darling-JavaScriptCore/b3/B3Opcode.h

/*
 * Copyright (C) 2015-2017 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#pragma once

#if ENABLE(B3_JIT)

#include "B3Type.h"
#include "B3Width.h"
#include <wtf/Optional.h>
#include <wtf/StdLibExtras.h>

namespace JSC { namespace B3 {

// Warning: In B3, an Opcode is just one part of a Kind. Kind is used the way that an opcode
// would be used in simple IRs. See B3Kind.h.

enum Opcode : uint8_t {
    // A no-op that returns Void, useful for when you want to remove a value.
    Nop,
    
    // Polymorphic identity, usable with any value type.
    Identity,
        
    // This is an identity, but we prohibit the compiler from realizing this until the bitter end. This can
    // be used to block reassociation and other compiler reasoning, if we find that it's wrong or
    // unprofitable and we need an escape hatch.
    Opaque,

    // Constants. Use the ConstValue* classes. Constants exist in the control flow, so that we can
    // reason about where we would construct them. Large constants are expensive to create.
    Const32,
    Const64,
    ConstDouble,
    ConstFloat,

    // B3 supports non-SSA variables. These are accessed using Get and Set opcodes. Use the
    // VariableValue class. It's a good idea to run fixSSA() to turn these into SSA. The
    // optimizer will do that eventually, but if your input tends to use these opcodes, you
    // should run fixSSA() directly before launching the optimizer.
    Set,
    Get,

    // Gets the base address of a StackSlot.
    SlotBase,

    // The magical argument register. This is viewed as executing at the top of the program
    // regardless of where in control flow you put it, and the compiler takes care to ensure that we
    // don't clobber the value by register allocation or calls (either by saving the argument to the
    // stack or preserving it in a callee-save register). Use the ArgumentRegValue class. The return
    // type is either pointer() (for GPRs) or Double (for FPRs).
    ArgumentReg,

    // The frame pointer. You can put this anywhere in control flow but it will always yield the
    // frame pointer, with a caveat: if our compiler changes the frame pointer temporarily for some
    // silly reason, the FramePointer intrinsic will return where the frame pointer *should* be not
    // where it happens to be right now.
    FramePointer,

    // Polymorphic math, usable with any value type.
    Add,
    Sub,
    Mul,
    Div, // All bets are off as to what will happen when you execute this for -2^31/-1 and x/0.
    UDiv,
    Mod, // All bets are off as to what will happen when you execute this for -2^31%-1 and x%0.
    UMod,

    // Polymorphic negation. Note that we only need this for floating point, since integer negation
    // is exactly like Sub(0, x). But that's not true for floating point. Sub(0, 0) is 0, while
    // Neg(0) is -0. Also, we canonicalize Sub(0, x) into Neg(x) in case of integers.
    Neg,

    // Integer math.
    BitAnd,
    BitOr,
    BitXor,
    Shl,
    SShr, // Arithmetic Shift.
    ZShr, // Logical Shift.
    RotR, // Rotate Right.
    RotL, // Rotate Left.
    Clz, // Count leading zeros.

    // Floating point math.
    Abs,
    Ceil,
    Floor,
    Sqrt,

    // Casts and such.
    // Bitwise Cast of Double->Int64 or Int64->Double
    BitwiseCast,
    // Takes and returns Int32:
    SExt8,
    SExt16,
    // Takes Int32 and returns Int64:
    SExt32,
    ZExt32,
    // Does a bitwise truncation of Int64->Int32 and Double->Float:
    Trunc,
    // Takes ints and returns floating point value. Note that we don't currently provide the opposite operation,
    // because double-to-int conversions have weirdly different semantics on different platforms. Use
    // a patchpoint if you need to do that.
    IToD,
    IToF,
    // Convert between double and float.
    FloatToDouble,
    DoubleToFloat,

    // Polymorphic comparisons, usable with any value type. Returns int32 0 or 1. Note that "Not"
    // is just Equal(x, 0), and "ToBoolean" is just NotEqual(x, 0).
    Equal,
    NotEqual,
    LessThan,
    GreaterThan,
    LessEqual,
    GreaterEqual,

    // Integer comparisons. Returns int32 0 or 1.
    Above,
    Below,
    AboveEqual,
    BelowEqual,

    // Unordered floating point compare: values are equal or either one is NaN.
    EqualOrUnordered,

    // SSA form of conditional move. The first child is evaluated for truthiness. If true, the second child
    // is returned. Otherwise, the third child is returned.
    Select,

    // Memory loads. Opcode indicates how we load and the loaded type. These use MemoryValue.
    // These return Int32:
    Load8Z,
    Load8S,
    Load16Z,
    Load16S,
    // This returns whatever the return type is:
    Load,

    // Memory stores. Opcode indicates how the value is stored. These use MemoryValue.
    // These take an Int32 value:
    Store8,
    Store16,
    // This is a polymorphic store for Int32, Int64, Float, and Double.
    Store,
    
    // Atomic compare and swap that returns a boolean. May choose to do nothing and return false. You can
    // usually assume that this is faster and results in less code than AtomicStrongCAS, though that's
    // not necessarily true on Intel, if instruction selection does its job. Imagine that this opcode is
    // as if you did this atomically:
    //
    // template<typename T>
    // bool AtomicWeakCAS(T expectedValue, T newValue, T* ptr)
    // {
    //     if (!rand())
    //         return false; // Real world example of this: context switch on ARM while doing CAS.
    //     if (*ptr != expectedValue)
    //         return false;
    //     *ptr = newValue;
    //     return true;
    // }
    //
    // Note that all atomics put the pointer last to be consistent with how loads and stores work. This
    // is a goofy tradition, but it's harmless, and better than being inconsistent.
    //
    // Note that weak CAS has no fencing guarantees when it fails. This means that the following
    // transformation is always valid:
    //
    // Before:
    //
    //         Branch(AtomicWeakCAS(expected, new, ptr))
    //       Successors: Then:#success, Else:#fail
    //
    // After:
    //
    //         Branch(Equal(Load(ptr), expected))
    //       Successors: Then:#attempt, Else:#fail
    //     BB#attempt:
    //         Branch(AtomicWeakCAS(expected, new, ptr))
    //       Successors: Then:#success, Else:#fail
    //
    // Both kinds of CAS for non-canonical widths (Width8 and Width16) ignore the irrelevant bits of the
    // input.
    AtomicWeakCAS,
    
    // Atomic compare and swap that returns the old value. Does not have the nondeterminism of WeakCAS.
    // This is a bit more code and a bit slower in some cases, though not by a lot. Imagine that this
    // opcode is as if you did this atomically:
    //
    // template<typename T>
    // T AtomicStrongCAS(T expectedValue, T newValue, T* ptr)
    // {
    //     T oldValue = *ptr;
    //     if (oldValue == expectedValue)
    //         *ptr = newValue;
    //     return oldValue
    // }
    //
    // AtomicStrongCAS sign-extends its result for subwidth operations.
    //
    // Note that AtomicWeakCAS and AtomicStrongCAS sort of have this kind of equivalence:
    //
    // AtomicWeakCAS(@exp, @new, @ptr) == Equal(AtomicStrongCAS(@exp, @new, @ptr), @exp)
    //
    // Assuming that the WeakCAS does not spuriously fail, of course.
    AtomicStrongCAS,
    
    // Atomically ___ a memory location and return the old value. Syntax:
    //
    // @oldValue = AtomicXchg___(@operand, @ptr)
    //
    // For non-canonical widths (Width8 and Width16), these return sign-extended results and ignore the
    // irrelevant bits of their inputs.
    AtomicXchgAdd,
    AtomicXchgAnd,
    AtomicXchgOr,
    AtomicXchgSub,
    AtomicXchgXor,
    
    // FIXME: Maybe we should have AtomicXchgNeg.
    // https://bugs.webkit.org/show_bug.cgi?id=169252
    
    // Atomically exchange a value with a memory location. Syntax:
    //
    // @oldValue = AtomicXchg(@newValue, @ptr)
    AtomicXchg,
    
    // Introduce an invisible dependency for blocking motion of loads with respect to each other. Syntax:
    //
    // @result = Depend(@phantom)
    //
    // This is eventually codegenerated to have local semantics as if we did:
    //
    // @result = $0
    //
    // But it ensures that the users of @result cannot execute until @phantom is computed.
    //
    // The compiler is not allowed to reason about the fact that Depend codegenerates this way. Any kind
    // of transformation or analysis that relies on the insight that Depend is really zero is unsound,
    // because it unlocks reordering of users of @result and @phantom.
    //
    // On X86, this is lowered to a load-load fence and @result folds to zero.
    //
    // On ARM, this is lowered as if like:
    //
    // @result = BitXor(@phantom, @phantom)
    //
    // Except that the compiler never gets an opportunity to simplify out the BitXor.
    Depend,

    // This is used to compute the actual address of a Wasm memory operation. It takes an IntPtr
    // and a pinned register then computes the appropriate IntPtr address. For the use-case of
    // Wasm it is important that the first child initially be a ZExt32 so the top bits are cleared.
    // We do WasmAddress(ZExt32(ptr), ...) so that we can avoid generating extraneous moves in Air.
    WasmAddress,
    
    // This is used to represent standalone fences - i.e. fences that are not part of other
    // instructions. It's expressive enough to expose mfence on x86 and dmb ish/ishst on ARM. On
    // x86, it also acts as a compiler store-store fence in those cases where it would have been a
    // dmb ishst on ARM.
    Fence,

    // This is a regular ordinary C function call, using the system C calling convention. Make sure
    // that the arguments are passed using the right types. The first argument is the callee.
    CCall,

    // This is a patchpoint. Use the PatchpointValue class. This is viewed as behaving like a call,
    // but only emits code via a code generation callback. That callback gets to emit code inline.
    // You can pass a stackmap along with constraints on how each stackmap argument must be passed.
    // It's legal to request that a stackmap argument is in some register and it's legal to request
    // that a stackmap argument is at some offset from the top of the argument passing area on the
    // stack.
    Patchpoint,

    // Checked math. Use the CheckValue class. Like a Patchpoint, this takes a code generation
    // callback. That callback gets to emit some code after the epilogue, and gets to link the jump
    // from the check, and the choice of registers. You also get to supply a stackmap. Note that you
    // are not allowed to jump back into the mainline code from your slow path, since the compiler
    // will assume that the execution of these instructions proves that overflow didn't happen. For
    // example, if you have two CheckAdd's:
    //
    // a = CheckAdd(x, y)
    // b = CheckAdd(x, y)
    //
    // Then it's valid to change this to:
    //
    // a = CheckAdd(x, y)
    // b = Identity(a)
    //
    // This is valid regardless of the callbacks used by the two CheckAdds. They may have different
    // callbacks. Yet, this transformation is valid even if they are different because we know that
    // after the first CheckAdd executes, the second CheckAdd could not have possibly taken slow
    // path. Therefore, the second CheckAdd's callback is irrelevant.
    //
    // Note that the first two children of these operations have ValueRep's as input constraints but do
    // not have output constraints.
    CheckAdd,
    CheckSub,
    CheckMul,

    // Check that side-exits. Use the CheckValue class. Like CheckAdd and friends, this has a
    // stackmap with a generation callback. This takes an int argument that this branches on, with
    // full branch fusion in the instruction selector. A true value jumps to the generator's slow
    // path. Note that the predicate child is has both an input ValueRep. The input constraint must be
    // WarmAny. It will not have an output constraint.
    Check,

    // Special Wasm opcode that takes a Int32, a special pinned gpr and an offset. This node exists
    // to allow us to CSE WasmBoundsChecks if both use the same pointer and one dominates the other.
    // Without some such node B3 would not have enough information about the inner workings of wasm
    // to be able to perform such optimizations.
    WasmBoundsCheck,

    // SSA support, in the style of DFG SSA.
    Upsilon, // This uses the UpsilonValue class.
    Phi,

    // Jump.
    Jump,
    
    // Polymorphic branch, usable with any integer type. Branches if not equal to zero. The 0-index
    // successor is the true successor.
    Branch,

    // Switch. Switches over either Int32 or Int64. Uses the SwitchValue class.
    Switch,
    
    // Multiple entrypoints are supported via the EntrySwitch operation. Place this in the root
    // block and list the entrypoints as the successors. All blocks backwards-reachable from
    // EntrySwitch are duplicated for each entrypoint.
    EntrySwitch,

    // Return. Note that B3 procedures don't know their return type, so this can just return any
    // type.
    Return,

    // This is a terminal that indicates that we will never get here.
    Oops
};

inline bool isCheckMath(Opcode opcode)
{
    switch (opcode) {
    case CheckAdd:
    case CheckSub:
    case CheckMul:
        return true;
    default:
        return false;
    }
}

Optional<Opcode> invertedCompare(Opcode, Type);

inline Opcode constPtrOpcode()
{
    if (is64Bit())
        return Const64;
    return Const32;
}

inline bool isConstant(Opcode opcode)
{
    switch (opcode) {
    case Const32:
    case Const64:
    case ConstDouble:
    case ConstFloat:
        return true;
    default:
        return false;
    }
}

inline Opcode opcodeForConstant(Type type)
{
    switch (type) {
    case Int32: return Const32;
    case Int64: return Const64;
    case Float: return ConstFloat;
    case Double: return ConstDouble;
    default:
        RELEASE_ASSERT_NOT_REACHED();
    }
}

inline bool isDefinitelyTerminal(Opcode opcode)
{
    switch (opcode) {
    case Jump:
    case Branch:
    case Switch:
    case Oops:
    case Return:
        return true;
    default:
        return false;
    }
}

inline bool isLoad(Opcode opcode)
{
    switch (opcode) {
    case Load8Z:
    case Load8S:
    case Load16Z:
    case Load16S:
    case Load:
        return true;
    default:
        return false;
    }
}

inline bool isStore(Opcode opcode)
{
    switch (opcode) {
    case Store8:
    case Store16:
    case Store:
        return true;
    default:
        return false;
    }
}

inline bool isLoadStore(Opcode opcode)
{
    switch (opcode) {
    case Load8Z:
    case Load8S:
    case Load16Z:
    case Load16S:
    case Load:
    case Store8:
    case Store16:
    case Store:
        return true;
    default:
        return false;
    }
}

inline bool isAtom(Opcode opcode)
{
    switch (opcode) {
    case AtomicWeakCAS:
    case AtomicStrongCAS:
    case AtomicXchgAdd:
    case AtomicXchgAnd:
    case AtomicXchgOr:
    case AtomicXchgSub:
    case AtomicXchgXor:
    case AtomicXchg:
        return true;
    default:
        return false;
    }
}

inline bool isAtomicCAS(Opcode opcode)
{
    switch (opcode) {
    case AtomicWeakCAS:
    case AtomicStrongCAS:
        return true;
    default:
        return false;
    }
}

inline bool isAtomicXchg(Opcode opcode)
{
    switch (opcode) {
    case AtomicXchgAdd:
    case AtomicXchgAnd:
    case AtomicXchgOr:
    case AtomicXchgSub:
    case AtomicXchgXor:
    case AtomicXchg:
        return true;
    default:
        return false;
    }
}

inline bool isMemoryAccess(Opcode opcode)
{
    return isAtom(opcode) || isLoadStore(opcode);
}

inline Opcode signExtendOpcode(Width width)
{
    switch (width) {
    case Width8:
        return SExt8;
    case Width16:
        return SExt16;
    default:
        RELEASE_ASSERT_NOT_REACHED();
        return Oops;
    }
}

JS_EXPORT_PRIVATE Opcode storeOpcode(Bank bank, Width width);

} } // namespace JSC::B3

namespace WTF {

class PrintStream;

JS_EXPORT_PRIVATE void printInternal(PrintStream&, JSC::B3::Opcode);

} // namespace WTF

#endif // ENABLE(B3_JIT)