[LLVMbugs] [Bug 4154] New: -fast and -tailcallopt don't combine

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Mon May 4 12:26:03 PDT 2009


           Summary: -fast and -tailcallopt don't combine
           Product: libraries
           Version: 2.5
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Backend: X86
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: arigo at tunes.org
                CC: llvmbugs at cs.uiuc.edu

Created an attachment (id=2951)
 --> (http://llvm.org/bugs/attachment.cgi?id=2951)
wrong result of "llc -fast -tailcallopt"

"llc -fast -tailcallopt" gives wrong results on the small attached file.

The issue is that there is a "addl 4, %esp" after the "call *%eax", which is
(correctly) not there if compiled with "llc -tailcallopt".

This seems to be tailcallopt not generating the correct calls in "fast" mode. 
It was discovered by playing with the JIT compiler.  (Obviously, the call in
question is not meant to be a tail call; this is part of a more complete set of
functions, and some other calls elsewhere are the ones meant to be tail calls.)

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