-//===- DivRemPairs.cpp - Hoist/[dr]ecompose division and remainder --------===//
+//===- DivRemPairs.cpp - Hoist/decompose division and remainder -*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
//
//===----------------------------------------------------------------------===//
//
-// This pass hoists and/or decomposes/recomposes integer division and remainder
+// This pass hoists and/or decomposes integer division and remainder
// instructions to enable CFG improvements and better codegen.
//
//===----------------------------------------------------------------------===//
#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<Instruction *, 1, bool /*Expanded*/>;
-
-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<ExpandedMatch> 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
DenseMap<DivRemMapKey, Instruction *> DivMap;
// Use a MapVector for RemMap so that instructions are moved/inserted in a
// deterministic order.
- MapVector<DivRemMapKey, InstructionWithInfo> RemMap;
+ MapVector<DivRemMapKey, Instruction *> RemMap;
for (auto &BB : F) {
for (auto &I : BB) {
if (I.getOpcode() == Instruction::SDiv)
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, /*Expanded=*/false};
+ RemMap[DivRemMapKey(true, I.getOperand(0), I.getOperand(1))] = &I;
else if (I.getOpcode() == Instruction::URem)
- RemMap[DivRemMapKey(false, I.getOperand(0), I.getOperand(1))] = {
- &I, /*Expanded=*/false};
- else if (auto Match = matchExpandedRem(I))
- RemMap[Match->Key] = Match->Value;
+ RemMap[DivRemMapKey(false, I.getOperand(0), I.getOperand(1))] = &I;
}
}
if (!DivInst)
continue;
- // 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.
+ // We have a matching pair of div/rem instructions. If one dominates the
+ // other, hoist and/or replace one.
NumPairs++;
- InstructionWithInfo RemLike = RemPair.second;
- // NOTE: RemInst may be in expanded form!
- Instruction *RemInst = RemLike.getPointer();
- bool IsInExpandedForm = RemLike.getInt();
- bool IsSigned = RemPair.first.SignedOp;
+ Instruction *RemInst = RemPair.second;
+ bool IsSigned = DivInst->getOpcode() == Instruction::SDiv;
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.
continue;
bool DivDominates = DT.dominates(DivInst, RemInst);
- 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?
+ if (!DivDominates && !DT.dominates(RemInst, DivInst))
continue;
- }
- // The target does not have a single div/rem operation,
- // and the rem is already in expanded form. Nothing to do.
- if (!HasDivRemOp && IsInExpandedForm)
+ if (!DebugCounter::shouldExecute(DRPCounter))
continue;
if (HasDivRemOp) {
DivInst->moveAfter(RemInst);
NumHoisted++;
} else {
- // 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:
+ // The target does not have a single div/rem operation. Decompose the
+ // remainder calculation as:
// X % Y --> X - ((X / Y) * Y).
Value *X = RemInst->getOperand(0);
Value *Y = RemInst->getOperand(1);
; CHECK-LABEL: @decompose_illegal_srem_same_block(
; CHECK-NEXT: [[DIV:%.*]] = sdiv i32 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[T0:%.*]] = mul i32 [[DIV]], [[B]]
-; CHECK-NEXT: [[REM:%.*]] = srem i32 [[A]], [[B]]
+; CHECK-NEXT: [[REM:%.*]] = sub i32 [[A]], [[T0]]
; CHECK-NEXT: call void @foo(i32 [[REM]], i32 [[DIV]])
; CHECK-NEXT: ret void
;
; CHECK-LABEL: @decompose_illegal_urem_same_block(
; CHECK-NEXT: [[DIV:%.*]] = udiv i32 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[T0:%.*]] = mul i32 [[DIV]], [[B]]
-; CHECK-NEXT: [[REM:%.*]] = urem i32 [[A]], [[B]]
+; CHECK-NEXT: [[REM:%.*]] = sub i32 [[A]], [[T0]]
; CHECK-NEXT: call void @foo(i32 [[REM]], i32 [[DIV]])
; CHECK-NEXT: ret void
;
; 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:%.*]] ]
; 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:%.*]] ]
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