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stage2: implementation of @setEvalBranchQuota:
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`@setEvalBranchQuota` can be called before the comptime/inline call
stack is created.

For example:

```zig
@setEvalBranchQuota(100);
comptime {
    while (true) {}
}
```

Here we need to set the branch_quota before the comptime block creates a
scope for the branch_count.
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@g-w1 @andrewrk
g-w1 authored and andrewrk committed Jan 4, 2021
1 parent aa0906e commit 638f93e
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Showing 5 changed files with 76 additions and 5 deletions.
25 changes: 21 additions & 4 deletions src/Module.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -765,6 +765,8 @@ pub const Scope = struct {
label: ?Label = null,
inlining: ?*Inlining,
is_comptime: bool,
/// Shared to sub-blocks.
branch_quota: *u32,

pub const InstTable = std.AutoHashMap(*zir.Inst, *Inst);

Expand Down Expand Up @@ -792,8 +794,7 @@ pub const Scope = struct {

pub const Shared = struct {
caller: ?*Fn,
branch_count: u64,
branch_quota: u64,
branch_count: u32,
};
};

Expand Down Expand Up @@ -1104,6 +1105,8 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
var inst_table = Scope.Block.InstTable.init(self.gpa);
defer inst_table.deinit();

var branch_quota: u32 = 1000;

var block_scope: Scope.Block = .{
.parent = null,
.inst_table = &inst_table,
Expand All @@ -1113,6 +1116,7 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
.arena = &decl_arena.allocator,
.inlining = null,
.is_comptime = false,
.branch_quota = &branch_quota,
};
defer block_scope.instructions.deinit(self.gpa);

Expand Down Expand Up @@ -1297,6 +1301,8 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
var decl_inst_table = Scope.Block.InstTable.init(self.gpa);
defer decl_inst_table.deinit();

var branch_quota: u32 = 1000;

var block_scope: Scope.Block = .{
.parent = null,
.inst_table = &decl_inst_table,
Expand All @@ -1306,6 +1312,7 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
.arena = &decl_arena.allocator,
.inlining = null,
.is_comptime = true,
.branch_quota = &branch_quota,
};
defer block_scope.instructions.deinit(self.gpa);

Expand Down Expand Up @@ -1367,6 +1374,7 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
var var_inst_table = Scope.Block.InstTable.init(self.gpa);
defer var_inst_table.deinit();

var branch_quota_vi: u32 = 1000;
var inner_block: Scope.Block = .{
.parent = null,
.inst_table = &var_inst_table,
Expand All @@ -1376,6 +1384,7 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
.arena = &gen_scope_arena.allocator,
.inlining = null,
.is_comptime = true,
.branch_quota = &branch_quota_vi,
};
defer inner_block.instructions.deinit(self.gpa);
try zir_sema.analyzeBody(self, &inner_block, .{
Expand Down Expand Up @@ -1494,6 +1503,8 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
var inst_table = Scope.Block.InstTable.init(self.gpa);
defer inst_table.deinit();

var branch_quota: u32 = 1000;

var block_scope: Scope.Block = .{
.parent = null,
.inst_table = &inst_table,
Expand All @@ -1503,6 +1514,7 @@ fn astGenAndAnalyzeDecl(self: *Module, decl: *Decl) !bool {
.arena = &analysis_arena.allocator,
.inlining = null,
.is_comptime = true,
.branch_quota = &branch_quota,
};
defer block_scope.instructions.deinit(self.gpa);

Expand Down Expand Up @@ -1875,6 +1887,8 @@ pub fn analyzeFnBody(self: *Module, decl: *Decl, func: *Fn) !void {
defer decl.typed_value.most_recent.arena.?.* = arena.state;
var inst_table = Scope.Block.InstTable.init(self.gpa);
defer inst_table.deinit();
var branch_quota: u32 = 1000;

var inner_block: Scope.Block = .{
.parent = null,
.inst_table = &inst_table,
Expand All @@ -1884,6 +1898,7 @@ pub fn analyzeFnBody(self: *Module, decl: *Decl, func: *Fn) !void {
.arena = &arena.allocator,
.inlining = null,
.is_comptime = false,
.branch_quota = &branch_quota,
};
defer inner_block.instructions.deinit(self.gpa);

Expand Down Expand Up @@ -3466,7 +3481,9 @@ pub fn addSafetyCheck(mod: *Module, parent_block: *Scope.Block, ok: *Inst, panic
.arena = parent_block.arena,
.inlining = parent_block.inlining,
.is_comptime = parent_block.is_comptime,
.branch_quota = parent_block.branch_quota,
};

defer fail_block.instructions.deinit(mod.gpa);

