Index: llvm/trunk/include/llvm/Transforms/Utils/BypassSlowDivision.h =================================================================== --- llvm/trunk/include/llvm/Transforms/Utils/BypassSlowDivision.h +++ llvm/trunk/include/llvm/Transforms/Utils/BypassSlowDivision.h @@ -31,6 +31,8 @@ Value *Dividend; Value *Divisor; + DivRemMapKey() = default; + DivRemMapKey(bool InSignedOp, Value *InDividend, Value *InDivisor) : SignedOp(InSignedOp), Dividend(InDividend), Divisor(InDivisor) {} }; Index: llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp =================================================================== --- llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp +++ llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp @@ -1,4 +1,4 @@ -//===- DivRemPairs.cpp - Hoist/decompose division and remainder -*- C++ -*-===// +//===- DivRemPairs.cpp - Hoist/[dr]ecompose division and remainder --------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. @@ -6,7 +6,7 @@ // //===----------------------------------------------------------------------===// // -// This pass hoists and/or decomposes integer division and remainder +// This pass hoists and/or decomposes/recomposes integer division and remainder // instructions to enable CFG improvements and better codegen. // //===----------------------------------------------------------------------===// @@ -19,19 +19,59 @@ #include "llvm/Analysis/TargetTransformInfo.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" +#include "llvm/IR/PatternMatch.h" #include "llvm/Pass.h" #include "llvm/Support/DebugCounter.h" #include "llvm/Transforms/Scalar.h" #include "llvm/Transforms/Utils/BypassSlowDivision.h" + using namespace llvm; +using namespace llvm::PatternMatch; #define DEBUG_TYPE "div-rem-pairs" STATISTIC(NumPairs, "Number of div/rem pairs"); +STATISTIC(NumRecomposed, "Number of instructions recomposed"); STATISTIC(NumHoisted, "Number of instructions hoisted"); STATISTIC(NumDecomposed, "Number of instructions decomposed"); DEBUG_COUNTER(DRPCounter, "div-rem-pairs-transform", "Controls transformations in div-rem-pairs pass"); +namespace { +using InstructionWithInfo = PointerIntPair; + +struct ExpandedMatch { + DivRemMapKey Key; + InstructionWithInfo Value; +}; +} // namespace + +/// See if we can match: (which is the form we expand into) +/// X - ((X ?/ Y) * Y) +/// which is equivalent to: +/// X ?% Y +static llvm::Optional matchExpandedRem(Instruction &I) { + ExpandedMatch M; + M.Value.setPointer(&I); + M.Value.setInt(/*Expanded=*/true); + + Value *XroundedDownToMultipleOfY; + if (!match(&I, m_Sub(m_Value(M.Key.Dividend), + m_Value(XroundedDownToMultipleOfY)))) + return llvm::None; + + Instruction *Div; + // Look for ((X / Y) * Y) + if (!match(XroundedDownToMultipleOfY, + m_c_Mul(m_CombineAnd(m_IDiv(m_Specific(M.Key.Dividend), + m_Value(M.Key.Divisor)), + m_Instruction(Div)), + m_Deferred(M.Key.Divisor)))) + return llvm::None; + + M.Key.SignedOp = Div->getOpcode() == Instruction::SDiv; + return M; +} + /// Find matching pairs of integer div/rem ops (they have the same numerator, /// denominator, and signedness). If they exist in different basic blocks, bring /// them together by hoisting or replace the common division operation that is @@ -55,7 +95,7 @@ DenseMap DivMap; // Use a MapVector for RemMap so that instructions are moved/inserted in a // deterministic order. - MapVector RemMap; + MapVector RemMap; for (auto &BB : F) { for (auto &I : BB) { if (I.getOpcode() == Instruction::SDiv) @@ -63,9 +103,13 @@ else if (I.getOpcode() == Instruction::UDiv) DivMap[DivRemMapKey(false, I.getOperand(0), I.getOperand(1))] = &I; else if (I.getOpcode() == Instruction::SRem) - RemMap[DivRemMapKey(true, I.getOperand(0), I.getOperand(1))] = &I; + RemMap[DivRemMapKey(true, I.getOperand(0), I.getOperand(1))] = { + &I, /*Expanded=*/false}; else if (I.getOpcode() == Instruction::URem) - RemMap[DivRemMapKey(false, I.getOperand(0), I.getOperand(1))] = &I; + RemMap[DivRemMapKey(false, I.getOperand(0), I.getOperand(1))] = { + &I, /*Expanded=*/false}; + else if (auto Match = matchExpandedRem(I)) + RemMap[Match->Key] = Match->Value; } } @@ -78,13 +122,45 @@ if (!DivInst) continue; - // We have a matching pair of div/rem instructions. If one dominates the - // other, hoist and/or replace one. + // We have a matching pair of div/rem instructions. + // If the rem is in expanded form, collapse it into rem first. + // If one dominates the other, hoist and/or replace one. NumPairs++; - Instruction *RemInst = RemPair.second; - bool IsSigned = DivInst->getOpcode() == Instruction::SDiv; + InstructionWithInfo RemLike = RemPair.second; + // NOTE: RemInst may be in