Mesa (master): nir/lower_bit_size: fix lowering of shifts

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Module: Mesa
Branch: master
Commit: 715ef95700c06a09582744f3d873107728615b7f
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=715ef95700c06a09582744f3d873107728615b7f

Author: Rhys Perry <pendingchaos02 at gmail.com>
Date:   Tue Mar 31 13:51:32 2020 +0100

nir/lower_bit_size: fix lowering of shifts

Signed-off-by: Rhys Perry <pendingchaos02 at gmail.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4387>

---

 src/compiler/nir/nir_lower_bit_size.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/compiler/nir/nir_lower_bit_size.c b/src/compiler/nir/nir_lower_bit_size.c
index 531e6aa5289..3ba63c81adc 100644
--- a/src/compiler/nir/nir_lower_bit_size.c
+++ b/src/compiler/nir/nir_lower_bit_size.c
@@ -48,6 +48,7 @@ static void
 lower_instr(nir_builder *bld, nir_alu_instr *alu, unsigned bit_size)
 {
    const nir_op op = alu->op;
+   unsigned dst_bit_size = alu->dest.dest.ssa.bit_size;
 
    bld->cursor = nir_before_instr(&alu->instr);
 
@@ -58,9 +59,14 @@ lower_instr(nir_builder *bld, nir_alu_instr *alu, unsigned bit_size)
 
       nir_alu_type type = nir_op_infos[op].input_types[i];
       if (nir_alu_type_get_type_size(type) == 0)
-         srcs[i] = convert_to_bit_size(bld, src, type, bit_size);
-      else
-         srcs[i] = src;
+         src = convert_to_bit_size(bld, src, type, bit_size);
+
+      if (i == 1 && (op == nir_op_ishl || op == nir_op_ishr || op == nir_op_ushr)) {
+         assert(util_is_power_of_two_nonzero(dst_bit_size));
+         src = nir_iand(bld, src, nir_imm_int(bld, dst_bit_size - 1));
+      }
+
+      srcs[i] = src;
    }
 
    /* Emit the lowered ALU instruction */
@@ -68,7 +74,6 @@ lower_instr(nir_builder *bld, nir_alu_instr *alu, unsigned bit_size)
       nir_build_alu(bld, op, srcs[0], srcs[1], srcs[2], srcs[3]);
 
    /* Convert result back to the original bit-size */
-   unsigned dst_bit_size = alu->dest.dest.ssa.bit_size;
    nir_alu_type type = nir_op_infos[op].output_type;
    nir_ssa_def *dst = convert_to_bit_size(bld, lowered_dst, type, dst_bit_size);
    nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(dst));