_ = try mod.safetyPanic(&fail_block, ok.src, panic_id);
Expand Down Expand Up @@ -3532,10 +3549,10 @@ pub fn identifierTokenString(mod: *Module, scope: *Scope, token: ast.TokenIndex)
pub fn emitBackwardBranch(mod: *Module, block: *Scope.Block, src: usize) !void {
const shared = block.inlining.?.shared;
shared.branch_count += 1;
if (shared.branch_count > shared.branch_quota) {
if (shared.branch_count > block.branch_quota.*) {
// TODO show the "called from here" stack
return mod.fail(&block.base, src, "evaluation exceeded {d} backwards branches", .{
shared.branch_quota,
block.branch_quota.*,
});
}
}
15 changes: 15 additions & 0 deletions src/astgen.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2317,6 +2317,19 @@ fn compileError(mod: *Module, scope: *Scope, call: *ast.Node.BuiltinCall) InnerE
return addZIRUnOp(mod, scope, src, .compileerror, target);
}

fn setEvalBranchQuota(mod: *Module, scope: *Scope, call: *ast.Node.BuiltinCall) InnerError!*zir.Inst {
try ensureBuiltinParamCount(mod, scope, call, 1);
const tree = scope.tree();
const src = tree.token_locs[call.builtin_token].start;
const params = call.params();
const target = try expr(mod, scope, .none, params[0]);
const u32_type = try addZIRInstConst(mod, scope, src, .{
.ty = Type.initTag(.type),
.val = Value.initTag(.u32_type),
});
return addZIRUnOp(mod, scope, src, .setevalbranchquota, try rlWrap(mod, scope, .{ .ty = u32_type }, target));
}

fn typeOf(mod: *Module, scope: *Scope, rl: ResultLoc, call: *ast.Node.BuiltinCall) InnerError!*zir.Inst {
const tree = scope.tree();
const arena = scope.arena();
Expand Down Expand Up @@ -2362,6 +2375,8 @@ fn builtinCall(mod: *Module, scope: *Scope, rl: ResultLoc, call: *ast.Node.Built
return rlWrap(mod, scope, rl, try import(mod, scope, call));
} else if (mem.eql(u8, builtin_name, "@compileError")) {
return compileError(mod, scope, call);
} else if (mem.eql(u8, builtin_name, "@setEvalBranchQuota")) {
return setEvalBranchQuota(mod, scope, call);
} else {
return mod.failTok(scope, call.builtin_token, "invalid builtin function: '{s}'", .{builtin_name});
}
Expand Down
4 changes: 4 additions & 0 deletions src/zir.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,8 @@ pub const Inst = struct {
coerce_to_ptr_elem,
/// Emit an error message and fail compilation.
compileerror,
/// Changes the maximum number of backwards branches that compile-time code execution can use before giving up and making a compile error.
setevalbranchquota,
/// Conditional branch. Splits control flow based on a boolean condition value.
condbr,
/// Special case, has no textual representation.
Expand Down Expand Up @@ -347,6 +349,7 @@ pub const Inst = struct {
.anyframe_type,
.bitnot,
.import,
.setevalbranchquota,
=> UnOp,

.add,
Expand Down Expand Up @@ -535,6 +538,7 @@ pub const Inst = struct {
.switch_range,
.typeof_peer,
.resolve_inferred_alloc,
.setevalbranchquota,
=> false,

.@"break",
Expand Down
22 changes: 21 additions & 1 deletion src/zir_sema.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ pub fn analyzeInst(mod: *Module, scope: *Scope, old_inst: *zir.Inst) InnerError!
.mut_slice_type => return analyzeInstSimplePtrType(mod, scope, old_inst.castTag(.mut_slice_type).?, true, .Slice),
.ptr_type => return analyzeInstPtrType(mod, scope, old_inst.castTag(.ptr_type).?),
.store => return analyzeInstStore(mod, scope, old_inst.castTag(.store).?),
.setevalbranchquota => return analyzeInstSetEvalBranchQuota(mod, scope, old_inst.castTag(.setevalbranchquota).?),
.str => return analyzeInstStr(mod, scope, old_inst.castTag(.str).?),
.int => {
const big_int = old_inst.castTag(.int).?.positionals.int;
Expand Down Expand Up @@ -486,6 +487,18 @@ fn analyzeInstStoreToInferredPtr(
return mod.storePtr(scope, inst.base.src, bitcasted_ptr, value);
}

fn analyzeInstSetEvalBranchQuota(
mod: *Module,
scope: *Scope,
inst: *zir.Inst.UnOp,
) InnerError!*Inst {
const b = try mod.requireFunctionBlock(scope, inst.base.src);
const quota = @truncate(u32, try resolveInt(mod, scope, inst.positionals.operand, Type.initTag(.u32)));
if (b.branch_quota.* < quota)
b.branch_quota.* = quota;
return mod.constVoid(scope, inst.base.src);
}

