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Optimize type casts #14420

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Oct 13, 2017
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Optimize type casts #14420

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7532f08
JIT: optimize type casts
AndyAyersMS Oct 10, 2017
1e1f4c9
address PR feedback
AndyAyersMS Oct 13, 2017
2a8c566
add some test cases
AndyAyersMS Oct 13, 2017
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2 changes: 2 additions & 0 deletions src/jit/compiler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3156,6 +3156,8 @@ class Compiler
CORINFO_RESOLVED_TOKEN* pResolvedToken,
bool isCastClass);

GenTree* impOptimizeCastClassOrIsInst(GenTree* op1, CORINFO_RESOLVED_TOKEN* pResolvedToken, bool isCastClass);

bool VarTypeIsMultiByteAndCanEnreg(var_types type,
CORINFO_CLASS_HANDLE typeClass,
unsigned* typeSize,
Expand Down
229 changes: 173 additions & 56 deletions src/jit/importer.cpp
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Expand Up @@ -9762,6 +9762,99 @@ var_types Compiler::impGetByRefResultType(genTreeOps oper, bool fUnsigned, GenTr
return type;
}

//------------------------------------------------------------------------
// impOptimizeCastClassOrIsInst: attempt to resolve a cast when jitting
//
// Arguments:
// op1 -- value to cast
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// Arguments:
//    <argument1-name> - Description of argument 1
//    <argument2-name> - Description of argument 2

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Fixed (though I happen to like -- better).

// pResolvedToken -- resolved token for type to cast to
// isCastClass -- true if this is a castclass, false if isinst
//
// Return Value:
// tree representing optimized cast, or null if no optimization possible

GenTree* Compiler::impOptimizeCastClassOrIsInst(GenTree* op1, CORINFO_RESOLVED_TOKEN* pResolvedToken, bool isCastClass)
{
assert(op1->TypeGet() == TYP_REF);

// Don't optimize for minopts or debug codegen.
if (opts.compDbgCode || opts.MinOpts())
{
return nullptr;
}

// See what we know about the type of the object being cast.
bool isExact = false;
bool isNonNull = false;
CORINFO_CLASS_HANDLE fromClass = gtGetClassHandle(op1, &isExact, &isNonNull);
GenTree* optResult = nullptr;

if (fromClass != nullptr)
{
CORINFO_CLASS_HANDLE toClass = pResolvedToken->hClass;
JITDUMP("\nConsidering optimization of %s from %s%p (%s) to %p (%s)\n", isCastClass ? "castclass" : "isinst",
isExact ? "exact " : "", fromClass, info.compCompHnd->getClassName(fromClass), toClass,
info.compCompHnd->getClassName(toClass));

// Perhaps we know if the cast will succeed or fail.
TypeCompareState castResult = info.compCompHnd->compareTypesForCast(fromClass, toClass);

if (castResult == TypeCompareState::Must)
{
// Cast will succeed, result is simply op1.
JITDUMP("Cast will succeed, optimizing to simply return input\n");
return op1;
}
else if (castResult == TypeCompareState::MustNot)
{
// See if we can sharpen exactness by looking for final classes
if (!isExact)
{
DWORD flags = info.compCompHnd->getClassAttribs(fromClass);
DWORD flagsMask = CORINFO_FLG_FINAL | CORINFO_FLG_MARSHAL_BYREF | CORINFO_FLG_CONTEXTFUL |
CORINFO_FLG_VARIANCE | CORINFO_FLG_ARRAY;
isExact = ((flags & flagsMask) == CORINFO_FLG_FINAL);
}

// Cast to exact type will fail. Handle case where we have
// an exact type (that is, fromClass is not a subtype)
// and we're not going to throw on failure.
if (isExact && !isCastClass)
{
JITDUMP("Cast will fail, optimizing to return null\n");
GenTree* result = gtNewIconNode(0, TYP_REF);

// If the cast was fed by a box, we can remove that too.
if (op1->IsBoxedValue())
{
JITDUMP("Also removing upstream box\n");
gtTryRemoveBoxUpstreamEffects(op1);
}

return result;
}
else if (isExact)
{
JITDUMP("Not optimizing failing castclass (yet)\n");
}
else
{
JITDUMP("Can't optimize since fromClass is inexact\n");
}
}
else
{
JITDUMP("Result of cast unknown, must generate runtime test\n");
}
}
else
{
JITDUMP("\nCan't optimize since fromClass is unknown\n");
}

return nullptr;
}

//------------------------------------------------------------------------
// impCastClassOrIsInstToTree: build and import castclass/isinst
//
Expand Down Expand Up @@ -10203,6 +10296,7 @@ void Compiler::impImportBlockCode(BasicBlock* block)
var_types lclTyp, ovflType = TYP_UNKNOWN;
GenTreePtr op1 = DUMMY_INIT(NULL);
GenTreePtr op2 = DUMMY_INIT(NULL);
GenTree* optTree = nullptr;
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I would prefer to create new scopes under CEE_ISINST and CASTCLASS: and declare optTree there.

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Sure, will do.

GenTreeArgList* args = nullptr; // What good do these "DUMMY_INIT"s do?
GenTreePtr newObjThisPtr = DUMMY_INIT(NULL);
bool uns = DUMMY_INIT(false);
Expand Down Expand Up @@ -14262,43 +14356,54 @@ void Compiler::impImportBlockCode(BasicBlock* block)

op1 = impPopStack().val;

#ifdef FEATURE_READYTORUN_COMPILER
if (opts.IsReadyToRun())
optTree = impOptimizeCastClassOrIsInst(op1, &resolvedToken, false);

if (optTree != nullptr)
{
impPushOnStack(optTree, tiRetVal);
}
else
{
GenTreeCall* opLookup =
impReadyToRunHelperToTree(&resolvedToken, CORINFO_HELP_READYTORUN_ISINSTANCEOF, TYP_REF,
gtNewArgList(op1));
usingReadyToRunHelper = (opLookup != nullptr);
op1 = (usingReadyToRunHelper ? opLookup : op1);

if (!usingReadyToRunHelper)
#ifdef FEATURE_READYTORUN_COMPILER
if (opts.IsReadyToRun())
{
// TODO: ReadyToRun: When generic dictionary lookups are necessary, replace the lookup call
// and the isinstanceof_any call with a single call to a dynamic R2R cell that will:
// 1) Load the context
// 2) Perform the generic dictionary lookup and caching, and generate the appropriate stub
// 3) Perform the 'is instance' check on the input object
// Reason: performance (today, we'll always use the slow helper for the R2R generics case)
GenTreeCall* opLookup =
impReadyToRunHelperToTree(&resolvedToken, CORINFO_HELP_READYTORUN_ISINSTANCEOF, TYP_REF,
gtNewArgList(op1));
usingReadyToRunHelper = (opLookup != nullptr);
op1 = (usingReadyToRunHelper ? opLookup : op1);

op2 = impTokenToHandle(&resolvedToken, nullptr, FALSE);
if (op2 == nullptr)
{ // compDonotInline()
return;
if (!usingReadyToRunHelper)
{
// TODO: ReadyToRun: When generic dictionary lookups are necessary, replace the lookup call
// and the isinstanceof_any call with a single call to a dynamic R2R cell that will:
// 1) Load the context
// 2) Perform the generic dictionary lookup and caching, and generate the appropriate
// stub
// 3) Perform the 'is instance' check on the input object
// Reason: performance (today, we'll always use the slow helper for the R2R generics case)

op2 = impTokenToHandle(&resolvedToken, nullptr, FALSE);
if (op2 == nullptr)
{ // compDonotInline()
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What does the comment compDonotInline() mean here?
Should it be deleted or tested?
It is tested later on on line 14400

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We can change it to an assert that compilation failed. assert(compDonotInline());

return;
}
}
}
}

if (!usingReadyToRunHelper)
if (!usingReadyToRunHelper)
#endif
{
op1 = impCastClassOrIsInstToTree(op1, op2, &resolvedToken, false);
}
if (compDonotInline())
{
return;
}
{
op1 = impCastClassOrIsInstToTree(op1, op2, &resolvedToken, false);
}
if (compDonotInline())
{
return;
}

impPushOnStack(op1, tiRetVal);
impPushOnStack(op1, tiRetVal);
}

break;

Expand Down Expand Up @@ -14796,43 +14901,55 @@ void Compiler::impImportBlockCode(BasicBlock* block)
// and op2 to contain code that creates the type handle corresponding to typeRef
CASTCLASS:

