Thumb2 assembler for JNI compiler and optimizing compiler

This provides a programmatic assembler for the thumb2 instruction set for
ARM.  The interface is the same as the ARM assembler and the ARM assembler has
been moved into Arm32Assembler.  The assembler handles most 16 and 32 bit instructions
and also allows relocations due to branch expansion.  It will also rewrite cbz/cbnz
instructions if they go out of range.

It also changes the JNI compiler to use the thumb2 assembler as opposed
to forcing it to use ARM32.  The trampoline compiler still uses ARM due to the
way it returns the address of its generated code.  A trampoline in thumb2 is the
same size as that in ARM anyway (8 bytes).

Provides gtest for testing the thumb2 instruction output.  This gtest only runs
on the host as it uses arm-eabi-objdump to disassemble the generated code.  On the
target the output is not checked but the assembler will still be run to perform
all its checks.

Change-Id: Icd9742b6f13541bec5b23097896727392e3a6fb6

1 files changed, 4 insertions, 0 deletions

diff --git a/compiler/trampolines/trampoline_compiler.cc b/compiler/trampolines/trampoline_compiler.cc
index 24378b41aa..ac84d6ae40 100644
--- a/compiler/trampolines/trampoline_compiler.cc
+++ b/compiler/trampolines/trampoline_compiler.cc
@@ -30,6 +30,10 @@ namespace art {
 namespace arm {
 static const std::vector<uint8_t>* CreateTrampoline(EntryPointCallingConvention abi,
                                                     ThreadOffset<4> offset) {
+  // NOTE: the assembler used here is ARM, not Thumb.  This is because the address
+  // returned by this function is a pointer and for thumb we would have to set the
+  // bottom bit.  It doesn't matter since the instructions generated are the same
+  // size anyway.
   std::unique_ptr<ArmAssembler> assembler(static_cast<ArmAssembler*>(Assembler::Create(kArm)));
 
   switch (abi) {