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wasm: lower min/max for floats to compiler_rt

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The min and max builtins in Zig have some intricate behavior
related to floats, that is not replicated with the min and max
wasm instructions or using simple select operations. By lowering
these instructions to compiler_rt, handling around NaNs is done
correctly.

See also https://github.com/WebAssembly/design/issues/214
This commit is contained in:
Robin Voetter 2023-10-14 12:52:31 +02:00
parent 2fe16e072a
commit 9c20449cc5
No known key found for this signature in database
2 changed files with 27 additions and 7 deletions
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28
src/arch/wasm/CodeGen.zig
View File

@ -6253,8 +6253,10 @@ fn airMulWithOverflow(func: *CodeGen, inst: Air.Inst.Index) InnerError!void {
func.finishAir(inst, result_ptr, &.{ extra.lhs, extra.rhs });
}
fn airMaxMin(func: *CodeGen, inst: Air.Inst.Index, op: enum { max, min }) InnerError!void {
fn airMaxMin(func: *CodeGen, inst: Air.Inst.Index, op: Op) InnerError!void {
assert(op == .max or op == .min);
const mod = func.bin_file.base.options.module.?;
const target = mod.getTarget();
const bin_op = func.air.instructions.items(.data)[inst].bin_op;
const ty = func.typeOfIndex(inst);
@ -6269,13 +6271,25 @@ fn airMaxMin(func: *CodeGen, inst: Air.Inst.Index, op: enum { max, min }) InnerE
const lhs = try func.resolveInst(bin_op.lhs);
const rhs = try func.resolveInst(bin_op.rhs);
// operands to select from
try func.lowerToStack(lhs);
try func.lowerToStack(rhs);
_ = try func.cmp(lhs, rhs, ty, if (op == .max) .gt else .lt);
if (ty.zigTypeTag(mod) == .Float) {
var fn_name_buf: [64]u8 = undefined;
const float_bits = ty.floatBits(target);
const fn_name = std.fmt.bufPrint(&fn_name_buf, "{s}f{s}{s}", .{
target_util.libcFloatPrefix(float_bits),
@tagName(op),
target_util.libcFloatSuffix(float_bits),
}) catch unreachable;
const result = try func.callIntrinsic(fn_name, &.{ ty.ip_index, ty.ip_index }, ty, &.{ lhs, rhs });
try func.lowerToStack(result);
} else {
// operands to select from
try func.lowerToStack(lhs);
try func.lowerToStack(rhs);
_ = try func.cmp(lhs, rhs, ty, if (op == .max) .gt else .lt);
// based on the result from comparison, return operand 0 or 1.
try func.addTag(.select);
// based on the result from comparison, return operand 0 or 1.
try func.addTag(.select);
}
// store result in local
const result_ty = if (isByRef(ty, mod)) Type.u32 else ty;

6
test/behavior/maximum_minimum.zig
View File

@ -123,6 +123,12 @@ test "@min/max for floats" {
try expectEqual(x, @min(y, x));
try expectEqual(y, @max(x, y));
try expectEqual(y, @max(y, x));
if (T != comptime_float) {
var nan: T = std.math.nan(T);
try expectEqual(y, @max(nan, y));
try expectEqual(y, @max(y, nan));
}
}
};