[Mesa-dev] [PATCH 4/8] i965/fs: Fix nir_op_fsign of absolute value.

[Francisco Jerez]

This does point at the front-end emitting silly code that could have
been optimized out, but the current fsign implementation would emit
bogus IR if abs was set for the argument (because it would apply the
abs modifier on an unsigned integer type), and we shouldn't rely on
the upper layer's optimization passes for correctness.
---
 src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index e1ab598..e0c2fa0 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -701,7 +701,14 @@ fs_visitor::nir_emit_alu(const fs_builder &bld, nir_alu_instr *instr)
       break;
 
    case nir_op_fsign: {
-      if (type_sz(op[0].type) < 8) {
+      if (op[0].abs) {
+         /* Straightforward since the source can be assumed to be
+          * non-negative.
+          */
+         set_condmod(BRW_CONDITIONAL_NZ, bld.MOV(result, op[0]));
+         set_predicate(BRW_PREDICATE_NORMAL, bld.MOV(result, brw_imm_f(1.0f)));
+
+      } else if (type_sz(op[0].type) < 8) {
          /* AND(val, 0x80000000) gives the sign bit.
           *
           * Predicated OR ORs 1.0 (0x3f800000) with the sign bit if val is not
-- 
2.10.2