[LLVMbugs] [Bug 23420] New: Exploit LRVH/STRVH/MVCIN for byte swaps

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue May 5 10:52:38 PDT 2015


            Bug ID: 23420
           Summary: Exploit LRVH/STRVH/MVCIN for byte swaps
           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 currently uses the word and doubleword forms of LOAD REVERSED
and STORE REVERSED to optimize byte-swap idioms.

However, the architecture also provides halfword forms of those
instructions which could be exploited likewise.

In addition, the architecture provides a MOVE INVERSE instruction that
can be used to implement a direct memory-to-memory version of byte-swap
(of any length, in particular including halfword, word, and doubleword).

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