Add DW_OP_LLVM_select_bit_piece DWARF operation

Second more complex DWARF expression operation, that is usefull for
SIMD/SIMT like architectures is DW_OP_LLVM_select_bit_piece. This
operation pops three stack entries, where the first must be an integral
type value that represents a bit mask, the second must be a location
description that represents the one-location description and the third
must be a location description that represents the zero-location
description.

Resulting composite location description contains a given number of
pieces of a given bit size, created with parts from either of the two
location description, based on the bit mask.

gdb/ChangeLog:

        * compile/compile-loc2c.c (compute_stack_depth_worker): Add
        new DW_OP_LLVM_select_bit_piece operation support.
        * dwarf2/expr.c (dwarf_expr_context::create_select_composite):
        New method that creates the select bit piece composite.
        (dwarf_location::slice): New method.
        (dwarf_composite::slice): New method.
        (dwarf_expr_context::execute_stack_op): Add new
        DW_OP_LLVM_select_bit_piece operation support.
        * dwarf2/loc.c (dwarf2_get_symbol_read_needs): Add new
        DW_OP_LLVM_select_bit_piece operation support.
        (disassemble_dwarf_expression): Add new
        DW_OP_LLVM_select_bit_piece operation support.

include/ChangeLog:

        * dwarf2.def: Add new DW_OP_LLVM_select_bit_piece enumeration.

gdb/testsuite/ChangeLog:

        * gdb.dwarf2/dw2-llvm-select-bit-piece.exp: New test.
        * lib/dwarf.exp: Add new DW_OP_LLVM_select_bit_piece operation
        support.

6 files changed, 320 insertions, 0 deletions

diff --git a/gdb/compile/compile-loc2c.c b/gdb/compile/compile-loc2c.c
index 26a4def312c..83863276b4c 100644
--- a/gdb/compile/compile-loc2c.c
+++ b/gdb/compile/compile-loc2c.c
@@ -366,6 +366,10 @@ compute_stack_depth_worker (int start, int *need_tempvar,
 	  ++stack_depth;
 	  break;
 
+	case DW_OP_LLVM_select_bit_piece:
+	  stack_depth -= 2;
+	  break;
+
 	case DW_OP_LLVM_extend:
 	case DW_OP_LLVM_piece_end:
 	case DW_OP_LLVM_offset_constu:
diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index f8c23a7842d..3ae1a6289dd 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -461,6 +461,15 @@ public:
     ill_formed_expression ();
   }
 
+  /* Make a slice of a location description with an added bit offset
+     BIT_OFFSET and BIT_SIZE size in bits.
+
+     In the case of a composite location description, function returns
+     a minimum subset of that location description that starts on a
+     given offset of a given size.  */
+  virtual std::unique_ptr<dwarf_location> slice (LONGEST bit_offset,
+						 LONGEST bit_size) const;
+
   /* Read contents from the described location.
 
      The read operation is performed in the context of a FRAME.
@@ -616,6 +625,17 @@ protected:
 
 using dwarf_location_up = std::unique_ptr<dwarf_location>;
 
+/* This is a default implementation used for
+   non-composite location descriptions.  */
+
+std::unique_ptr<dwarf_location>
+dwarf_location::slice (LONGEST bit_offset, LONGEST bit_size) const
+{
+  dwarf_location_up location_slice = this->clone_location ();
+  location_slice->add_bit_offset (bit_offset);
+  return location_slice;
+}
+
 void
 dwarf_location::read_from_gdb_value (frame_info *frame, struct value *value,
 				     int value_bit_offset,
@@ -1573,6 +1593,9 @@ public:
     return make_unique<dwarf_composite> (*this);
   }
 
+  std::unique_ptr<dwarf_location> slice (LONGEST bit_offset,
+					 LONGEST bit_size) const override;
+
   void add_piece (std::unique_ptr<dwarf_location> location, ULONGEST bit_size)
   {
     gdb_assert (location != nullptr);
@@ -1659,6 +1682,64 @@ private:
   bool m_completed = false;
 };
 
