant())
+            break;
+
          /* Found a min(max) combination. Now try to see if its operands
           * meet our conditions that we can do just a single saturate operation
           */
          for (int minmax_op = 0; minmax_op < 2; minmax_op++) {
-            ir_rvalue *inner_val_a = minmax->operands[minmax_op];
-            ir_rvalue *inner_val_b = minmax->operands[1 - minmax_op];
+            ir_rvalue *x = inner_expr->operands[minmax_op];
+            ir_rvalue *y = inner_expr->operands[1 - minmax_op];
 
-            if (!inner_val_a || !inner_val_b)
+            ir_constant *inner_const = y->as_constant();
+            if (!inner_const)
                continue;
 
-            /* Found a {min|max} ({max|min} (x, 0.0), 1.0) operation and its variations */
-            if ((outer_const->is_one() && inner_val_a->is_zero()) ||
-                (inner_val_a->is_one() && outer_const->is_zero()))
-               return saturate(inner_val_b);
-
-            /* Found a {min|max} ({max|min} (x, 0.0), b) where b < 1.0
-             * and its variations
-             */
-            if (is_less_than_one(outer_const) && inner_val_b->is_zero())
-               return expr(ir_binop_min, saturate(inner_val_a), outer_const);
-
-            if (!inner_val_b->as_constant())
-               continue;
-
-            if (is_less_than_one(inner_val_b->as_constant()) && outer_const->is_zero())
-               return expr(ir_binop_min, saturate(inner_val_a), inner_val_b);
-
-            /* Found a {min|max} ({max|min} (x, b), 1.0), where b > 0.0
-             * and its variations
-             */
-            if (outer_const->is_one() && is_greater_than_zero(inner_val_b->as_constant()))
-               return expr(ir_binop_max, saturate(inner_val_a), inner_val_b);
-            if (inner_val_b->as_constant()->is_one() && is_greater_than_zero(outer_const))
-               return expr(ir_binop_max, saturate(inner_val_a), outer_const);
+            /* min(max(x, 0.0), 1.0) is sat(x) */
+            if (ir->operation == ir_binop_min &&
+                inner_const->is_zero() &&
+                outer_const->is_one())
+               return saturate(x);
+
+            /* max(min(x, 1.0), 0.0) is sat(x) */
+            if (ir->operation == ir_binop_max &&
+                inner_const->is_one() &&
+                outer_const->is_zero())
+               return saturate(x);
+
+            /* min(max(x, 0.0), b) where b < 1.0 is sat(min(x, b)) */
+            if (ir->operation == ir_binop_min &&
+                inner_const->is_zero() &&
+                is_less_than_one(outer_const))
+               return saturate(expr(ir_binop_min, x, outer_const));
+
+            /* max(min(x, b), 0.0) where b < 1.0 is sat(min(x, b)) */
+            if (ir->operation == ir_binop_max &&
+                is_less_than_one(inner_const) &&
+                outer_const->is_zero())
+               return saturate(expr(ir_binop_min, x, inner_const));
+
+            /* max(min(x, 1.0), b) where b > 0.0 is sat(max(x, b)) */
+            if (ir->operation == ir_binop_max &&
+                inner_const->is_one() &&
+                is_greater_than_zero(outer_const))
+               return saturate(expr(ir_binop_max, x, outer_const));
+
+            /* min(max(x, b), 1.0) where b > 0.0 is sat(max(x, b)) */
+            if (ir->operation == ir_binop_min &&
+                is_greater_than_zero(inner_const) &&
+                outer_const->is_one())
+               return saturate(expr(ir_binop_max, x, inner_const));
          }
       }