[LLVMbugs] [Bug 23417] New: Support conditional returns and conditional indirect calls

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23417

            Bug ID: 23417
           Summary: Support conditional returns and conditional indirect
                    calls
           Product: libraries
           Version: trunk
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: SystemZ
          Assignee: unassignedbugs at nondot.org
          Reporter: uweigand at de.ibm.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

System z uses an unconditional branch instruction to implement returns
and indirect calls.  However, the BRANCH ON CONDITION instruction could
also be used with a condition field, which would allow implementing
*conditional* returns and *conditional* indirect calls (if circumstances
otherwise allow), e.g. from source code like this:

  if (cond)
    return;

  if (cond)
    func();

This is not yet implemented.

By adding appropriate instructions to PredicateInstruction and related
routines, the IfConversion pass should be able to detect and optimize
those situations.

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