[InstCombine] canonicalize insert+splat to/from element 0 of vector
We recognize a splat from element 0 in (VectorUtils) llvm::getSplatValue()
and also in ShuffleVectorInst::isZeroEltSplatMask(), so this converts
to that form for better matching.
The backend generically turns these patterns into build_vector,
so there should be no codegen difference.
llvm-svn: 365342
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 22d1e48..b928ae5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1346,6 +1346,41 @@
return NewBO;
}
+/// If we have an insert of a scalar to a non-zero element of an undefined
+/// vector and then shuffle that value, that's the same as inserting to the zero
+/// element and shuffling. Splatting from the zero element is recognized as the
+/// canonical form of splat.
+static Instruction *canonicalizeInsertSplat(ShuffleVectorInst &Shuf,
+ InstCombiner::BuilderTy &Builder) {
+ Value *Op0 = Shuf.getOperand(0), *Op1 = Shuf.getOperand(1);
+ Constant *Mask = Shuf.getMask();
+ Value *X;
+ uint64_t IndexC;
+
+ // Match a shuffle that is a splat to a non-zero element.
+ if (!match(Op0, m_OneUse(m_InsertElement(m_Undef(), m_Value(X),
+ m_ConstantInt(IndexC)))) ||
+ !match(Op1, m_Undef()) || match(Mask, m_ZeroInt()) || IndexC == 0)
+ return nullptr;
+
+ // Insert into element 0 of an undef vector.
+ UndefValue *UndefVec = UndefValue::get(Shuf.getType());
+ Constant *Zero = Builder.getInt32(0);
+ Value *NewIns = Builder.CreateInsertElement(UndefVec, X, Zero);
+
+ // Splat from element 0. Any mask element that is undefined remains undefined.
+ // For example:
+ // shuf (inselt undef, X, 2), undef, <2,2,undef>
+ // --> shuf (inselt undef, X, 0), undef, <0,0,undef>
+ unsigned NumMaskElts = Shuf.getType()->getVectorNumElements();
+ SmallVector<Constant *, 16> NewMask(NumMaskElts, Zero);
+ for (unsigned i = 0; i != NumMaskElts; ++i)
+ if (isa<UndefValue>(Mask->getAggregateElement(i)))
+ NewMask[i] = Mask->getAggregateElement(i);
+
+ return new ShuffleVectorInst(NewIns, UndefVec, ConstantVector::get(NewMask));
+}
+
/// Try to fold shuffles that are the equivalent of a vector select.
static Instruction *foldSelectShuffle(ShuffleVectorInst &Shuf,
InstCombiner::BuilderTy &Builder,
@@ -1714,6 +1749,9 @@
return &SVI;
}
+ if (Instruction *I = canonicalizeInsertSplat(SVI, Builder))
+ return I;
+
if (Instruction *I = foldSelectShuffle(SVI, Builder, DL))
return I;