expanded form! + Instruction *RemInst = RemLike.getPointer(); + bool IsInExpandedForm = RemLike.getInt(); + bool IsSigned = RemPair.first.SignedOp; bool HasDivRemOp = TTI.hasDivRemOp(DivInst->getType(), IsSigned); + if (!DebugCounter::shouldExecute(DRPCounter)) + continue; + + if (HasDivRemOp && IsInExpandedForm) { + // The target supports div+rem but the rem is expanded. + // We should recompose it first. + Value *X = RemPair.first.Dividend; + Value *Y = RemPair.first.Divisor; + Instruction *RealRem = IsSigned ? BinaryOperator::CreateSRem(X, Y) + : BinaryOperator::CreateURem(X, Y); + // Note that we place it right next to the original expanded instruction, + // and letting further handling to move it if needed. + RealRem->takeName(RemInst); + RealRem->insertAfter(RemInst); + RemInst->replaceAllUsesWith(RealRem); + RemInst->eraseFromParent(); + RemInst = RealRem; + NumRecomposed++; + // Note that we have left ((X / Y) * Y) around. + // If it had other uses we could rewrite it as X - X % Y + } + + assert(((RemInst->getOpcode() == Instruction::SRem || + RemInst->getOpcode() == Instruction::URem) || + !HasDivRemOp) && + "*If* the target supports div-rem, then by now the RemInst *is* " + "Instruction::[US]Rem."); + // If the target supports div+rem and the instructions are in the same block // already, there's nothing to do. The backend should handle this. If the // target does not support div+rem, then we will decompose the rem. @@ -92,10 +168,17 @@ continue; bool DivDominates = DT.dominates(DivInst, RemInst); - if (!DivDominates && !DT.dominates(RemInst, DivInst)) + if (!DivDominates && !DT.dominates(RemInst, DivInst)) { + // We have matching div-rem pair, but they are in two different blocks, + // neither of which dominates one another. + assert(!IsInExpandedForm && "Won't happen if matched expanded form."); + // FIXME: We could hoist both ops to the common predecessor block? continue; + } - if (!DebugCounter::shouldExecute(DRPCounter)) + // The target does not have a single div/rem operation, + // and the rem is already in expanded form. Nothing to do. + if (!HasDivRemOp && IsInExpandedForm) continue; if (HasDivRemOp) { @@ -107,8 +190,9 @@ DivInst->moveAfter(RemInst); NumHoisted++; } else { - // The target does not have a single div/rem operation. Decompose the - // remainder calculation as: + // The target does not have a single div/rem operation, + // and the rem is *not* in a already-expanded form. + // Decompose the remainder calculation as: // X % Y --> X - ((X / Y) * Y). Value *X = RemInst->getOperand(0); Value *Y = RemInst->getOperand(1); Index: llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll =================================================================== --- llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll +++ llvm/trunk/test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll @@ -7,7 +7,7 @@ ; CHECK-LABEL: @decompose_illegal_srem_same_block( ; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[A:%.*]], [[B:%.*]] ; CHECK-NEXT: [[T0:%.*]] = mul i32 [[DIV]], [[B]] -; CHECK-NEXT: [[REM:%.*]] = sub i32 [[A]], [[T0]] +; CHECK-NEXT: [[REM:%.*]] = srem i32 [[A]], [[B]] ; CHECK-NEXT: call void @foo(i32 [[REM]], i32 [[DIV]]) ; CHECK-NEXT: ret void ; @@ -22,7 +22,7 @@ ; CHECK-LABEL: @decompose_illegal_urem_same_block( ; CHECK-NEXT: [[DIV:%.*]] = udiv i32 [[A:%.*]], [[B:%.*]] ; CHECK-NEXT: [[T0:%.*]] = mul i32 [[DIV]], [[B]] -; CHECK-NEXT: [[REM:%.*]] = sub i32 [[A]], [[T0]] +; CHECK-NEXT: [[REM:%.*]] = urem i32 [[A]], [[B]] ; CHECK-NEXT: call void @foo(i32 [[REM]], i32 [[DIV]]) ; CHECK-NEXT: ret void ; @@ -39,11 +39,11 @@ ; CHECK-LABEL: @hoist_srem( ; CHECK-NEXT: entry: ; CHECK-NEXT: [[DIV:%.*]] = sdiv i16 [[A:%.*]], [[B:%.*]] +; CHECK-NEXT: [[REM:%.*]] = srem i16 [[A]], [[B]] ; CHECK-NEXT: [[CMP:%.*]] = icmp eq i16 [[DIV]], 42 ; CHECK-NEXT: br i1 [[CMP]], label [[IF:%.*]], label [[END:%.*]] ; CHECK: if: ; CHECK-NEXT: [[T0:%.*]] = mul i16 [[DIV]], [[B]] -; CHECK-NEXT: [[REM:%.*]] = sub i16 [[A]], [[T0]] ; CHECK-NEXT: br label [[END]] ; CHECK: end: ; CHECK-NEXT: [[RET:%.*]] = phi i16 [ [[REM]], [[IF]] ], [ 3, [[ENTRY:%.*]] ] @@ -70,11 +70,11 @@ ; CHECK-LABEL: @hoist_urem( ; CHECK-NEXT: entry: ; CHECK-NEXT: [[DIV:%.*]] = udiv i8 [[A:%.*]], [[B:%.*]] +; CHECK-NEXT: [[REM:%.*]] = urem i8 [[A]], [[B]] ; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[DIV]], 42 ; CHECK-NEXT: br i1 [[CMP]], label [[IF:%.*]], label [[END:%.*]] ; CHECK: if: ; CHECK-NEXT: [[T0:%.*]] = mul i8 [[DIV]], [[B]] -; CHECK-NEXT: [[REM:%.*]] = sub i8 [[A]], [[T0]] ; CHECK-NEXT: br label [[END]] ; CHECK: end: ; CHECK-NEXT: [[RET:%.*]] = phi i8 [ [[REM]], [[IF]] ], [ 3, [[ENTRY:%.*]] ]