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RegAlloc: do not consider liveins to EH-pad successors as liveout.

Authored by t.p.northover on Apr 29 2021, 4:31 AM.

Description

RegAlloc: do not consider liveins to EH-pad successors as liveout.

These registers get defined by the runtime, not the block being allocated, and
treating them as preassigned in RegAllocFast adds extra pressure, sometimes
enough to make the function unallocatable.

Details