[LLVMbugs] [Bug 1628] New: Tail-merging should be more accepting of labels

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Wed Aug 29 09:21:51 PDT 2007


           Summary: Tail-merging should be more accepting of labels
           Product: new-bugs
           Version: unspecified
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: baldrick at free.fr
                CC: llvmbugs at cs.uiuc.edu

I noticed that tail-merging does not merge basic blocks
that are identical except for labels.  It would be possible
to merge such blocks, the new block would simply have to
contain all the labels from the original two blocks.  Why does
this matter?  Because -enable-eh causes *every* call to be
bracketed by labels, not just invokes (the C++ exception
handling personality requires this).  This causes tail-merging
not to happen much.  For example, take any of the tailmerge tests
in CodeGen/ARM and add -enable-eh to the llc parameters.  See
what I mean?  Since -enable-eh is about to be turned on in llvm-gcc,
and may well become the llc default, this seems important.

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