+std::unique_ptr<dwarf_location>
+dwarf_composite::slice (LONGEST bit_offset, LONGEST bit_size) const
+{
+  /* Size 0 is never expected at this point.  */
+  gdb_assert (bit_size != 0);
+
+  unsigned int pieces_num = m_pieces.size ();
+  LONGEST total_bit_size = bit_size;
+  LONGEST total_bits_to_skip = m_offset * HOST_CHAR_BIT
+			       + m_bit_suboffset + bit_offset;
+  std::vector<piece> piece_slices;
+  unsigned int i;
+
+  for (i = 0; i < pieces_num; i++)
+    {
+      LONGEST piece_bit_size = m_pieces[i].size;
+
+      if (total_bits_to_skip < piece_bit_size)
+	break;
+
+      total_bits_to_skip -= piece_bit_size;
+    }
+
+  for (; i < pieces_num; i++)
+    {
+      if (total_bit_size == 0)
+	break;
+
+      gdb_assert (total_bit_size > 0);
+      LONGEST slice_bit_size = m_pieces[i].size - total_bits_to_skip;
+
+      if (total_bit_size < slice_bit_size)
+	slice_bit_size = total_bit_size;
+
+      std::unique_ptr<dwarf_location> slice
+	= m_pieces[i].location->slice (total_bits_to_skip, slice_bit_size);
+      piece_slices.emplace_back (std::move (slice), slice_bit_size);
+
+      total_bit_size -= slice_bit_size;
+      total_bits_to_skip = 0;
+    }
+
+  unsigned int slices_num = piece_slices.size ();
+
+  /* Only one piece found, so there is no reason to
+      make a composite location description.  */
+  if (slices_num == 1)
+    return std::move (piece_slices[0].location);
+
+  std::unique_ptr<dwarf_composite> composite_slice
+    = make_unique<dwarf_composite> (m_arch, m_per_cu);
+
+  for (piece &piece : piece_slices)
+    composite_slice->add_piece (std::move (piece.location), piece.size);
+
+  return composite_slice;
+}
+
 void
 dwarf_composite::read (frame_info *frame, gdb_byte *buf,
 		       int buf_bit_offset, size_t bit_size,
@@ -2534,6 +2615,20 @@ private:
   void create_extend_composite (ULONGEST piece_bit_size,
 				ULONGEST pieces_count);
 
+  /* It pops three stack entries.  The first must be an integral type
+     value that represents a bit mask.  The second must be a location
+     description that represents the one-location description.  The
+     third must be a location description that represents the
+     zero-location description.
+
+     A complete composite location description created with parts from
+     either of the two location description, based on the bit mask,
+     is pushed on top of the DWARF stack.  PIECE_BIT_SIZE represent
+     a size in bits of each piece and PIECES_COUNT represents a number
+     of pieces required.  */
+  void create_select_composite (ULONGEST piece_bit_size,
+				ULONGEST pieces_count);
+
   /* The engine for the expression evaluator.  Using the context in this
      object, evaluate the expression between OP_PTR and OP_END.  */
   void execute_stack_op (const gdb_byte *op_ptr, const gdb_byte *op_end);
@@ -2921,6 +3016,60 @@ dwarf_expr_context::create_extend_composite (ULONGEST piece_bit_size,
 }
 
