7238eea084
While fixing 0083 (attempt 5) noticed a distinct, pre-existing bug: writing to a Vector component (`v.x = 1.0`) aborts with "unresolved type reached LLVM emission" in emitStore. Reading a lane works; a literal lane count triggers it, so it is NOT the lane-count class. Confirmed reproducible on the pristine pre-attempt-5 compiler (not introduced by the lane-count fix). The standard vector idiom (`.[…]` construction + component reads / arithmetic, examples/1500) is unaffected. Filed for a separate session; not worked around here.
57 lines
2.8 KiB
Markdown
57 lines
2.8 KiB
Markdown
# 0086 — writing to a Vector lane (`v.x = …`) panics with "unresolved type reached LLVM emission"
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## Symptom
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Assigning to a component of a `Vector` local — `v.x = 1.0` (also `.y` / `.z` /
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`.w`) — aborts the compiler with the internal panic:
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```
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thread … panic: unresolved type reached LLVM emission — a type resolution
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failure was not diagnosed/aborted
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src/backend/llvm/types.zig:175 toLLVMTypeInfo (.unresolved arm @panic)
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src/backend/llvm/ops.zig:358 emitStore (.pointer => toLLVMType(p.pointee))
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```
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READING a lane (`x := v.x`) is fine; only the STORE side hits it. The init form
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(`= ---` undefined vs `= .[…]` literal) does not matter — both panic once a lane
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is written. A literal lane count (`Vector(3, f32)`) triggers it, so this is NOT
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the lane-count resolution class (issue 0083); it is a distinct bug in the
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vector-lane **store** path, where the store's pointee type resolves to the
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`.unresolved` sentinel instead of the lane element type.
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Discovered while fixing issue 0083 (attempt 5). It is pre-existing and orthogonal
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— confirmed by reproducing on the pristine pre-0083-attempt-5 compiler — so it was
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NOT introduced by the lane-count fix. The standard vector idiom (construct via a
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`.[…]` literal / a constructor function returning `.[…]`, then read components or
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use vector arithmetic, as in `examples/1500-vectors-vector-math.sx`) is
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unaffected; only component ASSIGNMENT is broken.
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## Reproduction
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```sx
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#import "modules/std.sx";
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main :: () {
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v : Vector(3, f32) = .[0.0, 0.0, 0.0];
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v.x = 1.0; // panic here
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print("x={}\n", v.x);
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}
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```
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`./zig-out/bin/sx run` panics. Removing the `v.x = 1.0` line (read-only) prints
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`x=0.000000` and exits 0.
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## Investigation prompt
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A store to a `Vector` lane (`v.x = …`) lowers a pointer-to-lane whose pointee
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type reaches LLVM as `.unresolved`, so `emitStore`
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(`src/backend/llvm/ops.zig:358`, the `.pointer => toLLVMType(p.pointee)` arm)
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hits the `.unresolved` tripwire panic in
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`src/backend/llvm/types.zig:175`. The lane READ path computes the lane element
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type correctly, so compare the lvalue/store lowering for a vector-component
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assignment against the rvalue/load path — the component-write path is likely
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building the lane pointer's pointee from a vector `.x`/`.y`/`.z`/`.w` field
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resolution that returns `.unresolved` (or a vector field-access that resolves the
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element type on load but not on store). Find where a `Vector` swizzle/component
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assignment lowers its destination pointer (grep for vector component handling in
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`lower.zig` assignment lowering and in the LLVM `emitStore` GEP path) and resolve
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the lane element type there the same way the load path does. Verify with the
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repro (expect `x=1.000000`) plus a `.[…]`-init write and a write to each of
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`.x/.y/.z/.w` on a 4-lane vector, then `zig build && zig build test && bash
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tests/run_examples.sh` green.
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