https://bugs.llvm.org/show_bug.cgi?id=46983
Bug ID: 46983
Summary: [SLP] Failure to account for truncating stores in
MinVF calculation
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: a.bat...@hotmail.com, anton.a.afanas...@gmail.com,
llvm-bugs@lists.llvm.org
Blocks: 46968
Noticed while investigating [Bug #46968]
https://godbolt.org/z/T9Mna8
The MinVF calculation in SLPVectorizerPass::vectorizeStoreChain is based off
the
number of storesize elements that fix in the vector register:
const unsigned MinVF = R.getMinVecRegSize() / Sz;
But this means we fail to account for cases where we are truncating the result
just prior to the store.
Sz is set by:
unsigned BoUpSLP::getVectorElementSize(Value *V) {
// If V is a store, just return the width of the stored value without
// traversing the expression tree. This is the common case.
if (auto *Store = dyn_cast<StoreInst>(V))
return DL->getTypeSizeInBits(Store->getValueOperand()->getType());
...
}
So we may be able to just check for truncates feeding stores in the StoreInst
case.
Referenced Bugs:
https://bugs.llvm.org/show_bug.cgi?id=46968
[Bug 46968] Missed SLP vectorization with umin/umax
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