8367ad18b1
library/modules/std/sched.sx: a generic Fiber + Scheduler over the proven naked swap_context on guarded mmap stacks -- init/spawn/yield_now/suspend_self/wake/run (B1.5a), then Task($R) + go/wait/cancel, a truly-suspending nullary-thunk async layer (B1.4a). go(work) runs a thunk as a real fiber; wait() parks the caller until it completes. Self-contained in sched.sx (io.sx importing it would duplicate the _fib_tramp global asm). Hardened per adversarial review: wake guarded on .suspended (FIFO corruption), suspend_self/yield_now guard a null current, loud mmap/mprotect/OOM/deadlock bails, cancel skips not-yet-run work. Closure-env + heap-Task leaks documented (bounded, default-GPA-invisible). Examples: 1811 (round-robin), 1812 (suspend/wake + spurious-wake guard), 1813 (async interleave + await-suspend + cancel). Also files issue 0155 (scalar-pointer index panics codegen -- non-blocking, found in review).
2.5 KiB
issue 0155 — indexing a scalar pointer (pc[0], pc: *i64) panics at LLVM emission
OPEN. Found incidentally during an adversarial review of the fiber scheduler (a review probe used
pc[0]on a*i64). NOT a fibers-stream blocker — the scheduler uses array-field indexing (ctx.regs[i]) and pointer deref (p.*), never scalar-pointer indexing — so it is filed for its own fix session, not fixed inline.
Symptom
Indexing a pointer-to-scalar value with [i] crashes the compiler:
thread … panic: unresolved type reached LLVM emission — a type resolution
failure was not diagnosed/aborted
src/backend/llvm/types.zig:196:28 toLLVMTypeInfo (.unresolved arm)
src/backend/llvm/types.zig:38 toLLVMType
src/ir/emit_llvm.zig:2564 toLLVMType
Observed: compiler panic (no diagnostic). Expected: either lower pc[i] as
*(pc + i) (C semantics), or emit a clean diagnostic that a bare *T is not
indexable (deref with .*, or use a slice []T). A .unresolved TypeId
reaching LLVM emission is unconditionally a compiler bug (a resolution failure
that was neither diagnosed nor aborted).
Reproduction
#import "modules/std.sx";
main :: () -> i64 {
x : i64 = 5;
pc : *i64 = @x;
return pc[0]; // panics the compiler
}
(repro: issues/0155-scalar-pointer-index-llvm-panic.sx)
Investigation prompt
The sx compiler panics ("unresolved type reached LLVM emission",
src/backend/llvm/types.zig:196) when an index expressionpc[i]is applied to a value of pointer-to-scalar type*T(repro:issues/0155-scalar-pointer-index-llvm-panic.sx). TraceemitIndexGet(src/backend/llvm/ops.zig~1988) and the index-expr lowering insrc/ir/lower/(the.index_exprarm): for a*Tobject, the element type resolves to.unresolvedinstead ofT. Decide the intended semantics first (consultspecs.mdfor whether a bare*Tis indexable): ifpc[i]should mean*(pc + i), fix the index-expr type resolver to yield the pointee typeTfor a*Tobject (mirror the slice/array-pointer arm — seeptrToArrayElem/getElementTypeinsrc/ir/lower/), and verify codegen emits a GEP + load. If a bare*Tis intentionally NOT indexable, emit a diagnostic at the lowering site ("cannot index*T; deref with.*or use a slice") and never let.unresolvedreach emission. Verify:sx runthe repro — expect either5(if indexable) or a clean compile error, never a panic. Then promote the repro to a regression test underexamples/.