[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/parallel_move_resolver.cc b/compiler/optimizing/parallel_move_resolver.cc
index 9df8f56..4936685 100644
--- a/compiler/optimizing/parallel_move_resolver.cc
+++ b/compiler/optimizing/parallel_move_resolver.cc
@@ -269,6 +269,20 @@
}
+int ParallelMoveResolver::AllocateScratchRegister(int blocked,
+ int register_count) {
+ int scratch = -1;
+ for (int reg = 0; reg < register_count; ++reg) {
+ if ((blocked != reg) && IsScratchLocation(Location::RegisterLocation(reg))) {
+ scratch = reg;
+ break;
+ }
+ }
+
+ return scratch;
+}
+
+
ParallelMoveResolver::ScratchRegisterScope::ScratchRegisterScope(
ParallelMoveResolver* resolver, int blocked, int if_scratch, int number_of_registers)
: resolver_(resolver),
@@ -282,6 +296,16 @@
}
+ParallelMoveResolver::ScratchRegisterScope::ScratchRegisterScope(
+ ParallelMoveResolver* resolver, int blocked, int number_of_registers)
+ : resolver_(resolver),
+ reg_(kNoRegister),
+ spilled_(false) {
+ // We don't want to spill a register if none are free.
+ reg_ = resolver_->AllocateScratchRegister(blocked, number_of_registers);
+}
+
+
ParallelMoveResolver::ScratchRegisterScope::~ScratchRegisterScope() {
if (spilled_) {
resolver_->RestoreScratch(reg_);