RPCS3/llvm
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm.git synced 2024-12-20 19:20:23 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Restrict LDA to GEPs with the same pointer offset.

Browse Source 
We can not simply apply ZIV testing to the pointer offsets, as this
would incorrectly return independence for e.g. (GEP x,0,i; GEP x,1,-i).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78155 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andreas Bolka 2009-08-05 04:13:41 +00:00
parent d250329291
commit a1b78d133e
1 changed files with 27 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

38
lib/Analysis/LoopDependenceAnalysis.cpp
View File

@ -195,28 +195,44 @@ LoopDependenceAnalysis::analysePair(DependencePair *P) const {
// FIXME: Is filtering coupled subscripts necessary?
// Analyse indices pairwise (FIXME: use GetGEPOperands from BasicAA), adding
// Collect GEP operand pairs (FIXME: use GetGEPOperands from BasicAA), adding
// trailing zeroes to the smaller GEP, if needed.
GEPOperator::const_op_iterator aIdx = aGEP->idx_begin(),
aEnd = aGEP->idx_end(),
bIdx = bGEP->idx_begin(),
bEnd = bGEP->idx_end();
while (aIdx != aEnd && bIdx != bEnd) {
typedef SmallVector<std::pair<const SCEV*, const SCEV*>, 4> GEPOpdPairsTy;
GEPOpdPairsTy opds;
for(GEPOperator::const_op_iterator aIdx = aGEP->idx_begin(),
aEnd = aGEP->idx_end(),
bIdx = bGEP->idx_begin(),
bEnd = bGEP->idx_end();
aIdx != aEnd && bIdx != bEnd;
aIdx += (aIdx != aEnd), bIdx += (bIdx != bEnd)) {
const SCEV* aSCEV = (aIdx != aEnd) ? SE->getSCEV(*aIdx) : GetZeroSCEV(SE);
const SCEV* bSCEV = (bIdx != bEnd) ? SE->getSCEV(*bIdx) : GetZeroSCEV(SE);
opds.push_back(std::make_pair(aSCEV, bSCEV));
}
if (!opds.empty() && opds[0].first != opds[0].second) {
// We cannot (yet) handle arbitrary GEP pointer offsets. By limiting
//
// TODO: this could be relaxed by adding the size of the underlying object
// to the first subscript. If we have e.g. (GEP x,0,i; GEP x,2,-i) and we
// know that x is a [100 x i8]*, we could modify the first subscript to be
// (i, 200-i) instead of (i, -i).
return Unknown;
}
// Now analyse the collected operand pairs (skipping the GEP ptr offsets).
for (GEPOpdPairsTy::const_iterator i = opds.begin() + 1, end = opds.end();
i != end; ++i) {
Subscript subscript;
DependenceResult result = analyseSubscript(aSCEV, bSCEV, &subscript);
DependenceResult result = analyseSubscript(i->first, i->second, &subscript);
if (result != Dependent) {
// We either proved independence or failed to analyse this subscript.
// Further subscripts will not improve the situation, so abort early.
return result;
}
P->Subscripts.push_back(subscript);
if (aIdx != aEnd) ++aIdx;
if (bIdx != bEnd) ++bIdx;
}
// Either there were no subscripts or all subscripts were analysed to be
// dependent; in both cases we know the accesses are dependent.
// We successfully analysed all subscripts but failed to prove independence.
return Dependent;
}