[LLVMbugs] [Bug 8701] New: Completely overlapping memcpys not eliminated

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=8701

           Summary: Completely overlapping memcpys not eliminated
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: benny.kra at gmail.com
                CC: llvmbugs at cs.uiuc.edu


This C code:

===
#include <string.h>

char string1[12];

void foo() {
  memcpy(string1, "Hello World", 12);
  memcpy(string1, "Hello World", 12);
}
===

optimizes to:

===
@string1 = common global [12 x i8] zeroinitializer, align 1
@.str = private constant [12 x i8] c"Hello World\00"

define void @foo() nounwind ssp {
entry:
  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* getelementptr inbounds ([12 x
i8]* @string1, i64 0, i64 0), i8* getelementptr inbounds ([12 x i8]* @.str, i64
0, i64 0), i64 12, i32 1, i1 false)
  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* getelementptr inbounds ([12 x
i8]* @string1, i64 0, i64 0), i8* getelementptr inbounds ([12 x i8]* @.str, i64
0, i64 0), i64 12, i32 1, i1 false)
  ret void
}

declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32,
i1) nounwind
===

the first memcpy is completely superfluous and should be eliminated.

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