empty MBB results in incorrect MBB2IdxMap and Idx2MBBMap

[llvmbot]

Bugzilla Link	2232
Resolution	FIXED
Resolved on	Aug 21, 2008 19:03
Version	unspecified
OS	Windows NT
Reporter	LLVM Bugzilla Contributor

Extended Description

In the LiveIntervalAnalysis::runOnMachineFunction, there is a code to
compute the MBB2IdxMap and Idx2MBBMap, by remembering for each MBB its start and end instruction numbers.

If an MBB is empty, the end index will be larger than the start in MBB2IdxMap, and multiple entries of .first Idx2MBBMap will identical. On some platforms this causes an assert later (in e.g. LiveIntervals::findLiveinMBBs std::lower_bound), and possibly incorrect search behaviour.

[llvmbot]

The only way to fix this, as far as I can tell, is to treat an empty MBB as if it has a single instruction.

[llvmbot]

Owen is doing some work on LIA. :-)

[llvmbot]

This was fixed a month or so ago.