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AstGen: emit as instructions for branching expressions

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There is a mechanism to avoid redundant `as` ZIR instructions which is
to pass `ResultLoc.coerced_ty` instead of `ResultLoc.ty` when it is
known by AstGen that Sema will do the coercion.

This commit downgrades `coerced_ty` to `ty` when a result location
passes through an expression that branches, such as `if`, `switch`,
`while`, and `for`, causing the `as` ZIR instruction to be emitted.

This ensures that the type of a result location will be applied to, e.g.
a `comptime_int` on either side of a branch on a runtime condition.
This commit is contained in:
Andrew Kelley 2022-01-15 23:13:44 -07:00
parent 7c6f5d26ea
commit 7f41e20802
3 changed files with 31 additions and 22 deletions
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25
src/AstGen.zig
View File

@ -281,6 +281,15 @@ pub const ResultLoc = union(enum) {
},
}
}
/// Turns a `coerced_ty` back into a `ty`. Should be called at branch points
/// such as if and switch expressions.
fn br(rl: ResultLoc) ResultLoc {
return switch (rl) {
.coerced_ty => |ty| .{ .ty = ty },
else => rl,
};
}
};
pub const align_rl: ResultLoc = .{ .ty = .u16_type };
@ -748,15 +757,15 @@ fn expr(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) InnerEr
.field_access => return fieldAccess(gz, scope, rl, node),
.float_literal => return floatLiteral(gz, rl, node),
.if_simple => return ifExpr(gz, scope, rl, node, tree.ifSimple(node)),
.@"if" => return ifExpr(gz, scope, rl, node, tree.ifFull(node)),
.if_simple => return ifExpr(gz, scope, rl.br(), node, tree.ifSimple(node)),
.@"if" => return ifExpr(gz, scope, rl.br(), node, tree.ifFull(node)),
.while_simple => return whileExpr(gz, scope, rl, node, tree.whileSimple(node)),
.while_cont => return whileExpr(gz, scope, rl, node, tree.whileCont(node)),
.@"while" => return whileExpr(gz, scope, rl, node, tree.whileFull(node)),
.while_simple => return whileExpr(gz, scope, rl.br(), node, tree.whileSimple(node)),
.while_cont => return whileExpr(gz, scope, rl.br(), node, tree.whileCont(node)),
.@"while" => return whileExpr(gz, scope, rl.br(), node, tree.whileFull(node)),
.for_simple => return forExpr(gz, scope, rl, node, tree.forSimple(node)),
.@"for" => return forExpr(gz, scope, rl, node, tree.forFull(node)),
.for_simple => return forExpr(gz, scope, rl.br(), node, tree.forSimple(node)),
.@"for" => return forExpr(gz, scope, rl.br(), node, tree.forFull(node)),
.slice_open => {
const lhs = try expr(gz, scope, .ref, node_datas[node].lhs);
@ -943,7 +952,7 @@ fn expr(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) InnerEr
.error_set_decl => return errorSetDecl(gz, rl, node),
.array_access => return arrayAccess(gz, scope, rl, node),
.@"comptime" => return comptimeExprAst(gz, scope, rl, node),
.@"switch", .switch_comma => return switchExpr(gz, scope, rl, node),
.@"switch", .switch_comma => return switchExpr(gz, scope, rl.br(), node),
.@"nosuspend" => return nosuspendExpr(gz, scope, rl, node),
.@"suspend" => return suspendExpr(gz, scope, node),

14
test/behavior/array_llvm.zig
View File

@ -179,3 +179,17 @@ test "access the null element of a null terminated array" {
try S.doTheTest();
comptime try S.doTheTest();
}
test "type deduction for array subscript expression" {
const S = struct {
fn doTheTest() !void {
var array = [_]u8{ 0x55, 0xAA };
var v0 = true;
try expect(@as(u8, 0xAA) == array[if (v0) 1 else 0]);
var v1 = false;
try expect(@as(u8, 0x55) == array[if (v1) 1 else 0]);
}
};
try S.doTheTest();
comptime try S.doTheTest();
}

14
test/behavior/array_stage1.zig
View File

@ -4,20 +4,6 @@ const mem = std.mem;
const expect = testing.expect;
const expectEqual = testing.expectEqual;
test "type deduction for array subscript expression" {
const S = struct {
fn doTheTest() !void {
var array = [_]u8{ 0x55, 0xAA };
var v0 = true;
try expect(@as(u8, 0xAA) == array[if (v0) 1 else 0]);
var v1 = false;
try expect(@as(u8, 0x55) == array[if (v1) 1 else 0]);
}
};
try S.doTheTest();
comptime try S.doTheTest();
}
test "sentinel element count towards the ABI size calculation" {
const S = struct {
fn doTheTest() !void {