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Sema: elide integer comparisons with guaranteed outcomes
This commit is contained in:
Stevie Hryciw
parent
477038abe9
commit
e57e835904
126
src/Sema.zig
126
src/Sema.zig
@ -28460,6 +28460,17 @@ fn cmpNumeric(
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const runtime_src: LazySrcLoc = src: {
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if (try sema.resolveMaybeUndefVal(lhs)) |lhs_val| {
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if (try sema.resolveMaybeUndefVal(rhs)) |rhs_val| {
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// Compare ints: const vs. undefined (or vice versa)
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if (!lhs_val.isUndef() and (lhs_ty.isInt() or lhs_ty_tag == .ComptimeInt) and rhs_ty.isInt() and rhs_val.isUndef()) {
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if (sema.compareIntsOnlyPossibleResult(target, lhs_val, op, rhs_ty)) |res| {
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return if (res) Air.Inst.Ref.bool_true else Air.Inst.Ref.bool_false;
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}
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} else if (!rhs_val.isUndef() and (rhs_ty.isInt() or rhs_ty_tag == .ComptimeInt) and lhs_ty.isInt() and lhs_val.isUndef()) {
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if (sema.compareIntsOnlyPossibleResult(target, rhs_val, op.reverse(), lhs_ty)) |res| {
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return if (res) Air.Inst.Ref.bool_true else Air.Inst.Ref.bool_false;
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}
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}
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if (lhs_val.isUndef() or rhs_val.isUndef()) {
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return sema.addConstUndef(Type.bool);
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}
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@ -28476,9 +28487,23 @@ fn cmpNumeric(
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return Air.Inst.Ref.bool_false;
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}
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} else {
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if (!lhs_val.isUndef() and (lhs_ty.isInt() or lhs_ty_tag == .ComptimeInt) and rhs_ty.isInt()) {
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// Compare ints: const vs. var
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if (sema.compareIntsOnlyPossibleResult(target, lhs_val, op, rhs_ty)) |res| {
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return if (res) Air.Inst.Ref.bool_true else Air.Inst.Ref.bool_false;
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}
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}
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break :src rhs_src;
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}
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} else {
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if (try sema.resolveMaybeUndefVal(rhs)) |rhs_val| {
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if (!rhs_val.isUndef() and (rhs_ty.isInt() or rhs_ty_tag == .ComptimeInt) and lhs_ty.isInt()) {
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// Compare ints: var vs. const
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if (sema.compareIntsOnlyPossibleResult(target, rhs_val, op.reverse(), lhs_ty)) |res| {
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return if (res) Air.Inst.Ref.bool_true else Air.Inst.Ref.bool_false;
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}
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}
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}
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break :src lhs_src;
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}
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};
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@ -28667,6 +28692,107 @@ fn cmpNumeric(
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return block.addBinOp(Air.Inst.Tag.fromCmpOp(op, block.float_mode == .Optimized), casted_lhs, casted_rhs);
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}
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/// Asserts that LHS value is an int or comptime int and not undefined, and that RHS type is an int.
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/// Given a const LHS and an unknown RHS, attempt to determine whether `op` has a guaranteed result.
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/// If it cannot be determined, returns null.
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/// Otherwise returns a bool for the guaranteed comparison operation.
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fn compareIntsOnlyPossibleResult(sema: *Sema, target: std.Target, lhs_val: Value, op: std.math.CompareOperator, rhs_ty: Type) ?bool {
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const rhs_info = rhs_ty.intInfo(target);
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const vs_zero = lhs_val.orderAgainstZeroAdvanced(sema) catch unreachable;
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const is_zero = vs_zero == .eq;
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const is_negative = vs_zero == .lt;
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const is_positive = vs_zero == .gt;
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// Anything vs. zero-sized type has guaranteed outcome.
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if (rhs_info.bits == 0) return switch (op) {
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.eq, .lte, .gte => is_zero,
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.neq, .lt, .gt => !is_zero,
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};
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// Special case for i1, which can only be 0 or -1.
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// Zero and positive ints have guaranteed outcome.
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if (rhs_info.bits == 1 and rhs_info.signedness == .signed) {
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if (is_positive) return switch (op) {
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.gt, .gte, .neq => true,
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.lt, .lte, .eq => false,
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};
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if (is_zero) return switch (op) {
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.gte => true,
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.lt => false,
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.gt, .lte, .eq, .neq => null,
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};
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}
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// Negative vs. unsigned has guaranteed outcome.
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if (rhs_info.signedness == .unsigned and is_negative) return switch (op) {
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.eq, .gt, .gte => false,
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.neq, .lt, .lte => true,
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};
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const sign_adj = @boolToInt(!is_negative and rhs_info.signedness == .signed);
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const req_bits = lhs_val.intBitCountTwosComp(target) + sign_adj;
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// No sized type can have more than 65535 bits.
