JIT: Make GS cookie phase run on LIR and move it after async phase #122973
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… transformation Functions with GS cookie checks may furthermore shadow parameters to make sure that the GS cookie ends up above all parameters on the stack. This is done by creating a copy of parameters used like a pointer and redirection all uses to act on the shadow. IR is inserted in the beginning of the function to copy the parameters to their shadows. For async this introduces a problem when it comes to implicit byrefs. The shadowing ceremony introduces a pointer to a local (the storage area in the caller) and that pointer remains live across suspension points, resulting in illegal IR. Ideally we would move the shadowing pass to run after the async transformation, but this requires rewriting the analysis from HIR to LIR. This change instead fixes the issue by keeping the analysis where it is, but by delaying the rewrite of the IR until after the async transformation (for async functions only).
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
jakobbotsch
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Jan 7, 2026
jakobbotsch
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Jan 7, 2026
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I think I will spend a bit more time and move the entire phase to unconditionally run on LIR. The current approach means that we are barely testing the LIR version of this. |
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Functions with GS cookie checks may furthermore shadow parameters to make sure that the GS cookie ends up above all parameters on the stack. This is done by creating a copy of parameters used like a pointer and redirecting all uses to act on the shadow. IR is inserted in the beginning of the function to copy the parameters to their shadows.
For async this introduces a problem when it comes to implicit byrefs. The shadowing ceremony introduces a pointer to a local (the storage area in the caller) and that pointer remains live across suspension points, resulting in illegal IR.
This PR moves the GS phase so that it runs after the async transformation. To do so rewrite the analysis to run on LIR and the IR insertion/rewriting to be compatible with LIR.
Fix #122954