 void
+dwarf_expr_context::create_select_composite (ULONGEST piece_bit_size,
+					     ULONGEST pieces_count)
+{
+  gdb::byte_vector mask_buf;
+  gdbarch *arch = this->m_per_objfile->objfile->arch ();
+
+  if (stack_empty_p () || piece_bit_size == 0 || pieces_count == 0)
+    ill_formed_expression ();
+
+  dwarf_value_up mask = to_value (pop (), address_type ());
+
+  type *mask_type = mask->type ();
+  ULONGEST mask_size = TYPE_LENGTH (mask_type);
+  dwarf_require_integral (mask_type);
+
+  if (mask_size * HOST_CHAR_BIT < pieces_count)
+    ill_formed_expression ();
+
+  mask_buf.resize (mask_size);
+
+  copy_bitwise (mask_buf.data (), 0, mask->contents ().data (),
+		0, mask_size * HOST_CHAR_BIT,
+		type_byte_order (mask_type) == BFD_ENDIAN_BIG);
+
+  if (stack_empty_p ())
+    ill_formed_expression ();
+
+  dwarf_location_up one = to_location (pop (), arch);
+
+  if (stack_empty_p ())
+    ill_formed_expression ();
+
+  dwarf_location_up zero = to_location (pop (), arch);
+
+  std::unique_ptr<dwarf_composite> composite
+    = make_unique<dwarf_composite> (arch, this->m_per_cu);
+
+  for (ULONGEST i = 0; i < pieces_count; i++)
+    {
+      std::unique_ptr<dwarf_location> slice;
+
+      if ((mask_buf.data ()[i / HOST_CHAR_BIT] >> (i % HOST_CHAR_BIT)) & 1)
+	slice = one->slice (i * piece_bit_size, piece_bit_size);
+      else
+	slice = zero->slice (i * piece_bit_size, piece_bit_size);
+
+      composite->add_piece (std::move (slice), piece_bit_size);
+    }
+
+  composite->set_completed (true);
+  push (std::move (composite));
+}
+
+void
 dwarf_expr_context::eval (const gdb_byte *addr, size_t len)
 {
   int old_recursion_depth = this->m_recursion_depth;
@@ -4161,6 +4310,17 @@ dwarf_expr_context::execute_stack_op (const gdb_byte *op_ptr,
 	    break;
 	  }
 
+	case DW_OP_LLVM_select_bit_piece:
+	  {
+	    uint64_t piece_bit_size, pieces_count;
+
+	    /* Record the piece.  */
+	    op_ptr = safe_read_uleb128 (op_ptr, op_end, &piece_bit_size);
+	    op_ptr = safe_read_uleb128 (op_ptr, op_end, &pieces_count);
+	    create_select_composite (piece_bit_size, pieces_count);
+	    break;
+	  }
+
 	default:
 	  error (_("Unhandled dwarf expression opcode 0x%x"), op);
 	}
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index d8bcd542776..071baad76d1 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -1955,6 +1955,7 @@ dwarf2_get_symbol_read_needs (gdb::array_view<const gdb_byte> expr,
 
 	case DW_OP_bit_piece:
 	case DW_OP_LLVM_extend:
+	case DW_OP_LLVM_select_bit_piece:
 	  op_ptr = safe_skip_leb128 (op_ptr, expr_end);
 	  op_ptr = safe_skip_leb128 (op_ptr, expr_end);
 	  break;
@@ -3679,6 +3680,17 @@ disassemble_dwarf_expression (struct ui_file *stream,
 	                      pulongest (ul), pulongest (count));
 	  }
 	  break;
+
+	case DW_OP_LLVM_select_bit_piece:
+	  {
+	    uint64_t count;
+
+	    data = safe_read_uleb128 (data, end, &ul);
+	    data = safe_read_uleb128 (data, end, &count);
+	    fprintf_filtered (stream, " piece size %s (bits) pieces count %s",
+			      pulongest (ul), pulongest (count));
+	  }
+	  break;
 	}
 
