Movatterモバイル変換

[0]ホーム
URL:

Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly

 Sign up
Appearance settings

Commit77d643d

Browse files
Dead code elimination forif (typeof(T).IsValueType) (#97080)
@stephentoub found out that for following code:```csharpusing System.Buffers;Foo<Bar>();static T[] Foo<T>(){ if (typeof(T).IsValueType) { return ArrayPool<T>.Shared.Rent(42); } return null!;}class Bar {}```We end up generating `ArrayPool`s of `Bar` even though it's obviously never reachable. The problem is architectural:* We run a whole program analysis phase that tries to figure out things like generic dictionary layouts so that later, in code generation phase, we can inline offsets into generic dictionaries into codegen.* For the above code, whole program analysis decides that the dictionary layout of `Foo<__Canon>` needs a slot for `ArrayPool<!0>`.* Codegen then optimizes out the `IsValueType` branch because `__Canon` is never a valuetype. But we already allocated the dictionary slot and will fill it out, even though it ends up unused due to the optimization.We're going to run into issues like this until#83021 is addressed. Whole program analysis cannot currently assume a certain optimization happens because we don't know whether RyuJIT will do it. The only way we can "optimize" during whole program analysis is if we rewrite IL and give RyuJIT no saying in whether to do an optimization or not. Rewriting the IL is not great because it e.g. causes PGO data to not match. I don't like doing it, but there's nothing else we can do.This change extends dead block elimination to understand `typeof(X).IsValueType`. If we recognize a branch is reachable under this condition, we evaluate whether this is true or false and replace the basic block with nops.
1 parent957ab2f commit77d643d

File tree

2 files changed

+89
-22
lines changed

2 files changed

+89
-22
lines changed

‎src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/FeatureSwitchManager.cs‎

Lines changed: 63 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -591,6 +591,13 @@ private bool TryGetConstantArgument(MethodIL methodIL, byte[] body, OpcodeFlags[
591591
{
592592
returntrue;
593593
}
594+
elseif(method.IsIntrinsic&&method.Nameis"get_IsValueType"
595+
&&method.OwningTypeisMetadataTypemdt
596+
&&mdt.Name=="Type"&&mdt.Namespace=="System"&&mdt.Module==mdt.Context.SystemModule
597+
&&TryExpandTypeIsValueType(methodIL,body,flags,currentOffset,outconstant))
598+
{
599+
returntrue;
600+
}
594601
else
595602
{
596603
constant=0;
@@ -745,6 +752,40 @@ private string GetResourceStringForAccessor(EcmaMethod method)
745752
returnnull;
746753
}
747754

755+
privatestaticboolTryExpandTypeIsValueType(MethodILmethodIL,byte[]body,OpcodeFlags[]flags,intoffset,outintconstant)
756+
{
757+
// We expect to see a sequence:
758+
// ldtoken Foo
759+
// call GetTypeFromHandle
760+
// -> offset points here
761+
constant=0;
762+
constintSequenceLength=10;
763+
if(offset<SequenceLength)
764+
returnfalse;
765+
766+
if((flags[offset-SequenceLength]&OpcodeFlags.InstructionStart)==0)
767+
returnfalse;
768+
769+
ILReaderreader=newILReader(body,offset-SequenceLength);
770+
771+
TypeDesctype=ReadLdToken(refreader,methodIL,flags);
772+
if(type==null)
773+
returnfalse;
774+
775+
if(!ReadGetTypeFromHandle(refreader,methodIL,flags))
776+
returnfalse;
777+
778+
// Dataflow runs on top of uninstantiated IL and we can't answer some questions there.
779+
// Unfortunately this means dataflow will still see code that the rest of the system
780+
// might have optimized away. It should not be a problem in practice.
781+
if(type.IsSignatureVariable)
782+
returnfalse;
783+
784+
constant=type.IsValueType?1:0;
785+
786+
returntrue;
787+
}
788+
748789
privatestaticboolTryExpandTypeEquality(MethodILmethodIL,byte[]body,OpcodeFlags[]flags,intoffset,stringop,outintconstant)
749790
{
750791
// We expect to see a sequence:
@@ -793,37 +834,37 @@ private static bool TryExpandTypeEquality(MethodIL methodIL, byte[] body, Opcode
793834
constant^=1;
794835

