[LLVMbugs] [Bug 8784] New: Optimise mov -1, reg to or

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Dec 13 13:43:12 PST 2010


           Summary: Optimise mov -1, reg to or
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: joerg at NetBSD.org
                CC: llvmbugs at cs.uiuc.edu

[Using AT&T syntax]

The code generator should consider the following transformation:

movl $-1, %eax ==> orl $-1, %eax
movq $-1, %rax ==> orq $-1, %rax

This save 2 (3) Bytes at the cost of a partial dependency on the flags and the
old register state.

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