       fprintf_filtered (stream, "\n");
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-llvm-select-bit-piece.exp b/gdb/testsuite/gdb.dwarf2/dw2-llvm-select-bit-piece.exp
new file mode 100644
index 00000000000..c5ed6efbd75
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/dw2-llvm-select-bit-piece.exp
@@ -0,0 +1,138 @@
+# Copyright (C) 2017-2021 Free Software Foundation, Inc.
+# Copyright (C) 2020-2021 Advanced Micro Devices, Inc. All rights reserved.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test the new DW_OP_LLVM_select_bit_piece operation.
+#
+# The test uses a composite location description, where all the pieces
+# are selected from two registers in odd/even pattern using the new
+# operation.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+}
+
+# Choose suitable integer registers for the test.
+
+set dwarf_regnum {0 1}
+
+if { [is_aarch64_target] } {
+    set regname {x0 x1}
+} elseif { [is_aarch32_target]
+	   || [istarget "s390*-*-*" ]
+	   || [istarget "powerpc*-*-*"]
+	   || [istarget "rs6000*-*-aix*"] } {
+    set regname {r0 r1}
+} elseif { [is_x86_like_target] } {
+    set regname {eax ecx}
+} elseif { [is_amd64_regs_target] } {
+    set regname {rax rdx}
+} else {
+    verbose "Skipping $gdb_test_file_name."
+    return
+}
+
+standard_testfile var-access.c ${gdb_test_file_name}-dw.S
+
+# Make some DWARF for the test.
+
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+    global dwarf_regnum regname srcdir subdir srcfile
+    set buf_src [gdb_target_symbol buf]
+
+    set main_result [function_range main ${srcdir}/${subdir}/${srcfile}]
+    set main_start [lindex $main_result 0]
+    set main_length [lindex $main_result 1]
+
+    cu {} {
+	DW_TAG_compile_unit {
+	    {DW_AT_name var-access.c}
+	    {DW_AT_comp_dir /tmp}
+	} {
+	    declare_labels int_type_label char_type_label array_type_label
+
+	    # define char type
+	    char_type_label: DW_TAG_base_type {
+		{DW_AT_name "char"}
+		{DW_AT_encoding @DW_ATE_signed}
+		{DW_AT_byte_size 1 DW_FORM_sdata}
+	    }
+
+	    int_type_label: DW_TAG_base_type {
+		{DW_AT_name "int"}
+		{DW_AT_encoding @DW_ATE_signed}
+		{DW_AT_byte_size 4 DW_FORM_sdata}
+	    }
+
+	    array_type_label: DW_TAG_array_type {
+		{DW_AT_type :$char_type_label}
+	    } {
+		DW_TAG_subrange_type {
+		    {DW_AT_type :$int_type_label}
+		    {DW_AT_upper_bound 7 DW_FORM_udata}
+		}
+	    }
+
+	    DW_TAG_subprogram {
+		{DW_AT_name main}
+		{DW_AT_low_pc $main_start addr}
+		{DW_AT_high_pc $main_length data8}
+	    } {
+
+		# Odd array elements are in first byte of REGNAME 0 register,
+		# while even elements are in first byte of REGNAME 1 register.
+		DW_TAG_variable {
+		    {DW_AT_name var_array}
+		    {DW_AT_type :$array_type_label}
+		    {DW_AT_location {
+			DW_OP_regx [lindex $dwarf_regnum 0]
+			DW_OP_LLVM_extend 8 8
+                        DW_OP_regx [lindex $dwarf_regnum 1]
+			DW_OP_LLVM_extend 8 8
+			DW_OP_constu 0xaa
+			DW_OP_LLVM_select_bit_piece 8 8
+		    } SPECIAL_expr}
+		}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} \
+     [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_test_no_output "set var \$[lindex $regname 0] = 0x04030201" "init reg 0"
+gdb_test_no_output "set var \$[lindex $regname 1] = 0x01020304" "init reg 1"
+
+# Determine byte order.
+set endian [get_endianness]
+
+switch $endian {
+	little {set val "0x1, 0x4, 0x1, 0x4, 0x1, 0x4, 0x1, 0x4"}
+	big {set val "0x4, 0x1, 0x4, 0x1, 0x4, 0x1, 0x4, 0x1"}
+}
+
+gdb_test "print/x var_array" " = \\{${val}\\}" "var_array print"
+
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index d2f3445c926..3bb9bdbd3d4 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -1230,6 +1230,11 @@ namespace eval Dwarf {
 		    _op .uleb128 [lindex $line 2]
 		}
 
+		DW_OP_LLVM_select_bit_piece {
+		    _op .uleb128 [lindex $line 1]
+		    _op .uleb128 [lindex $line 2]
+		}
+
 		default {
 		    if {[llength $line] > 1} {
 			error "Unimplemented: operands in location for $opcode"
diff --git a/include/dwarf2.def b/include/dwarf2.def
index 3d1d831d0fb..abc1125df2c 100644
--- a/include/dwarf2.def
+++ b/include/dwarf2.def
@@ -711,6 +711,7 @@ DW_OP_DUP (DW_OP_LLVM_bit_offset, 0xe5)
 DW_OP (DW_OP_LLVM_undefined, 0xe7)
 DW_OP_DUP (DW_OP_LLVM_piece_end, 0xea)
 DW_OP (DW_OP_LLVM_extend, 0xeb)
+DW_OP (DW_OP_LLVM_select_bit_piece, 0xec)
 DW_END_OP
 
 DW_FIRST_ATE (DW_ATE_void, 0x0)