fn analyzeInstStore(mod: *Module, scope: *Scope, inst: *zir.Inst.BinOp) InnerError!*Inst {
const ptr = try resolveInst(mod, scope, inst.positionals.lhs);
const value = try resolveInst(mod, scope, inst.positionals.rhs);
Expand Down Expand Up @@ -594,6 +607,7 @@ fn analyzeInstLoop(mod: *Module, scope: *Scope, inst: *zir.Inst.Loop) InnerError
.arena = parent_block.arena,
.inlining = parent_block.inlining,
.is_comptime = parent_block.is_comptime,
.branch_quota = parent_block.branch_quota,
};
defer child_block.instructions.deinit(mod.gpa);

Expand All @@ -619,6 +633,7 @@ fn analyzeInstBlockFlat(mod: *Module, scope: *Scope, inst: *zir.Inst.Block, is_c
.label = null,
.inlining = parent_block.inlining,
.is_comptime = parent_block.is_comptime or is_comptime,
.branch_quota = parent_block.branch_quota,
};
defer child_block.instructions.deinit(mod.gpa);

Expand Down Expand Up @@ -666,6 +681,7 @@ fn analyzeInstBlock(mod: *Module, scope: *Scope, inst: *zir.Inst.Block, is_compt
}),
.inlining = parent_block.inlining,
.is_comptime = is_comptime or parent_block.is_comptime,
.branch_quota = parent_block.branch_quota,
};
const merges = &child_block.label.?.merges;

Expand Down Expand Up @@ -867,7 +883,6 @@ fn analyzeInstCall(mod: *Module, scope: *Scope, inst: *zir.Inst.Call) InnerError
// Otherwise we pass on the shared data from the parent scope.
var shared_inlining = Scope.Block.Inlining.Shared{
.branch_count = 0,
.branch_quota = 1000,
.caller = b.func,
};
// This one is shared among sub-blocks within the same callee, but not
Expand Down Expand Up @@ -896,7 +911,9 @@ fn analyzeInstCall(mod: *Module, scope: *Scope, inst: *zir.Inst.Call) InnerError
.label = null,
.inlining = &inlining,
.is_comptime = is_comptime_call,
.branch_quota = b.branch_quota,
};

const merges = &child_block.inlining.?.merges;

defer child_block.instructions.deinit(mod.gpa);
Expand Down Expand Up @@ -1417,6 +1434,7 @@ fn analyzeInstSwitchBr(mod: *Module, scope: *Scope, inst: *zir.Inst.SwitchBr) In
.arena = parent_block.arena,
.inlining = parent_block.inlining,
.is_comptime = parent_block.is_comptime,
.branch_quota = parent_block.branch_quota,
};
defer case_block.instructions.deinit(mod.gpa);

Expand Down Expand Up @@ -1960,6 +1978,7 @@ fn analyzeInstCondBr(mod: *Module, scope: *Scope, inst: *zir.Inst.CondBr) InnerE
.arena = parent_block.arena,
.inlining = parent_block.inlining,
.is_comptime = parent_block.is_comptime,
.branch_quota = parent_block.branch_quota,
};
defer true_block.instructions.deinit(mod.gpa);
try analyzeBody(mod, &true_block, inst.positionals.then_body);
Expand All @@ -1973,6 +1992,7 @@ fn analyzeInstCondBr(mod: *Module, scope: *Scope, inst: *zir.Inst.CondBr) InnerE
.arena = parent_block.arena,
.inlining = parent_block.inlining,
.is_comptime = parent_block.is_comptime,
.branch_quota = parent_block.branch_quota,
};
defer false_block.instructions.deinit(mod.gpa);
try analyzeBody(mod, &false_block, inst.positionals.else_body);
Expand Down
15 changes: 15 additions & 0 deletions test/stage2/cbe.zig
View file
Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,22 @@ pub fn addCases(ctx: *TestContext) !void {
\\}
, "");
}
{
var case = ctx.exeFromCompiledC("@setEvalBranchQuota", .{});

case.addCompareOutput(
\\export fn main() i32 {
\\ @setEvalBranchQuota(1001);
\\ const y = rec(1001);
\\ return y - 1;
\\}
\\
\\inline fn rec(n: usize) usize {
\\ if (n <= 1) return n;
\\ return rec(n - 1);
\\}
, "");
}
ctx.c("empty start function", linux_x64,
\\export fn _start() noreturn {
\\ unreachable;
Expand Down

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