From a5c19ce8d200d68a528f2ce0ebff989106c4a933 Mon Sep 17 00:00:00 2001 From: Mark Mendell Date: Wed, 1 Apr 2015 12:51:05 -0400 Subject: [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 --- compiler/optimizing/parallel_move_resolver.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'compiler/optimizing/parallel_move_resolver.h') diff --git a/compiler/optimizing/parallel_move_resolver.h b/compiler/optimizing/parallel_move_resolver.h index 3fa1b37afd..173cffc71e 100644 --- a/compiler/optimizing/parallel_move_resolver.h +++ b/compiler/optimizing/parallel_move_resolver.h @@ -42,10 +42,15 @@ class ParallelMoveResolver : public ValueObject { protected: class ScratchRegisterScope : public ValueObject { public: + // Spill a scratch register if no regs are free. ScratchRegisterScope(ParallelMoveResolver* resolver, int blocked, int if_scratch, int number_of_registers); + // Grab a scratch register only if available. + ScratchRegisterScope(ParallelMoveResolver* resolver, + int blocked, + int number_of_registers); ~ScratchRegisterScope(); int GetRegister() const { return reg_; } @@ -62,6 +67,8 @@ class ParallelMoveResolver : public ValueObject { // Allocate a scratch register for performing a move. The method will try to use // a register that is the destination of a move, but that move has not been emitted yet. int AllocateScratchRegister(int blocked, int if_scratch, int register_count, bool* spilled); + // As above, but return -1 if no free register. + int AllocateScratchRegister(int blocked, int register_count); // Emit a move. virtual void EmitMove(size_t index) = 0; -- cgit v1.2.3-59-g8ed1b