Compressed native PC for stack maps

Compress native PC based on instruction alignment. This reduces the
size of stack maps, boot.oat is 0.4% smaller for arm64.

Test: test-art-host, test-art-target, N6P booting

Change-Id: I2b70eecabda88b06fa80a85688fd992070d54278
diff --git a/compiler/debug/elf_debug_line_writer.h b/compiler/debug/elf_debug_line_writer.h
index 3db7306..18a9165 100644
--- a/compiler/debug/elf_debug_line_writer.h
+++ b/compiler/debug/elf_debug_line_writer.h
@@ -53,7 +53,8 @@
   // Write line table for given set of methods.
   // Returns the number of bytes written.
   size_t WriteCompilationUnit(ElfCompilationUnit& compilation_unit) {
-    const bool is64bit = Is64BitInstructionSet(builder_->GetIsa());
+    const InstructionSet isa = builder_->GetIsa();
+    const bool is64bit = Is64BitInstructionSet(isa);
     const Elf_Addr base_address = compilation_unit.is_code_address_text_relative
         ? builder_->GetText()->GetAddress()
         : 0;
@@ -66,7 +67,7 @@
     std::unordered_map<std::string, size_t> directories_map;
     int code_factor_bits_ = 0;
     int dwarf_isa = -1;
-    switch (builder_->GetIsa()) {
+    switch (isa) {
       case kArm:  // arm actually means thumb2.
       case kThumb2:
         code_factor_bits_ = 1;  // 16-bit instuctions
@@ -103,7 +104,7 @@
         for (uint32_t s = 0; s < code_info.GetNumberOfStackMaps(encoding); s++) {
           StackMap stack_map = code_info.GetStackMapAt(s, encoding);
           DCHECK(stack_map.IsValid());
-          const uint32_t pc = stack_map.GetNativePcOffset(encoding.stack_map_encoding);
+          const uint32_t pc = stack_map.GetNativePcOffset(encoding.stack_map_encoding, isa);
           const int32_t dex = stack_map.GetDexPc(encoding.stack_map_encoding);
           pc2dex_map.push_back({pc, dex});
           if (stack_map.HasDexRegisterMap(encoding.stack_map_encoding)) {