IfConverter: Split ScanInstructions into 2 functions.

ScanInstructions is now 2 functions:
AnalyzeBranches and ScanInstructions. ScanInstructions also now takes a
pair of arguments delimiting the instructions to be scanned. This will
be used for forked diamond support to re-scan only a portion of the
block.

llvm-svn: 277904
1 file changed