[LLVMbugs] [Bug 9246] New: LLVM fails to merge blocks with calls that only differ in attributes.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9246

           Summary: LLVM fails to merge blocks with calls that only differ
                    in attributes.
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: benny.kra at gmail.com
                CC: llvmbugs at cs.uiuc.edu


Created an attachment (id=6177)
 --> (http://llvm.org/bugs/attachment.cgi?id=6177)
preprocessed C testcase

For the attached test case clang -O3 generates

===
define i8* @foo(i8* %x, i8* %y) nounwind ssp {
entry:
  %0 = tail call i64 @llvm.objectsize.i64(i8* %x, i1 false)
  %cmp = icmp eq i64 %0, -1
  br i1 %cmp, label %cond.false, label %cond.true

cond.true:                                        ; preds = %entry
  %call = tail call i8* @__memcpy_chk(i8* %x, i8* %y, i64 42, i64 %0)
  br label %cond.end

cond.false:                                       ; preds = %entry
  %call.i = tail call i8* @__memcpy_chk(i8* %x, i8* %y, i64 42, i64 %0)
nounwind
  br label %cond.end

cond.end:                                         ; preds = %cond.false,
%cond.true
  %cond = phi i8* [ %call, %cond.true ], [ %call.i, %cond.false ]
  ret i8* %cond
}

declare i64 @llvm.objectsize.i64(i8*, i1) nounwind readnone

declare i8* @__memcpy_chk(i8*, i8*, i64, i64) nounwind
===

cond.true and cond.false should be merged, eliminating the icmp+branch.

This happens because darwin10's headers expand memcpy into a normal
__memcpy_chk call and a call to an inlined function. At this point neither
__memcpy_chk have a nounwind attribute. When the inliner inlines the function
it detects that it was "nounwind" and applies the attribute to the inlined
call.

-- 
Configure bugmail: http://llvm.org/bugs/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.