[optimizing] Improve x86 parallel moves/swaps
Add a new constructor to ScratchRegisterScope that will supply a
register if there is a free one, but not spill to force one. Use this
to generated alternate code that doesn't use a temporary, as the
spill/restore of a register generates extra instructions that aren't
necessary on x86.
Here is the benefit for a 32 bit memory-to-memory exchange with no
free registers:
< 50 push eax
< 53 push ebx
< 8B44244C mov eax, [esp + 76]
< 8B5C246C mov ebx, [esp + 108]
< 8944246C mov [esp + 108], eax
< 895C244C mov [esp + 76], ebx
< 5B pop ebx
< 58 pop eax
---
> FF742444 push [esp + 68]
> FF742468 push [esp + 104]
> 8F44244C pop [esp + 72]
> 8F442468 pop [esp + 100]
Avoid using xchg instruction, as it is slow on smaller processors.
Change-Id: Id29ee3abd998577baaee552d55d23e60ae0c7871
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>
diff --git a/compiler/optimizing/code_generator_x86.h b/compiler/optimizing/code_generator_x86.h
index e6e7fb7..b2420e4 100644
--- a/compiler/optimizing/code_generator_x86.h
+++ b/compiler/optimizing/code_generator_x86.h
@@ -106,6 +106,7 @@
X86Assembler* GetAssembler() const;
private:
+ void Exchange(Register reg1, Register Reg2);
void Exchange(Register reg, int mem);
void Exchange(int mem1, int mem2);
void Exchange32(XmmRegister reg, int mem);