From 8dab0a4a7d691f2704f1079538e0ef29548db159 Mon Sep 17 00:00:00 2001 From: Roman Lebedev Date: Fri, 3 Jan 2020 12:50:00 +0300 Subject: [DAGCombine][X86][AArch64] 'A - (A & (B - 1))' -> 'A & (0 - B)' fold (PR44448) While we do manage to fold integer-typed IR in middle-end, we can't do that for the main motivational case of pointers. There is @llvm.ptrmask() intrinsic which may or may not be helpful, but i'm not sure it is fully considered canonical yet, not everything is fully aware of it likely. https://rise4fun.com/Alive/ZVdp Name: ptr - (ptr & (alignment-1)) -> ptr & (0 - alignment) %mask = add i64 %alignment, -1 %bias = and i64 %ptr, %mask %r = sub i64 %ptr, %bias => %highbitmask = sub i64 0, %alignment %r = and i64 %ptr, %highbitmask See https://bugs.llvm.org/show_bug.cgi?id=44448 https://reviews.llvm.org/D71499 --- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'llvm/lib/CodeGen') diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 1415b1e37d1..5dbe29f5fbd 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -3104,6 +3104,21 @@ SDValue DAGCombiner::visitSUB(SDNode *N) { DAG.getNode(ISD::SUB, DL, VT, N1.getOperand(1), N1.getOperand(0))); + // A - (A & (B - 1)) -> A & (0 - B) + if (N1.getOpcode() == ISD::AND && N1.hasOneUse()) { + SDValue A = N1.getOperand(0); + SDValue BDec = N1.getOperand(1); + if (A != N0) + std::swap(A, BDec); + if (A == N0 && BDec.getOpcode() == ISD::ADD && + isAllOnesOrAllOnesSplat(BDec->getOperand(1))) { + SDValue B = BDec.getOperand(0); + SDValue NegB = + DAG.getNode(ISD::SUB, DL, VT, DAG.getConstant(0, DL, VT), B); + return DAG.getNode(ISD::AND, DL, VT, A, NegB); + } + } + // fold (X - (-Y * Z)) -> (X + (Y * Z)) if (N1.getOpcode() == ISD::MUL && N1.hasOneUse()) { if (N1.getOperand(0).getOpcode() == ISD::SUB && -- cgit v1.2.3