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[SROA] Add a debugging tool which shuffles the slices sequence prior to

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sorting it. This helps uncover latent reliance on the original ordering
which aren't guaranteed to be preserved by std::sort (but often are),
and which are based on the use-def chain orderings which also aren't
(technically) guaranteed.

Only available in C++11 debug builds, and behind a flag to prevent noise
at the moment, but this is generally useful so figured I'd put it in the
tree rather than keeping it out-of-tree.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202106 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2014-02-25 03:59:29 +00:00
parent 2516e7fb22
commit eb1b5ba880
1 changed files with 19 additions and 0 deletions
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19
lib/Transforms/Scalar/SROA.cpp
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@ -51,10 +51,17 @@
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/TimeValue.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#if __cplusplus >= 201103L && !defined(NDEBUG)
// We only use this for a debug check in C++11
#include <random>
#endif
using namespace llvm;
STATISTIC(NumAllocasAnalyzed, "Number of allocas analyzed for replacement");
@ -73,6 +80,11 @@ STATISTIC(NumVectorized, "Number of vectorized aggregates");
static cl::opt<bool>
ForceSSAUpdater("force-ssa-updater", cl::init(false), cl::Hidden);
/// Hidden option to enable randomly shuffling the slices to help uncover
/// instability in their order.
static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices",
cl::init(false), cl::Hidden);
namespace {
/// \brief A custom IRBuilder inserter which prefixes all names if they are
/// preserved.
@ -690,6 +702,13 @@ AllocaSlices::AllocaSlices(const DataLayout &DL, AllocaInst &AI)
std::mem_fun_ref(&Slice::isDead)),
Slices.end());
#if __cplusplus >= 201103L && !defined(NDEBUG)
if (SROARandomShuffleSlices) {
std::mt19937 MT(static_cast<unsigned>(sys::TimeValue::now().msec()));
std::shuffle(Slices.begin(), Slices.end(), MT);
}
#endif
// Sort the uses. This arranges for the offsets to be in ascending order,
// and the sizes to be in descending order.
std::sort(Slices.begin(), Slices.end());