Add vector versions of some existing scalar transforms to aid codegen in matching psign & pblend operations to the IR produced by clang/gcc for their C idioms.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122105 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 79a9b09..df2abb5 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1020,6 +1020,23 @@
}
}
+ // vector (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed
+ if (const VectorType *VTy = dyn_cast<VectorType>(DestTy)) {
+ ICmpInst::Predicate Pred; Value *CmpLHS;
+ if (match(Src, m_ICmp(Pred, m_Value(CmpLHS), m_Zero()))) {
+ if (Pred == ICmpInst::ICMP_SLT && CmpLHS->getType() == DestTy) {
+ const Type *EltTy = VTy->getElementType();
+
+ // splat the shift constant to a cosntant vector
+ Constant *Sh = ConstantInt::get(EltTy, EltTy->getScalarSizeInBits()-1);
+ std::vector<Constant *> Elts(VTy->getNumElements(), Sh);
+ Constant *VSh = ConstantVector::get(Elts);
+
+ Value *In = Builder->CreateAShr(CmpLHS, VSh, CmpLHS->getName()+".lobit");
+ return ReplaceInstUsesWith(CI, In);
+ }
+ }
+ }
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth