carbon-lang/toolchain/check/handle_if_expr.cpp

// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#include "toolchain/check/context.h"
#include "toolchain/check/control_flow.h"
#include "toolchain/check/convert.h"
#include "toolchain/check/handle.h"
#include "toolchain/check/literal.h"

namespace Carbon::Check {

auto HandleParseNode(Context& context, Parse::IfExprIfId node_id) -> bool {
  // Alias node_id for if/then/else consistency.
  auto& if_node = node_id;

  auto [cond_node, cond_value_id] = context.node_stack().PopExprWithNodeId();

  // Convert the condition to `bool`, and branch on it.
  cond_value_id = ConvertToBoolValue(context, if_node, cond_value_id);
  context.node_stack().Push(cond_node, cond_value_id);
  auto then_block_id =
      AddDominatedBlockAndBranchIf(context, if_node, cond_value_id);
  auto else_block_id = AddDominatedBlockAndBranch(context, if_node);

  // Start emitting the `then` block.
  context.inst_block_stack().Pop();
  context.inst_block_stack().Push(then_block_id);
  context.region_stack().AddToRegion(then_block_id, node_id);

  context.node_stack().Push(if_node, else_block_id);
  return true;
}

// If the operand is an `IntLiteral`, convert it to a suitably-sized `Int` type.
// TODO: For now we always pick `i32`.
static auto DecayIntLiteralToSizedInt(Context& context, Parse::NodeId node_id,
                                      SemIR::InstId operand_id)
    -> SemIR::InstId {
  if (context.types().GetTypeInstId(
          context.insts().Get(operand_id).type_id()) ==
      SemIR::IntLiteralType::TypeInstId) {
    operand_id = ConvertToValueOfType(
        context, node_id, operand_id,
        MakeIntType(context, node_id, SemIR::IntKind::Signed,
                    context.ints().Add(32)));
  }
  return operand_id;
}

auto HandleParseNode(Context& context, Parse::IfExprThenId node_id) -> bool {
  auto then_value_id = context.node_stack().PopExpr();
  auto else_block_id = context.node_stack().Peek<Parse::NodeKind::IfExprIf>();

  // Convert the first operand to a value.
  then_value_id = ConvertToValueExpr(context, then_value_id);
  then_value_id = DecayIntLiteralToSizedInt(context, node_id, then_value_id);

  // Start emitting the `else` block.
  context.inst_block_stack().Push(else_block_id);
  context.region_stack().AddToRegion(else_block_id, node_id);

  context.node_stack().Push(node_id, then_value_id);
  return true;
}

auto HandleParseNode(Context& context, Parse::IfExprElseId node_id) -> bool {
  if (!context.scope_stack().IsInFunctionScope()) {
    return context.TODO(node_id,
                        "Control flow expressions are currently only supported "
                        "inside functions.");
  }
  // Alias node_id for if/then/else consistency.
  auto& else_node = node_id;

  auto else_value_id = context.node_stack().PopExpr();
  auto then_value_id = context.node_stack().Pop<Parse::NodeKind::IfExprThen>();
  auto [if_node, _] =
      context.node_stack().PopWithNodeId<Parse::NodeKind::IfExprIf>();
  auto cond_value_id = context.node_stack().PopExpr();

  // Convert the `else` value to the `then` value's type, and finish the `else`
  // block.
  // TODO: Find a common type, and convert both operands to it instead.
  auto result_type_id = context.insts().Get(then_value_id).type_id();
  else_value_id =
      ConvertToValueOfType(context, else_node, else_value_id, result_type_id);

  // Create a resumption block and branches to it.
  auto chosen_value_id = AddConvergenceBlockWithArgAndPush(
      context, if_node, {else_value_id, then_value_id});
  SetBlockArgResultBeforeConstantUse(context, chosen_value_id, cond_value_id,
                                     then_value_id, else_value_id);

  // Push the result value.
  context.node_stack().Push(else_node, chosen_value_id);
  return true;
}

}  // namespace Carbon::Check