[SLSR] consider &B[S << i] as &B[(1 << i) * S]
Summary: This reduces handling &B[(1 << i) * s] to handling &B[i * S].
Test Plan: slsr-gep.ll
Reviewers: meheff
Subscribers: sanjoy, llvm-commits
Differential Revision: http://reviews.llvm.org/D8837
llvm-svn: 234180
diff --git a/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
index d2eb0e9..681a70c 100644
--- a/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
@@ -353,8 +353,6 @@
ArrayIdx, ElementSize, GEP);
Value *LHS = nullptr;
ConstantInt *RHS = nullptr;
- // TODO: handle shl. e.g., we could treat (S << 2) as (S * 4).
- //
// One alternative is matching the SCEV of ArrayIdx instead of ArrayIdx
// itself. This would allow us to handle the shl case for free. However,
// matching SCEVs has two issues:
@@ -370,6 +368,13 @@
// SLSR is currently unsafe if i * S may overflow.
// GEP = Base + sext(LHS *nsw RHS) * ElementSize
allocateCandidateAndFindBasisForGEP(Base, RHS, LHS, ElementSize, GEP);
+ } else if (match(ArrayIdx, m_NSWShl(m_Value(LHS), m_ConstantInt(RHS)))) {
+ // GEP = Base + sext(LHS <<nsw RHS) * ElementSize
+ // = Base + sext(LHS *nsw (1 << RHS)) * ElementSize
+ APInt One(RHS->getBitWidth(), 1);
+ ConstantInt *PowerOf2 =
+ ConstantInt::get(RHS->getContext(), One << RHS->getValue());
+ allocateCandidateAndFindBasisForGEP(Base, PowerOf2, LHS, ElementSize, GEP);
}
}