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Generalize tail continues (#1298)

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* Generalize tail continues

* Fix DecodeBasicBlock

`Next` and `Branch` would be null, which is not the state expected by
the branch instructions. They end up branching or falling into a block
which is never populated by the `Translator`. This causes an assert to
be fired when building the CFG.

* Clean up Decode overloads

* Do not synchronize when branching into exit block

If we're branching into an exit block, that exit block will tail
continue into another translation which already has a synchronization.

* Remove A32 predicate tail continue

If `block` is not an exit block then the `block.Next` must exist (as
per the last instruction of `block`).

* Throw if decoded 0 blocks

Address gdkchan's feedback

* Rebuild block list instead of setting to null

Address gdkchan's feedback
This commit is contained in:
Ficture Seven 2020-06-18 07:37:21 +04:00 • committed by GitHub
parent 5e724cf24e
commit 2421186d97
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9 changed files with 178 additions and 240 deletions
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97
ARMeilleure/Instructions/InstEmitFlowHelper.cs
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@ -150,17 +150,32 @@ namespace ARMeilleure.Instructions
private static void EmitNativeCall(ArmEmitterContext context, Operand nativeContextPtr, Operand funcAddr, bool isJump = false)
{
context.StoreToContext();
Operand returnAddress;
if (isJump)
{
context.Tailcall(funcAddr, nativeContextPtr);
}
else
{
returnAddress = context.Call(funcAddr, OperandType.I64, nativeContextPtr);
OpCode op = context.CurrOp;
Operand returnAddress = context.Call(funcAddr, OperandType.I64, nativeContextPtr);
context.LoadFromContext();
EmitContinueOrReturnCheck(context, returnAddress);
// Note: The return value of a translated function is always an Int64 with the
// address execution has returned to. We expect this address to be immediately after the
// current instruction, if it isn't we keep returning until we reach the dispatcher.
Operand nextAddr = Const((long)op.Address + op.OpCodeSizeInBytes);
// Try to continue within this block.
// If the return address isn't to our next instruction, we need to return so the JIT can figure out what to do.
Operand lblContinue = context.GetLabel(nextAddr.Value);
// We need to clear out the call flag for the return address before comparing it.
context.BranchIfTrue(lblContinue, context.ICompareEqual(context.BitwiseAnd(returnAddress, Const(~CallFlag)), nextAddr));
context.Return(returnAddress);
}
}
@ -191,46 +206,18 @@ namespace ARMeilleure.Instructions
}
}
private static void EmitContinueOrReturnCheck(ArmEmitterContext context, Operand returnAddress)
{
// Note: The return value of a translated function is always an Int64 with the
// address execution has returned to. We expect this address to be immediately after the
// current instruction, if it isn't we keep returning until we reach the dispatcher.
Operand nextAddr = Const(GetNextOpAddress(context.CurrOp));
// Try to continue within this block.
// If the return address isn't to our next instruction, we need to return so the JIT can figure out what to do.
Operand lblContinue = Label();
// We need to clear out the call flag for the return address before comparing it.
context.BranchIfTrue(lblContinue, context.ICompareEqual(context.BitwiseAnd(returnAddress, Const(~CallFlag)), nextAddr));
context.Return(returnAddress);
context.MarkLabel(lblContinue);
if (context.CurrBlock.Next == null)
{
// No code following this instruction, try and find the next block and jump to it.
EmitTailContinue(context, nextAddr);
}
}
private static ulong GetNextOpAddress(OpCode op)
{
return op.Address + (ulong)op.OpCodeSizeInBytes;
}
public static void EmitTailContinue(ArmEmitterContext context, Operand address, bool allowRejit = false)
{
bool useTailContinue = true; // Left option here as it may be useful if we need to return to managed rather than tail call in future. (eg. for debug)
// Left option here as it may be useful if we need to return to managed rather than tail call in future.
// (eg. for debug)
bool useTailContinue = true;
if (useTailContinue)
{
if (context.HighCq)
{
// If we're doing a tail continue in HighCq, reserve a space in the jump table to avoid calling back to the translator.
// This will always try to get a HighCq version of our continue target as well.
// If we're doing a tail continue in HighCq, reserve a space in the jump table to avoid calling back
// to the translator. This will always try to get a HighCq version of our continue target as well.
EmitJumpTableBranch(context, address, true);
}
else
@ -263,6 +250,7 @@ namespace ARMeilleure.Instructions
{
address = context.BitwiseOr(address, Const(address.Type, (long)CallFlag)); // Set call flag.
Operand fallbackAddr = context.Call(typeof(NativeInterface).GetMethod(nameof(NativeInterface.GetFunctionAddress)), address);
EmitNativeCall(context, fallbackAddr, isJump);
}
@ -273,39 +261,48 @@ namespace ARMeilleure.Instructions
Operand endLabel = Label();
Operand fallbackLabel = Label();
Action<Operand> emitTableEntry = (Operand entrySkipLabel) =>
void EmitTableEntry(Operand entrySkipLabel)
{
// Try to take this entry in the table if its guest address equals 0.
Operand gotResult = context.CompareAndSwap(tableAddress, Const(0L), address);
// Is the address ours? (either taken via CompareAndSwap (0), or what was already here)
context.BranchIfFalse(entrySkipLabel, context.BitwiseOr(context.ICompareEqual(gotResult, address), context.ICompareEqual(gotResult, Const(0L))));
context.BranchIfFalse(entrySkipLabel,
context.BitwiseOr(
context.ICompareEqual(gotResult, address),
context.ICompareEqual(gotResult, Const(0L)))
);
// It's ours, so what function is it pointing to?
Operand targetFunctionPtr = context.Add(tableAddress, Const(8L));
Operand targetFunction = context.Load(OperandType.I64, targetFunctionPtr);
// Call the function.
// We pass in the entry address as the guest address, as the entry may need to be updated by the indirect call stub.
// We pass in the entry address as the guest address, as the entry may need to be updated by the
// indirect call stub.
EmitNativeCallWithGuestAddress(context, targetFunction, tableAddress, isJump);
context.Branch(endLabel);
};
}
// Currently this uses a size of 1, as higher values inflate code size for no real benefit.
for (int i = 0; i < JumpTable.DynamicTableElems; i++)
{
if (i == JumpTable.DynamicTableElems - 1)
{
emitTableEntry(fallbackLabel); // If this is the last entry, avoid emitting the additional label and add.
}
// If this is the last entry, avoid emitting the additional label and add.
EmitTableEntry(fallbackLabel);
}
else
{
Operand nextLabel = Label();
emitTableEntry(nextLabel);
EmitTableEntry(nextLabel);
context.MarkLabel(nextLabel);
tableAddress = context.Add(tableAddress, Const((long)JumpTable.JumpTableStride)); // Move to the next table entry.
// Move to the next table entry.
tableAddress = context.Add(tableAddress, Const((long)JumpTable.JumpTableStride));
}
}
@ -323,16 +320,15 @@ namespace ARMeilleure.Instructions
address = context.ZeroExtend32(OperandType.I64, address);
}
// TODO: Constant folding. Indirect calls are slower in the best case and emit more code so we want to avoid them when possible.
// TODO: Constant folding. Indirect calls are slower in the best case and emit more code so we want to
// avoid them when possible.
bool isConst = address.Kind == OperandKind.Constant;
long constAddr = (long)address.Value;
if (!context.HighCq)
{
// Don't emit indirect calls or jumps if we're compiling in lowCq mode.
// This avoids wasting space on the jump and indirect tables.
// Just ask the translator for the function address.
// Don't emit indirect calls or jumps if we're compiling in lowCq mode. This avoids wasting space on the
// jump and indirect tables. Just ask the translator for the function address.
EmitBranchFallback(context, address, isJump);
}
else if (!isConst)
@ -376,7 +372,8 @@ namespace ARMeilleure.Instructions
Operand funcAddr = context.Load(OperandType.I64, tableEntryPtr);
EmitNativeCallWithGuestAddress(context, funcAddr, address, isJump); // Call the function directly. If it's not present yet, this will call the direct call stub.
// Call the function directly. If it's not present yet, this will call the direct call stub.
EmitNativeCallWithGuestAddress(context, funcAddr, address, isJump);
}
}
}