The driver programs for vector tests use a loop to initialize vector-type values one element at a time.  The PNaCl ABI requires the vector element index to be a constant, and the createConstantInsertExtractElementIndexPass() transformation creates an alloca instruction.  When this alloca is inside a loop, it can (and does in the cross tests) cause a stack overflow.

The workaround here is to use a noinline helper function to do the insertelement.

We didn't run into this problem until now because native and sandbox cross tests build the driver in a different way that presumably avoids running the PNaCl ABI simplification passes.

BUG= none
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1560933002 .