At top of generated isel SelectCode() is this:

  if (!N.Val->hasOneUse()) {
    std::map<SDOperand, SDOperand>::iterator CGMI = CodeGenMap.find(N);
    if (CGMI != CodeGenMap.end()) return CGMI->second;
  }

Suppose a DAG like this:

           X
         ^   ^
        /     \
      USE1    USE2

Suppose USE1 is being selected first and during which X is selected and
returned a new node. After this, USE1 is no longer an use of X. During USE2
selection, X will be selected again since it has only one use!

The fix is to always query CodeGenMap.

llvm-svn: 24679