A crash/assertion failure in the greedy register allocator was tracked down to a debug instruction being passed to LiveIntervals::getInstructionIndex. Normally this should not occur as debug instructions are collected and removed by LiveDebugVariables before RA, and reinserted afterwards. However, when a function has no debug info, LiveDebugVariables simply strips any debug values that are present as they're not needed (this situation will occur when a function with debug info is inlined into a nodebug function). The problem is, it only removes DBG_VALUE instructions, leaving DBG_LABELs (the cause of the crash).
This patch updates the LiveDebugVariables nodebug path to remove all debug instructions. The test case verifies that DBG_VALUE/DBG_LABEL instructions are present, and that they are stripped.
When -experimental-debug-variable-locations is enabled, certain variable locations are represented by DBG_INSTR_REF instead of DBG_VALUE. The test case verifies that a DBG_INSTR_REF is emitted by the option, and that it is also stripped.