An untyped float literal defaults to f64, so in an f32 context it was
materialized as f64 then bit-truncated by a raw MOVSS (low-32 reinterpret)
rather than narrowed -- e.g. `let x: f32 = 2.0f32; x * 3.0` multiplied by
0.0f. Twelve byte-id-gate-blind both-wrong miscompiles, all this one cause
(compare, binop, call-arg, struct-field, array-elem against an untyped
literal).
Broaden coerce_floatlit to stamp the untyped fconst type_=f32 across the
f32-context sites (assign rhs, call-arg, struct-field, array-elem) and to
descend the implicit-cast shapes (peel unary +/-/cast, recurse binop
operands AND the binop node, recurse arrlit elems), mirroring harec's
lower_implicit_cast. The existing CVTSD2SS gate then fires; cgen is
unchanged. f64 contexts are untouched -- the stamp is gated on TY_F32.
Surfaced by the float codegen sub-hunt (= the deferred #120). Pinned by
test/lang/f32_untyped_narrow_test.ww (22 value-asserting rows incl. f64
controls; reddens on revert).
Hojun-Cho
e7effe5f57