From 65902e86b91f984061657bd8cacf239edb53c39d Mon Sep 17 00:00:00 2001 From: David Brazdil Date: Fri, 15 Jan 2016 09:35:13 +0000 Subject: ART: Optimize out redundant NewInstances of String NewInstance of String creates an empty String object before it is replaced by the result of a StringFactory call (String.). If the empty object is never used prior to the call, it can be safely removed (replaced with null in this case). We do not remove the instruction if: - it has a real use (comparison, instanceof, check-cast), or - we are compiling with --debuggable and there is an environment use. If removed and execution deoptimizes before the StringFactory call, the interpreter will see String. being called on a null object. Since the verifier guarantees that the call was made on new-instance in the input bytecode (b/26579108), the interpreter can safely assume that it was optimized out rather than throw NullPointerException. Results (all without --debuggable): - boot.oat: 563/563 removed - Google Maps: 480/480 removed - Google Docs: 819/819 removed Change-Id: I9fdfc50e9dea6299a7327f94327cdfd2b2538079 --- compiler/optimizing/ssa_builder.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'compiler/optimizing/ssa_builder.h') diff --git a/compiler/optimizing/ssa_builder.h b/compiler/optimizing/ssa_builder.h index 28eef6a40c..ccef8ea380 100644 --- a/compiler/optimizing/ssa_builder.h +++ b/compiler/optimizing/ssa_builder.h @@ -57,6 +57,7 @@ class SsaBuilder : public HGraphVisitor { loop_headers_(graph->GetArena()->Adapter(kArenaAllocSsaBuilder)), ambiguous_agets_(graph->GetArena()->Adapter(kArenaAllocSsaBuilder)), ambiguous_asets_(graph->GetArena()->Adapter(kArenaAllocSsaBuilder)), + uninitialized_strings_(graph->GetArena()->Adapter(kArenaAllocSsaBuilder)), locals_for_(graph->GetBlocks().size(), ArenaVector(graph->GetArena()->Adapter(kArenaAllocSsaBuilder)), graph->GetArena()->Adapter(kArenaAllocSsaBuilder)) { @@ -105,6 +106,8 @@ class SsaBuilder : public HGraphVisitor { HPhi* GetFloatDoubleOrReferenceEquivalentOfPhi(HPhi* phi, Primitive::Type type); HArrayGet* GetFloatOrDoubleEquivalentOfArrayGet(HArrayGet* aget); + void RemoveRedundantUninitializedStrings(); + StackHandleScopeCollection* const handles_; // True if types of ambiguous ArrayGets have been resolved. @@ -119,6 +122,7 @@ class SsaBuilder : public HGraphVisitor { ArenaVector ambiguous_agets_; ArenaVector ambiguous_asets_; + ArenaVector uninitialized_strings_; // HEnvironment for each block. ArenaVector> locals_for_; -- cgit v1.2.3-59-g8ed1b