[llvm] Turn off reverse iteration of SmallPtrSet by default

[mgrang]

Summary

Turn off reverse iteration of SmallPtrSet by default since it causes
builtbots to crash. Will re-enable it once I have a fix.

[mgrang]

Internally, we only build llvm for ARM targets. The buildbot crashes are only on some of the non-ARM tests:
http://lab.llvm.org:8080/green/job/clang-stage1-cmake-RA-incremental_check/31314/testReport/junit/LLVM

I will build other targets and try to figure out a fix and then re-enable the default behavior.

[probinson]

The ones that first pinged me were the self-host bots. Build clang, then use that clang to build clang again. Mostly clang itself was crashing.

[mehdi_amini]

I fixed it as of r289626 (hopefully).

Please, if the build is broken, either

• submit the fix *without* pre-commits review.
• or revert the patch immediately and submit a new review that includes the fix.

[mehdi_amini]

(And it was showing up on a stage-1, no need to bootstrap)

[qcolombet]

Hi,

I would rather just revert the patch for now instead of disabling the feature.
Also, when bots are broken, like Mehdi said, skip pre-commit review and reverts are cheap :).

Cheers,
-Quentin

[mgrang]

Patch no longer valid.

include/llvm/ADT/SmallPtrSet.h

 #include <cstdlib>
 #include <initializer_list>
 #include <iterator>
 #include <utility>
 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
 namespace llvm {
 template <class T = void> struct ReverseIterate { static bool value; };
-template <class T> bool ReverseIterate<T>::value = true;
+template <class T> bool ReverseIterate<T>::value = false;
 }
 #endif
 
 namespace llvm {
 
 /// SmallPtrSetImplBase - This is the common code shared among all the
 /// SmallPtrSet<>'s, which is almost everything.  SmallPtrSet has two modes, one
 /// for small and one for large sets.

lib/Support/CommandLine.cpp

 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
 namespace llvm {
 // If LLVM_ENABLE_ABI_BREAKING_CHECKS is set the flag -mllvm -reverse-iterate
 // can be used to toggle forward/reverse iteration of unordered containers.
 // This will help uncover differences in codegen caused due to undefined
 // iteration order.
 static cl::opt<bool, true> ReverseIteration("reverse-iterate",
-  cl::location(ReverseIterate<bool>::value), cl::init(true));
+  cl::location(ReverseIterate<bool>::value), cl::init(false));
 }
 #endif
 
 //===----------------------------------------------------------------------===//
 // Template instantiations and anchors.
 //
 namespace llvm {
 namespace cl {