Reuse buffers across gdb_pretty_print_insn calls

gdb_pretty_print_insn allocates and destroys a couple local buffers
each time it is called, which can be many times when disassembling a
region of memory.  Avoid that overhead by adding a new class that
holds the buffers and making gdb_pretty_print_insn a method of that
class, so that the buffers can be reused across calls.

gdb/ChangeLog:
2017-02-02  Pedro Alves  <palves@redhat.com>

	* disasm.c (gdb_pretty_print_insn): Rename to ...
	(gdb_pretty_print_disassembler::pretty_print_insn): ... this.
	Remove gdbarch parameter.  Adapt to clear the object's buffers
	instead of allocating new buffers, and to print using the object's
	gdb_disassembler instead of calling gdb_print_insn.
	(dump_insns): Use gdb_pretty_print_disassembler.
	* disasm.h (gdb_pretty_print_insn): Delete declaration.
	(gdb_pretty_print_disassembler): New class.
	* record-btrace.c (btrace_insn_history): Use
	gdb_pretty_print_disassembler.

1 files changed, 27 insertions, 4 deletions

diff --git a/gdb/disasm.h b/gdb/disasm.h
index dcc01e1..385cae6 100644
--- a/gdb/disasm.h
+++ b/gdb/disasm.h
@@ -97,11 +97,34 @@ extern void gdb_disassembly (struct gdbarch *gdbarch, struct ui_out *uiout,
 extern int gdb_print_insn (struct gdbarch *gdbarch, CORE_ADDR memaddr,
 			   struct ui_file *stream, int *branch_delay_insns);
 
-/* Prints the instruction INSN into UIOUT and returns the length of
-   the printed instruction in bytes.  */
+/* Class used to pretty-print an instruction.  */
 
-extern int gdb_pretty_print_insn (struct gdbarch *gdbarch, struct ui_out *uiout,
-				  const struct disasm_insn *insn, int flags);
+class gdb_pretty_print_disassembler
+{
+public:
+  explicit gdb_pretty_print_disassembler (struct gdbarch *gdbarch)
+    : m_di (gdbarch, &m_insn_stb)
+  {}
+
+  /* Prints the instruction INSN into UIOUT and returns the length of
+     the printed instruction in bytes.  */
+  int pretty_print_insn (struct ui_out *uiout, const struct disasm_insn *insn,
+			 int flags);
+
+private:
+  /* Returns the architecture used for disassembling.  */
+  struct gdbarch *arch () { return m_di.arch (); }
+
+  /* The disassembler used for instruction printing.  */
+  gdb_disassembler m_di;
+
+  /* The buffer used to build the instruction string.  The
+     disassembler is initialized with this stream.  */
+  string_file m_insn_stb;
+
+  /* The buffer used to build the raw opcodes string.  */
+  string_file m_opcode_stb;
+};
 
 /* Return the length in bytes of the instruction at address MEMADDR in
    debugged memory.  */