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    <head>
      <base href="http://llvm.org/bugs/" />
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - Prefetch not supported"
   href="http://llvm.org/bugs/show_bug.cgi?id=20692">20692</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Prefetch not supported
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libraries
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Backend: PowerPC
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>nlewycky@google.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Testcase:
; ModuleID = 'p.c' (aka. "void test(char *x) { __builtin_prefetch(x, 1); }")
target datalayout = "E-m:e-i64:64-n32:64"
target triple = "powerpc64--linux-gnu"

; Function Attrs: nounwind
define void @test(i8* nocapture %x) {
entry:
  tail call void @llvm.prefetch(i8* %x, i32 1, i32 3, i32 1)
  ret void
}

; Function Attrs: nounwind
declare void @llvm.prefetch(i8* nocapture, i32, i32, i32) nounwind


If you run that, you get:
nlewycky@ducttape:~$ llc p.ll
LLVM ERROR: Cannot select: 0x320f110: ch = Prefetch 0x31dd410, 0x320edf8,
0x320ef00, 0x320f008, 0x320ef00<ST1[%x]> [ORD=2] [ID=5]
  0x320edf8: i64,ch = CopyFromReg 0x31dd410, 0x320ecf0 [ORD=1] [ID=4]
    0x320ecf0: i64 = Register %vreg0 [ID=1]
  0x320ef00: i32 = Constant<1> [ID=2]
  0x320f008: i32 = Constant<3> [ID=3]
  0x320ef00: i32 = Constant<1> [ID=2]
In function: test</pre>
        </div>
      </p>
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