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[SROA] Add an off-by-default *strict* inbounds check to SROA. I had SROA

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implemented this way a long time ago and due to the overwhelming bugs
that surfaced, moved to a much more relaxed variant. Richard Smith would
like to understand the magnitude of this problem and it seems fairly
harmless to keep some flag-controlled logic to get the extremely strict
behavior here. I'll remove it if it doesn't prove useful.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202193 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2014-02-25 21:24:45 +00:00
parent 15ac7dfb90
commit 495e40121b
1 changed files with 42 additions and 0 deletions
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42
lib/Transforms/Scalar/SROA.cpp
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@ -85,6 +85,11 @@ ForceSSAUpdater("force-ssa-updater", cl::init(false), cl::Hidden);
static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices", static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices",
cl::init(false), cl::Hidden); cl::init(false), cl::Hidden);
/// Hidden option to experiment with completely strict handling of inbounds
/// GEPs.
static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds",
cl::init(false), cl::Hidden);
namespace { namespace {
/// \brief A custom IRBuilder inserter which prefixes all names if they are /// \brief A custom IRBuilder inserter which prefixes all names if they are
/// preserved. /// preserved.
@ -392,6 +397,43 @@ private:
if (GEPI.use_empty()) if (GEPI.use_empty())
return markAsDead(GEPI); return markAsDead(GEPI);
if (SROAStrictInbounds && GEPI.isInBounds()) {
// FIXME: This is a manually un-factored variant of the basic code inside
// of GEPs with checking of the inbounds invariant specified in the
// langref in a very strict sense. If we ever want to enable
// SROAStrictInbounds, this code should be factored cleanly into
// PtrUseVisitor, but it is easier to experiment with SROAStrictInbounds
// by writing out the code here where we have tho underlying allocation
// size readily available.
APInt GEPOffset = Offset;
for (gep_type_iterator GTI = gep_type_begin(GEPI),
GTE = gep_type_end(GEPI);
GTI != GTE; ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
if (!OpC)
break;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = dyn_cast<StructType>(*GTI)) {
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = DL.getStructLayout(STy);
GEPOffset +=
APInt(Offset.getBitWidth(), SL->getElementOffset(ElementIdx));
} else {
// For array or vector indices, scale the index by the size of the type.
APInt Index = OpC->getValue().sextOrTrunc(Offset.getBitWidth());
GEPOffset += Index * APInt(Offset.getBitWidth(),
DL.getTypeAllocSize(GTI.getIndexedType()));
}
// If this index has computed an intermediate pointer which is not
// inbounds, then the result of the GEP is a poison value and we can
// delete it and all uses.
if (GEPOffset.ugt(AllocSize))
return markAsDead(GEPI);
}
}
return Base::visitGetElementPtrInst(GEPI); return Base::visitGetElementPtrInst(GEPI);
} }