[LLVMbugs] [Bug 9215] New: Reassociate zaps nsw/nuw flags even if it doesn't do anything

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9215

           Summary: Reassociate zaps nsw/nuw flags even if it doesn't do
                    anything
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: baldrick at free.fr
                CC: llvmbugs at cs.uiuc.edu


Testcase:
define i32 @add(i32 %x, i32 %y) {
  %s = add nsw i32 %x, %y
  ret i32 %s
}

$ opt -reassociate -S -o - nsw.ll 
; ModuleID = 'nsw.ll'

define i32 @add(i32 %x, i32 %y) {
  %s = add i32 %y, %x
  ret i32 %s
}

What would be great (and should automatically fix this) would be to have
reassociate add a nsw/nuw flag to the results of its reassociations if all
operations that participated were nsw/nuw.

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