Jakob Stoklund Olesen 54b6cd6d38 Implement the first half of LiveDebugVariables.
Scan the MachineFunction for DBG_VALUE instructions, and replace them with a
data structure similar to LiveIntervals. The live range of a DBG_VALUE is
determined by propagating it down the dominator tree until a new DBG_VALUE is
found. When a DBG_VALUE lives in a register, its live range is confined to the
live range of the register's value.

LiveDebugVariables runs before coalescing, so DBG_VALUEs are not artificially
extended when registers are joined.

The missing half will recreate DBG_VALUE instructions from the intervals when
register allocation is complete.

The pass is disabled by default. It can be enabled with the temporary command
line option -live-debug-variables.

llvm-svn: 120636
2010-12-02 00:37:37 +00:00
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