#ifdef FEATURE_READYTORUN_COMPILER
if (opts.IsReadyToRun())
optTree = impOptimizeCastClassOrIsInst(op1, &resolvedToken, true);

if (optTree != nullptr)
{
impPushOnStack(optTree, tiRetVal);
}
else
{
GenTreeCall* opLookup = impReadyToRunHelperToTree(&resolvedToken, CORINFO_HELP_READYTORUN_CHKCAST,
TYP_REF, gtNewArgList(op1));
usingReadyToRunHelper = (opLookup != nullptr);
op1 = (usingReadyToRunHelper ? opLookup : op1);

if (!usingReadyToRunHelper)
#ifdef FEATURE_READYTORUN_COMPILER
if (opts.IsReadyToRun())
{
// TODO: ReadyToRun: When generic dictionary lookups are necessary, replace the lookup call
// and the chkcastany call with a single call to a dynamic R2R cell that will:
// 1) Load the context
// 2) Perform the generic dictionary lookup and caching, and generate the appropriate stub
// 3) Check the object on the stack for the type-cast
// Reason: performance (today, we'll always use the slow helper for the R2R generics case)
GenTreeCall* opLookup =
impReadyToRunHelperToTree(&resolvedToken, CORINFO_HELP_READYTORUN_CHKCAST, TYP_REF,
gtNewArgList(op1));
usingReadyToRunHelper = (opLookup != nullptr);
op1 = (usingReadyToRunHelper ? opLookup : op1);

op2 = impTokenToHandle(&resolvedToken, nullptr, FALSE);
if (op2 == nullptr)
{ // compDonotInline()
return;
if (!usingReadyToRunHelper)
{
// TODO: ReadyToRun: When generic dictionary lookups are necessary, replace the lookup call
// and the chkcastany call with a single call to a dynamic R2R cell that will:
// 1) Load the context
// 2) Perform the generic dictionary lookup and caching, and generate the appropriate
// stub
// 3) Check the object on the stack for the type-cast
// Reason: performance (today, we'll always use the slow helper for the R2R generics case)

op2 = impTokenToHandle(&resolvedToken, nullptr, FALSE);
if (op2 == nullptr)
{ // compDonotInline()
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Again we have a comment compDonotInline()

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Let's address those in a subsequent PR, as there are a bunch more of them scattered about.

return;
}
}
}
}

if (!usingReadyToRunHelper)
if (!usingReadyToRunHelper)
#endif
{
op1 = impCastClassOrIsInstToTree(op1, op2, &resolvedToken, true);
}
if (compDonotInline())
{
return;
}
{
op1 = impCastClassOrIsInstToTree(op1, op2, &resolvedToken, true);
}
if (compDonotInline())
{
return;
}

/* Push the result back on the stack */
impPushOnStack(op1, tiRetVal);
/* Push the result back on the stack */
impPushOnStack(op1, tiRetVal);
}
break;

case CEE_THROW:
Expand Down
49 changes: 4 additions & 45 deletions src/mscorlib/src/System/Runtime/CompilerServices/AsyncMethodBuilder.cs
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Expand Up @@ -387,33 +387,14 @@ public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(
{
IAsyncStateMachineBox box = GetStateMachineBox(ref stateMachine);

// TODO https://github.com/dotnet/coreclr/issues/12877:
// Once the JIT is able to recognize "awaiter is ITaskAwaiter" and "awaiter is IConfiguredTaskAwaiter",
// use those in order to a) consolidate a lot of this code, and b) handle all Task/Task<T> and not just
// the few types special-cased here. For now, handle common {Configured}TaskAwaiter. Having the types
// explicitly listed here allows the JIT to generate the best code for them; otherwise we'll fall through
// to the later workaround.
if (typeof(TAwaiter) == typeof(TaskAwaiter) ||
typeof(TAwaiter) == typeof(TaskAwaiter<object>) ||
typeof(TAwaiter) == typeof(TaskAwaiter<string>) ||
typeof(TAwaiter) == typeof(TaskAwaiter<byte[]>) ||
typeof(TAwaiter) == typeof(TaskAwaiter<bool>) ||
typeof(TAwaiter) == typeof(TaskAwaiter<byte>) ||
typeof(TAwaiter) == typeof(TaskAwaiter<int>) ||
typeof(TAwaiter) == typeof(TaskAwaiter<long>))
// TThe null tests here ensure that the jit can optimize away the interface
// tests when TAwaiter is is a ref type.
if ((null != (object)default(TAwaiter)) && (awaiter is ITaskAwaiter))
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Is it worth a comment indicating why the null check is necessary? Or you'll be following up with subsequent changes to remove that, too?