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// The RHS type operand is either a runtime value or sized (but undefined) constant.
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if (req_bits > 65535) return switch (op) {
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.lt, .lte => is_negative,
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.gt, .gte => is_positive,
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.eq => false,
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.neq => true,
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};
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const fits = req_bits <= rhs_info.bits;
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// Oversized int has guaranteed outcome.
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switch (op) {
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.eq => return if (!fits) false else null,
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.neq => return if (!fits) true else null,
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.lt, .lte => if (!fits) return is_negative,
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.gt, .gte => if (!fits) return !is_negative,
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}
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// For any other comparison, we need to know if the LHS value is
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// equal to the maximum or minimum possible value of the RHS type.
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const edge: struct { min: bool, max: bool } = edge: {
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if (is_zero and rhs_info.signedness == .unsigned) break :edge .{
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.min = true,
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.max = false,
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};
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if (req_bits != rhs_info.bits) break :edge .{
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.min = false,
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.max = false,
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};
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var ty_buffer: Type.Payload.Bits = .{
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.base = .{ .tag = if (is_negative) .int_signed else .int_unsigned },
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.data = @intCast(u16, req_bits),
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};
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const ty = Type.initPayload(&ty_buffer.base);
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const pop_count = lhs_val.popCount(ty, target);
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if (is_negative) {
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break :edge .{
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.min = pop_count == 1,
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.max = false,
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};
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} else {
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break :edge .{
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.min = false,
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.max = pop_count == req_bits - sign_adj,
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};
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}
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};
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assert(fits);
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return switch (op) {
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.lt => if (edge.max) false else null,
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.lte => if (edge.min) true else null,
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.gt => if (edge.min) false else null,
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.gte => if (edge.max) true else null,
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.eq, .neq => unreachable,
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};
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}
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/// Asserts that lhs and rhs types are both vectors.
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fn cmpVector(
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sema: *Sema,
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@ -1756,17 +1756,8 @@ pub const Value = extern union {
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const info = ty.intInfo(target);
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var buffer: Value.BigIntSpace = undefined;
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const operand_bigint = val.toBigInt(&buffer, target);
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var limbs_buffer: [4]std.math.big.Limb = undefined;
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var result_bigint = BigIntMutable{
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.limbs = &limbs_buffer,
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.positive = undefined,
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.len = undefined,
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};
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result_bigint.popCount(operand_bigint, info.bits);
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return result_bigint.toConst().to(u64) catch unreachable;
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const int = val.toBigInt(&buffer, target);
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return @intCast(u64, int.popCount(info.bits));
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},
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}
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}
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@ -158,7 +158,7 @@ test {
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_ = @import("behavior/incomplete_struct_param_tld.zig");
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_ = @import("behavior/inline_switch.zig");
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_ = @import("behavior/int128.zig");
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_ = @import("behavior/int_div.zig");
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_ = @import("behavior/int_comparison_elision.zig");
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_ = @import("behavior/inttoptr.zig");
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_ = @import("behavior/ir_block_deps.zig");
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_ = @import("behavior/math.zig");
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108
test/behavior/int_comparison_elision.zig
Normal file
108
test/behavior/int_comparison_elision.zig
Normal file
@ -0,0 +1,108 @@
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const std = @import("std");
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const minInt = std.math.minInt;
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const maxInt = std.math.maxInt;
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const builtin = @import("builtin");
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test "int comparison elision" {
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testIntEdges(u0);
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testIntEdges(i0);
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testIntEdges(u1);
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testIntEdges(i1);
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testIntEdges(u4);
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testIntEdges(i4);
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// TODO: support int types > 128 bits wide in other backends
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if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
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if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
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if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
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if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
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if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
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// TODO: panic: integer overflow with int types > 65528 bits wide
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// TODO: LLVM generates too many parameters for wasmtime when splitting up int > 64000 bits wide
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testIntEdges(u64000);
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testIntEdges(i64000);
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}
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// All comparisons in this test have a guaranteed result,
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// so one branch of each 'if' should never be analyzed.
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fn testIntEdges(comptime T: type) void {
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const min = minInt(T);
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const max = maxInt(T);
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var runtime_val: T = undefined;
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if (min > runtime_val) @compileError("analyzed impossible branch");
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if (min <= runtime_val) {} else @compileError("analyzed impossible branch");
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if (runtime_val < min) @compileError("analyzed impossible branch");
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if (runtime_val >= min) {} else @compileError("analyzed impossible branch");
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if (min - 1 > runtime_val) @compileError("analyzed impossible branch");
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if (min - 1 >= runtime_val) @compileError("analyzed impossible branch");
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if (min - 1 < runtime_val) {} else @compileError("analyzed impossible branch");
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if (min - 1 <= runtime_val) {} else @compileError("analyzed impossible branch");
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if (min - 1 == runtime_val) @compileError("analyzed impossible branch");
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if (min - 1 != runtime_val) {} else @compileError("analyzed impossible branch");
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if (runtime_val < min - 1) @compileError("analyzed impossible branch");
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if (runtime_val <= min - 1) @compileError("analyzed impossible branch");
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if (runtime_val > min - 1) {} else @compileError("analyzed impossible branch");
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if (runtime_val >= min - 1) {} else @compileError("analyzed impossible branch");
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if (runtime_val == min - 1) @compileError("analyzed impossible branch");
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if (runtime_val != min - 1) {} else @compileError("analyzed impossible branch");
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if (max >= runtime_val) {} else @compileError("analyzed impossible branch");
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if (max < runtime_val) @compileError("analyzed impossible branch");
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if (runtime_val <= max) {} else @compileError("analyzed impossible branch");
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if (runtime_val > max) @compileError("analyzed impossible branch");
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if (max + 1 > runtime_val) {} else @compileError("analyzed impossible branch");
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if (max + 1 >= runtime_val) {} else @compileError("analyzed impossible branch");
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if (max + 1 < runtime_val) @compileError("analyzed impossible branch");
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if (max + 1 <= runtime_val) @compileError("analyzed impossible branch");
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if (max + 1 == runtime_val) @compileError("analyzed impossible branch");
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if (max + 1 != runtime_val) {} else @compileError("analyzed impossible branch");
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if (runtime_val < max + 1) {} else @compileError("analyzed impossible branch");
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if (runtime_val <= max + 1) {} else @compileError("analyzed impossible branch");
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if (runtime_val > max + 1) @compileError("analyzed impossible branch");
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if (runtime_val >= max + 1) @compileError("analyzed impossible branch");
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if (runtime_val == max + 1) @compileError("analyzed impossible branch");
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if (runtime_val != max + 1) {} else @compileError("analyzed impossible branch");
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const undef_const: T = undefined;
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if (min > undef_const) @compileError("analyzed impossible branch");
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if (min <= undef_const) {} else @compileError("analyzed impossible branch");
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if (undef_const < min) @compileError("analyzed impossible branch");
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if (undef_const >= min) {} else @compileError("analyzed impossible branch");
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if (min - 1 > undef_const) @compileError("analyzed impossible branch");
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if (min - 1 >= undef_const) @compileError("analyzed impossible branch");
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if (min - 1 < undef_const) {} else @compileError("analyzed impossible branch");
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if (min - 1 <= undef_const) {} else @compileError("analyzed impossible branch");
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if (min - 1 == undef_const) @compileError("analyzed impossible branch");
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if (min - 1 != undef_const) {} else @compileError("analyzed impossible branch");
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if (undef_const < min - 1) @compileError("analyzed impossible branch");
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if (undef_const <= min - 1) @compileError("analyzed impossible branch");
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if (undef_const > min - 1) {} else @compileError("analyzed impossible branch");
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if (undef_const >= min - 1) {} else @compileError("analyzed impossible branch");
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if (undef_const == min - 1) @compileError("analyzed impossible branch");
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if (undef_const != min - 1) {} else @compileError("analyzed impossible branch");
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if (max >= undef_const) {} else @compileError("analyzed impossible branch");
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if (max < undef_const) @compileError("analyzed impossible branch");
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if (undef_const <= max) {} else @compileError("analyzed impossible branch");
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if (undef_const > max) @compileError("analyzed impossible branch");
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if (max + 1 > undef_const) {} else @compileError("analyzed impossible branch");
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if (max + 1 >= undef_const) {} else @compileError("analyzed impossible branch");
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if (max + 1 < undef_const) @compileError("analyzed impossible branch");
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if (max + 1 <= undef_const) @compileError("analyzed impossible branch");
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if (max + 1 == undef_const) @compileError("analyzed impossible branch");
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if (max + 1 != undef_const) {} else @compileError("analyzed impossible branch");
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if (undef_const < max + 1) {} else @compileError("analyzed impossible branch");
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if (undef_const <= max + 1) {} else @compileError("analyzed impossible branch");
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if (undef_const > max + 1) @compileError("analyzed impossible branch");
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if (undef_const >= max + 1) @compileError("analyzed impossible branch");
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if (undef_const == max + 1) @compileError("analyzed impossible branch");
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if (undef_const != max + 1) {} else @compileError("analyzed impossible branch");
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}
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