Integer div and mod by zero previously trapped in hardware (SIGFPE),
uncatchable even inside try/except — a single bad divisor terminated the
process. Both backends now emit a divisor-zero guard before each integer
idiv that raises a catchable EDivByZero exception via the normal exception
machinery, matching standard Pascal/Delphi semantics.
- SysUtils: add EDivByZero = class(Exception) and the _RaiseDivByZero helper
that raises EDivByZero('Division by zero').
- QBE + native x86-64: emit a divisor==0 check before integer div/rem
(32- and 64-bit); on zero, call SysUtils__RaiseDivByZero (which longjmps).
- The guard is emitted only when SysUtils is in scope (EDivByZero resolves
through the symbol table); without SysUtils, division traps as before.
This mirrors Delphi's placement of EDivByZero in System.SysUtils and keeps
the always-linked runtime free of stdlib class machinery.
- Tests: in-process e2e proves the guard does not disturb normal division on
both backends; shell-out cli tests (real compiler + linked stdlib) prove
catchable div/mod-by-zero on both backends.
- Rationale recorded in language-rationale.adoc.
All three fixpoints green (FIXPOINT_OK, NATIVE_FIXPOINT_OK,
NATIVE_INTERNAL_OK); full suite OK (3345 tests).
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