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@AndyAyersMS AndyAyersMS Oct 13, 2017 •
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The jit needs this check or it will leave casts around in some instantations. I will add a comment.

{
ref TaskAwaiter ta = ref Unsafe.As<TAwaiter, TaskAwaiter>(ref awaiter); // relies on TaskAwaiter/TaskAwaiter<T> having the same layout
TaskAwaiter.UnsafeOnCompletedInternal(ta.m_task, box, continueOnCapturedContext: true);
}
else if (
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable.ConfiguredTaskAwaiter) ||
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable<object>.ConfiguredTaskAwaiter) ||
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable<string>.ConfiguredTaskAwaiter) ||
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable<byte[]>.ConfiguredTaskAwaiter) ||
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable<bool>.ConfiguredTaskAwaiter) ||
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable<byte>.ConfiguredTaskAwaiter) ||
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable<int>.ConfiguredTaskAwaiter) ||
typeof(TAwaiter) == typeof(ConfiguredTaskAwaitable<long>.ConfiguredTaskAwaiter))
else if ((null != (object)default(TAwaiter)) && (awaiter is IConfiguredTaskAwaiter))
{
ref ConfiguredTaskAwaitable.ConfiguredTaskAwaiter ta = ref Unsafe.As<TAwaiter, ConfiguredTaskAwaitable.ConfiguredTaskAwaiter>(ref awaiter);
TaskAwaiter.UnsafeOnCompletedInternal(ta.m_task, box, ta.m_continueOnCapturedContext);
Expand Down Expand Up @@ -450,21 +431,6 @@ public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(
TaskAwaiter.UnsafeOnCompletedInternal(vta.AsTask(), box, vta._continueOnCapturedContext);
}

// To catch all Task/Task<T> awaits, do the currently more expensive interface checks.
// Eventually these and the above Task/Task<T> checks should be replaced by "is" checks,
// once that's recognized and optimized by the JIT. We do these after all of the hardcoded
// checks above so that they don't incur the costs of these checks.
else if (InterfaceIsCheckWorkaround<TAwaiter>.IsITaskAwaiter)
{
ref TaskAwaiter ta = ref Unsafe.As<TAwaiter, TaskAwaiter>(ref awaiter);
TaskAwaiter.UnsafeOnCompletedInternal(ta.m_task, box, continueOnCapturedContext: true);
}
else if (InterfaceIsCheckWorkaround<TAwaiter>.IsIConfiguredTaskAwaiter)
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The InterfaceIsCheckWorkaround class could then also be deleted.

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It's gone now.

{
ref ConfiguredTaskAwaitable.ConfiguredTaskAwaiter ta = ref Unsafe.As<TAwaiter, ConfiguredTaskAwaitable.ConfiguredTaskAwaiter>(ref awaiter);
TaskAwaiter.UnsafeOnCompletedInternal(ta.m_task, box, ta.m_continueOnCapturedContext);
}

// The awaiter isn't specially known. Fall back to doing a normal await.
else
{
Expand Down Expand Up @@ -922,13 +888,6 @@ internal static Task<TResult> CreateCacheableTask<TResult>(TResult result) =>
new Task<TResult>(false, result, (TaskCreationOptions)InternalTaskOptions.DoNotDispose, default(CancellationToken));
}

/// <summary>Temporary workaround for https://github.com/dotnet/coreclr/issues/12877.</summary>
internal static class InterfaceIsCheckWorkaround<TAwaiter>
{
internal static readonly bool IsITaskAwaiter = typeof(TAwaiter).GetInterface("ITaskAwaiter") != null;
internal static readonly bool IsIConfiguredTaskAwaiter = typeof(TAwaiter).GetInterface("IConfiguredTaskAwaiter") != null;
}

/// <summary>
/// An interface implemented by all <see cref="AsyncStateMachineBox{TStateMachine, TResult}"/> instances, regardless of generics.
/// </summary>
Expand Down
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