[LLVMbugs] [Bug 14143] New: Call incorrectly marked tail

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=14143

             Bug #: 14143
           Summary: Call incorrectly marked tail
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: rafael.espindola at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Running "opt -S -tailcallelim" in

define void @a(i8* %a, i8* %b) nounwind uwtable {
entry:
  %c = alloca [100 x i8], align 16
  %0 = bitcast [100 x i8]* %c to i8*
  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %b, i8* %0, i64 100, i32 1, i1
false)
  ret void
}

produces

define void @a(i8* %a, i8* %b) nounwind uwtable {
entry:
  %c = alloca [100 x i8], align 16
  %0 = bitcast [100 x i8]* %c to i8*
  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %0, i8* %a, i64 100, i32 1, i1
false)
  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %b, i8* %0, i64 100, i32 1, i1
false)
  ret void
}

which I think is incorrect since "tail call" requires that "callee function
does not access any allocas or varargs in the caller.".

A consequence is that running "opt -S -no-aa -basicaa -dse" on the result
produces:

define void @a(i8* %a, i8* %b) nounwind uwtable {
entry:
  %c = alloca [100 x i8], align 16
  %0 = bitcast [100 x i8]* %c to i8*
  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %b, i8* %0, i64 100, i32 1, i1
false)
  ret void
}

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