[PATCH] Add a shrink-wrapping pass to improve the placement of prologue and epilogue.

[Krzysztof Parzyszek]

I have a patch that does this for Hexagon.  It's implemented as a part of PEI, specifically in HexagonFrameLowering::insertPrologue.

The problem with multiple prologs is that this can increase code size, plus it's a lot harder to identify the set of registers that need to be saved in each prolog.  You don't want to be saving more registers than you need.


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http://reviews.llvm.org/D9210

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