[InstCombine, ARM, AArch64] Convert table lookup to shuffle vector
Turning a table lookup intrinsic into a shuffle vector instruction
can be beneficial. If the mask used for the lookup is the constant
vector {7,6,5,4,3,2,1,0}, then the back-end generates byte reverse
instructions instead.
Differential Revision: https://reviews.llvm.org/D46133
llvm-svn: 333550
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index a5a0edc..7fbf068 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1387,6 +1387,46 @@
return maxnum(Src0, Src1);
}
+/// Convert a table lookup to shufflevector if the mask is constant.
+/// This could benefit tbl1 if the mask is { 7,6,5,4,3,2,1,0 }, in
+/// which case we could lower the shufflevector with rev64 instructions
+/// as it's actually a byte reverse.
+static Value *simplifyNeonTbl1(const IntrinsicInst &II,
+ InstCombiner::BuilderTy &Builder) {
+ // Bail out if the mask is not a constant.
+ auto *C = dyn_cast<Constant>(II.getArgOperand(1));
+ if (!C)
+ return nullptr;
+
+ auto *VecTy = cast<VectorType>(II.getType());
+ unsigned NumElts = VecTy->getNumElements();
+
+ // Only perform this transformation for <8 x i8> vector types.
+ if (!VecTy->getElementType()->isIntegerTy(8) || NumElts != 8)
+ return nullptr;
+
+ uint32_t Indexes[8];
+
+ for (unsigned I = 0; I < NumElts; ++I) {
+ Constant *COp = C->getAggregateElement(I);
+
+ if (!COp || !isa<ConstantInt>(COp))
+ return nullptr;
+
+ Indexes[I] = cast<ConstantInt>(COp)->getLimitedValue();
+
+ // Make sure the mask indices are in range.
+ if (Indexes[I] >= NumElts)
+ return nullptr;
+ }
+
+ auto *ShuffleMask = ConstantDataVector::get(II.getContext(),
+ makeArrayRef(Indexes));
+ auto *V1 = II.getArgOperand(0);
+ auto *V2 = Constant::getNullValue(V1->getType());
+ return Builder.CreateShuffleVector(V1, V2, ShuffleMask);
+}
+
// Returns true iff the 2 intrinsics have the same operands, limiting the
// comparison to the first NumOperands.
static bool haveSameOperands(const IntrinsicInst &I, const IntrinsicInst &E,
@@ -2928,6 +2968,12 @@
break;
}
+ case Intrinsic::arm_neon_vtbl1:
+ case Intrinsic::aarch64_neon_tbl1:
+ if (Value *V = simplifyNeonTbl1(*II, Builder))
+ return replaceInstUsesWith(*II, V);
+ break;
+
case Intrinsic::arm_neon_vmulls:
case Intrinsic::arm_neon_vmullu:
case Intrinsic::aarch64_neon_smull: