[PATCH] [PowerPC]Adapt fast stack unwinding to work for Power.

[Bill Seurer]

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Comment at: /home/seurer/llvm/llvm-test/projects/compiler-rt/lib/sanitizer_common/sanitizer_stacktrace.h:52
@@ +51,3 @@
+  static const int OFFSET_TO_PC_IN_FRAME = 2;
+  static const bool FAST_UNWIND_MAY_NEED_TO_POP_FRAMES = true;
+#else
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hfinkel wrote:
> What is special about PPC that makes this true?
The offset where the PC is stored is different on ppc than on whatever this was originally written for (from the comments possibly Macintosh).

The stack frame trace for "slow" unwinding does the "pop the frames until we get to pc" behavior so I duplicated that here.  Without popping the extra frames many of the test cases fail.  The checks leave the existing behavior alone for whatever else uses it.

http://reviews.llvm.org/D9259

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