nir: Differentiate between signed and unsigned versions of find_msb

We also make the return types match GLSL.  The GLSL spec specifies that
findMSB and findLSB return a signed integer.  Previously, nir had them
return unsigned.  This updates nir's behavior to match what GLSL expects.

We also update the nir-to-fs generator to take the new instructions.  While
we're at it, we fix the case where the input to findMSB is zero.

Reviewed-by: Connor Abbott <[email protected]>

1 files changed, 19 insertions, 3 deletions

diff --git a/src/glsl/nir/glsl_to_nir.cpp b/src/glsl/nir/glsl_to_nir.cpp
index 40cb2448cf8..58721913f74 100644
--- a/src/glsl/nir/glsl_to_nir.cpp
+++ b/src/glsl/nir/glsl_to_nir.cpp
@@ -1123,9 +1123,25 @@ nir_visitor::visit(ir_expression *ir)
    case ir_unop_bitfield_reverse:
       emit(nir_op_bitfield_reverse, dest_size, srcs);
       break;
-   case ir_unop_bit_count: emit(nir_op_bit_count, dest_size, srcs); break;
-   case ir_unop_find_msb:  emit(nir_op_find_msb,  dest_size, srcs); break;
-   case ir_unop_find_lsb:  emit(nir_op_find_lsb,  dest_size, srcs); break;
+   case ir_unop_bit_count:
+      emit(nir_op_bit_count, dest_size, srcs);
+      break;
+   case ir_unop_find_msb:
+      switch (types[0]) {
+      case GLSL_TYPE_UINT:
+         emit(nir_op_ufind_msb, dest_size, srcs);
+         break;
+      case GLSL_TYPE_INT:
+         emit(nir_op_ifind_msb, dest_size, srcs);
+         break;
+      default:
+         unreachable("Invalid type for findMSB()");
+      }
+      break;
+   case ir_unop_find_lsb:
+      emit(nir_op_find_lsb,  dest_size, srcs);
+      break;
+
    case ir_unop_noise:
       switch (ir->type->vector_elements) {
       case 1: