src/tint/lang/msl/writer/raise/binary_polyfill.cc

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#include "src/tint/lang/msl/writer/raise/binary_polyfill.h"

#include <utility>

#include "src/tint/lang/core/ir/builder.h"
#include "src/tint/lang/core/ir/validator.h"
#include "src/tint/lang/msl/ir/builtin_call.h"

namespace tint::msl::writer::raise {
namespace {

/// PIMPL state for the transform.
struct State {
    /// The IR module.
    core::ir::Module& ir;

    /// The IR builder.
    core::ir::Builder b{ir};

    /// The type manager.
    core::type::Manager& ty{ir.Types()};

    /// Process the module.
    void Process() {
        // Find the binary operators that need replacing.
        Vector<core::ir::CoreBinary*, 4> fmod_worklist;
        Vector<core::ir::CoreBinary*, 4> logical_bool_worklist;
        Vector<core::ir::CoreBinary*, 4> signed_integer_arithmetic_worklist;
        Vector<core::ir::CoreBinary*, 4> signed_integer_leftshift_worklist;
        for (auto* inst : ir.Instructions()) {
            if (auto* binary = inst->As<core::ir::CoreBinary>()) {
                auto op = binary->Op();
                auto* lhs_type = binary->LHS()->Type();
                if (op == core::BinaryOp::kModulo && lhs_type->IsFloatScalarOrVector()) {
                    fmod_worklist.Push(binary);
                } else if ((op == core::BinaryOp::kAnd || op == core::BinaryOp::kOr) &&
                           lhs_type->IsBoolScalarOrVector()) {
                    logical_bool_worklist.Push(binary);
                } else if ((op == core::BinaryOp::kAdd || op == core::BinaryOp::kMultiply ||
                            op == core::BinaryOp::kSubtract) &&
                           lhs_type->IsSignedIntegerScalarOrVector()) {
                    signed_integer_arithmetic_worklist.Push(binary);
                } else if (op == core::BinaryOp::kShiftLeft &&
                           lhs_type->IsSignedIntegerScalarOrVector()) {
                    signed_integer_leftshift_worklist.Push(binary);
                }
            }
        }

        // Replace the instructions that we found.
        for (auto* fmod : fmod_worklist) {
            FMod(fmod);
        }
        for (auto* logical_bool : logical_bool_worklist) {
            LogicalBool(logical_bool);
        }
        for (auto* signed_arith : signed_integer_arithmetic_worklist) {
            SignedIntegerArithmetic(signed_arith);
        }
        for (auto* signed_shift_left : signed_integer_leftshift_worklist) {
            SignedIntegerShiftLeft(signed_shift_left);
        }
    }

    /// Replace a floating point modulo binary instruction with the equivalent MSL intrinsic.
    /// @param binary the float point modulo binary instruction
    void FMod(core::ir::CoreBinary* binary) {
        auto* call = b.CallWithResult<msl::ir::BuiltinCall>(
            binary->DetachResult(), msl::BuiltinFn::kFmod, binary->Operands());
        call->InsertBefore(binary);
        binary->Destroy();
    }

    /// Replace a logical boolean binary instruction.
    /// @param binary the logical boolean binary instruction
    void LogicalBool(core::ir::CoreBinary* binary) {
        // MSL does not have boolean overloads for `&` and `|`, so it promotes the operands to
        // integers. Make this explicit in the IR and then convert the result of the binary
        // instruction back to a boolean.
        auto* result_ty = binary->Result(0)->Type();
        auto* int_ty = ty.MatchWidth(ty.u32(), result_ty);
        b.InsertBefore(binary, [&] {
            auto* int_lhs = b.Convert(int_ty, binary->LHS());
            auto* int_rhs = b.Convert(int_ty, binary->RHS());
            auto* int_binary = b.Binary(binary->Op(), int_ty, int_lhs, int_rhs);
            b.ConvertWithResult(binary->DetachResult(), int_binary);
        });
        binary->Destroy();
    }

    /// Replace a signed integer arithmetic instruction.
    /// @param binary the signed integer arithmetic instruction
    void SignedIntegerArithmetic(core::ir::CoreBinary* binary) {
        // MSL does not define the behavior of signed integer overflow, so bitcast the operands to
        // unsigned integers, perform the operation, and then bitcast the result back to a signed
        // integer.
        auto* signed_result_ty = binary->Result(0)->Type();
        auto* unsigned_result_ty = ty.MatchWidth(ty.u32(), signed_result_ty);
        auto* unsigned_lhs_ty = ty.MatchWidth(ty.u32(), binary->LHS()->Type());
        auto* unsigned_rhs_ty = ty.MatchWidth(ty.u32(), binary->RHS()->Type());
        b.InsertBefore(binary, [&] {
            auto* uint_lhs = b.Bitcast(unsigned_lhs_ty, binary->LHS());
            auto* uint_rhs = b.Bitcast(unsigned_rhs_ty, binary->RHS());
            auto* uint_binary = b.Binary(binary->Op(), unsigned_result_ty, uint_lhs, uint_rhs);
            auto* bitcast = b.Bitcast(signed_result_ty, uint_binary);
            binary->Result(0)->ReplaceAllUsesWith(bitcast->Result(0));
        });
        binary->Destroy();
    }

    /// Replace a signed integer shift left instruction.
    /// @param binary the signed integer shift left instruction
    void SignedIntegerShiftLeft(core::ir::CoreBinary* binary) {
        // Left-shifting a negative integer is undefined behavior in C++14 and therefore potentially
        // in MSL too, so we bitcast to an unsigned integer, perform the shift, and bitcast the
        // result back to a signed integer.
        auto* signed_ty = binary->Result(0)->Type();
        auto* unsigned_ty = ty.MatchWidth(ty.u32(), signed_ty);
        b.InsertBefore(binary, [&] {
            auto* unsigned_lhs = b.Bitcast(unsigned_ty, binary->LHS());
            auto* unsigned_binary =
                b.Binary(binary->Op(), unsigned_ty, unsigned_lhs, binary->RHS());
            auto* bitcast = b.Bitcast(signed_ty, unsigned_binary);
            binary->Result(0)->ReplaceAllUsesWith(bitcast->Result(0));
        });
        binary->Destroy();
    }
};

}  // namespace

Result<SuccessType> BinaryPolyfill(core::ir::Module& ir) {
    auto result = ValidateAndDumpIfNeeded(ir, "msl.BinaryPolyfill",
                                          core::ir::Capabilities{
                                              core::ir::Capability::kAllowPointersInStructures,
                                              core::ir::Capability::kAllowPrivateVarsInFunctions,
                                          });
    if (result != Success) {
        return result.Failure();
    }

    State{ir}.Process();

    return Success;
}

}  // namespace tint::msl::writer::raise