795836
returntrue;
837+
}
796838

797-
staticTypeDescReadLdToken(refILReaderreader,MethodILmethodIL,OpcodeFlags[]flags)
798-
{
799-
ILOpcodeopcode=reader.ReadILOpcode();
800-
if(opcode!=ILOpcode.ldtoken)
801-
returnnull;
839+
privatestaticTypeDescReadLdToken(refILReaderreader,MethodILmethodIL,OpcodeFlags[]flags)
840+
{
841+
ILOpcodeopcode=reader.ReadILOpcode();
842+
if(opcode!=ILOpcode.ldtoken)
843+
returnnull;
802844

803-
TypeDesct=(TypeDesc)methodIL.GetObject(reader.ReadILToken());
845+
TypeDesct=(TypeDesc)methodIL.GetObject(reader.ReadILToken());
804846

805-
if((flags[reader.Offset]&OpcodeFlags.BasicBlockStart)!=0)
806-
returnnull;
847+
if((flags[reader.Offset]&OpcodeFlags.BasicBlockStart)!=0)
848+
returnnull;
807849

808-
returnt;
809-
}
850+
returnt;
851+
}
810852

811-
staticboolReadGetTypeFromHandle(refILReaderreader,MethodILmethodIL,OpcodeFlags[]flags)
812-
{
813-
ILOpcodeopcode=reader.ReadILOpcode();
814-
if(opcode!=ILOpcode.call)
815-
returnfalse;
853+
privatestaticboolReadGetTypeFromHandle(refILReaderreader,MethodILmethodIL,OpcodeFlags[]flags)
854+
{
855+
ILOpcodeopcode=reader.ReadILOpcode();
856+
if(opcode!=ILOpcode.call)
857+
returnfalse;
816858

817-
MethodDescmethod=(MethodDesc)methodIL.GetObject(reader.ReadILToken());
859+
MethodDescmethod=(MethodDesc)methodIL.GetObject(reader.ReadILToken());
818860

819-
if(!method.IsIntrinsic||method.Name!="GetTypeFromHandle")
820-
returnfalse;
861+
if(!method.IsIntrinsic||method.Name!="GetTypeFromHandle")
862+
returnfalse;
821863

822-
if((flags[reader.Offset]&OpcodeFlags.BasicBlockStart)!=0)
823-
returnfalse;
864+
if((flags[reader.Offset]&OpcodeFlags.BasicBlockStart)!=0)
865+
returnfalse;
824866

825-
returntrue;
826-
}
867+
returntrue;
827868
}
828869

829870
privatesealedclassSubstitutedMethodIL:MethodIL

‎src/tests/nativeaot/SmokeTests/TrimmingBehaviors/DeadCodeElimination.cs‎

Lines changed: 26 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -21,6 +21,7 @@ public static int Run()
2121
TestArrayElementTypeOperations.Run();
2222
TestStaticVirtualMethodOptimizations.Run();
2323
TestTypeEquals.Run();
24+
TestTypeIsValueType.Run();
2425
TestBranchesInGenericCodeRemoval.Run();
2526
TestUnmodifiableStaticFieldOptimization.Run();
2627
TestUnmodifiableInstanceFieldOptimization.Run();
@@ -355,6 +356,31 @@ public static void Run()
355356
}
356357
}
357358

359+
classTestTypeIsValueType
360+
{
361+
classNever{}
362+
363+
classEver{}
364+
365+
staticvoidGeneric<T>()
366+
{
367+
if(typeof(T).IsValueType)
368+
{
369+
Activator.CreateInstance(typeof(Never));
370+
}
371+
372+
Activator.CreateInstance(typeof(Ever));
373+
}
374+
375+
publicstaticvoidRun()
376+
{
377+
Generic<object>();
378+
379+
ThrowIfPresent(typeof(TestTypeIsValueType),nameof(Never));
380+
ThrowIfNotPresent(typeof(TestTypeIsValueType),nameof(Ever));
381+
}
382+
}
383+
358384
classTestBranchesInGenericCodeRemoval
359385
{
360386
classClassWithUnusedVirtual

0 commit comments

Comments
 (0)
[8]ページ先頭
©2009-2025 Movatter.jp