release/19.x: [CodeGen] Clear InitUndef pass new register cache between pass runs (#90967) #110603
+85
−85
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PR for backport #110601 which needed an additional test update to cherry-pick.
Original message:
Multiple invocations of the pass could interfere with eachother, preventing some undefs being initialised.
I found it very difficult to create a unit test for this due to it being dependent on particular allocations of a previous function. However, the bug can be observed here: https://godbolt.org/z/7xnMo41Gv with the creation of the illegal instruction
vnsrl.wi v9, v8, 0