[all-commits] [llvm/llvm-project] 4098f5: [mlir][vector] Don't fold in_bounds for negative c...

[Dhairyashil R G via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4098f568c46e06b6df470111868b4c165dd80f4d
      https://github.com/llvm/llvm-project/commit/4098f568c46e06b6df470111868b4c165dd80f4d
  Author: Dhairyashil R G <dhairyashil25 at gmail.com>
  Date:   2026-09-13 (Sun, 13 Sep 2026)

  Changed paths:
    M mlir/lib/Dialect/Vector/IR/VectorOps.cpp
    M mlir/test/Dialect/Vector/canonicalize.mlir

  Log Message:
  -----------
  [mlir][vector] Don't fold in_bounds for negative constant indices (#219681)

`isInBounds` checked only that the transfer *ends* inside the source:

    return cstOp.value() + vectorSize <= sourceSize;

The `in_bounds` attribute promises more than that. Its definition in
VectorOps.td says accesses "(including the starting point)" may run
out-of-bounds when it is "false", so setting it to "true" is a claim
about the start of the transfer as well as its end.

With a negative constant index the two disagree. For

    vector.transfer_read %m[-1] : memref<8xf32>, vector<4xf32>

`-1 + 4 <= 8` holds, so the fold set `in_bounds = [true]`, even though
element -1 is read from outside `%m`.

The same expression also overflows for a large enough index: at `index =
2^63 - 1` the addition wraps and the fold again reports `in_bounds =
[true]`. Computing the bound as `sourceSize - vectorSize` instead avoids
the addition entirely; both operands are static, non-negative dimension
sizes, so the subtraction cannot overflow.

This is a spec-conformance fix, not a live miscompile report. A negative
index into a memref is already undefined behaviour, and the masked
lowering would not have caught it either: the guard
`generateInBoundsCheck` emits in VectorToSCF is `memrefDim > index +
iv`, an upper-bound check only.

Adds three regression tests, each of which fails without the change.

Assisted-by: Claude



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