Mesa (staging/18.1): i965/fs: Properly handle sign(-abs(x))

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Module: Mesa
Branch: staging/18.1
Commit: e7d4549ac039f93e90b707b6f50cb9a80bbd8789
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=e7d4549ac039f93e90b707b6f50cb9a80bbd8789

Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Tue Jun 26 15:11:21 2018 -0700

i965/fs: Properly handle sign(-abs(x))

Fixes new piglit tests:

 - glsl-1.10/execution/fs-sign-neg-abs.shader_test
 - glsl-1.10/execution/fs-sign-sat-neg-abs.shader_test
 - glsl-1.10/execution/vs-sign-neg-abs.shader_test
 - glsl-1.10/execution/vs-sign-sat-neg-abs.shader_test

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Cc: mesa-stable at lists.freedesktop.org
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com>
(cherry picked from commit 88bd37c01060169b451ca2c3900830342d34a9a2)

---

 src/intel/compiler/brw_fs_nir.cpp | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/intel/compiler/brw_fs_nir.cpp b/src/intel/compiler/brw_fs_nir.cpp
index 47e26f8ec4..8eb69b9a38 100644
--- a/src/intel/compiler/brw_fs_nir.cpp
+++ b/src/intel/compiler/brw_fs_nir.cpp
@@ -821,11 +821,20 @@ fs_visitor::nir_emit_alu(const fs_builder &bld, nir_alu_instr *instr)
 
    case nir_op_fsign: {
       if (op[0].abs) {
-         /* Straightforward since the source can be assumed to be
-          * non-negative.
+         /* Straightforward since the source can be assumed to be either
+          * strictly >= 0 or strictly <= 0 depending on the setting of the
+          * negate flag.
           */
          set_condmod(BRW_CONDITIONAL_NZ, bld.MOV(result, op[0]));
-         set_predicate(BRW_PREDICATE_NORMAL, bld.MOV(result, brw_imm_f(1.0f)));
+
+         inst = (op[0].negate)
+            ? bld.MOV(result, brw_imm_f(-1.0f))
+            : bld.MOV(result, brw_imm_f(1.0f));
+
+         set_predicate(BRW_PREDICATE_NORMAL, inst);
+
+         if (instr->dest.saturate)
+            inst->saturate = true;
 
       } else if (type_sz(op[0].type) < 8) {
          /* AND(val, 0x80000000) gives the sign bit.