M2compiler-V3/docs/summary_step2.md

V3 step 2 — REAL lowering: the scalar story is complete (done 2026-09-19)

With step 1.9's statements + this section, every scalar kind lowers: INTEGER/CARDINAL-family, BOOLEAN, CHAR, REAL/LONGREAL (widened to d), with conversions, comparisons and full control flow. Suite 30/30 (14 run + 16 reject), LL(1)-clean, zero regressions.

Backend (QbeGen)

• d_ immediates (NormReal); IsImm accepts them; NegFold folds d_ literals (Test2 recipe).
• DeclVar: data $x = { d 0 } for ClReal. DeclConst: zero reals as d 0 (textual IsZeroReal, incl. -0.0); non-zero REALs as d 0 + a recorded runtime =d copy flushed at BeginBody (this qbe rejects d 1.5 in data — same limit Test2 hit, same workaround).
• Threaded isReal through LoadVar (loadd) / StoreVar (stored) / Op3 (=d); Cmp gains ceqd/cned/cltd/cled/cgtd/cged; NegQ via sub d_0.0; new ConvIR (swtof) for INTEGER→REAL assignment widening.

Grammar (isReal threading, Test1 type rules)

• Real literals fold (NormReal, no more 230); / added to MulOp (OpSlash → div, Test2 parity: also defined on integers as truncating division — documented, matches the lenient family).
• VAR x: REAL accepted; loads/stores carry the class flag in Design (var/param/const), SimExpr/Term (arith + unary minus), Expr (comparisons; flag read before the type becomes BOOLEAN).
• Conversions ONLY via assignment (r := 3 → swtof); mixed arithmetic and mixed comparisons stay 211/213; REAL→INTEGER is 210. No implicit anything else.

Tests

t_real → 31 (zero + flushed CONSTs, conversion, all six real comparisons, /, real unary-minus temps, int/real branches) with hand-checked .ssa (flush block, swtof, cgtd all present); t_bad_mixed (i := r) → 210.

Honest leftovers (scalar)

• CHAR arithmetic is 211; enum literals don't lower (use is 230); enum/char subrange bounds are integer-only.
• LONGINT/LONGREAL are aliases (true quads = later step).
• 5 / 2 on integers truncates (Test2 parity, not Wirth /).
• Division by zero traps via QBE/SIGFPE (no language Trap yet — arrives with runtime/syslib/Trap).

Next: step 3 composites (ARRAY/RECORD/SET/POINTER + the locked length-prefixed layout + WITH + IN).