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Made SCEV's UDiv expressions more canonical. When dividing a

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recurrence, the initial values low bits can sometimes be ignored.

To take advantage of this, added FoldIVUser to IndVarSimplify to fold
an IV operand into a udiv/lshr if the operator doesn't affect the
result.

-indvars -disable-iv-rewrite now transforms

i = phi i4
i1 = i0 + 1
idx = i1 >> (2 or more)
i4 = i + 4

into

i = phi i4
idx = i0 >> ...
i4 = i + 4


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137013 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2011-08-06 07:00:37 +00:00
parent ccfa446450
commit 06988bcf6a
3 changed files with 142 additions and 4 deletions
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25
lib/Analysis/ScalarEvolution.cpp
View File

@ -2051,12 +2051,13 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
++MaxShiftAmt;
IntegerType *ExtTy =
IntegerType::get(getContext(), getTypeSizeInBits(Ty) + MaxShiftAmt);
// {X,+,N}/C --> {X/C,+,N/C} if safe and N/C can be folded.
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(LHS))
if (const SCEVConstant *Step =
dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this)))
if (!Step->getValue()->getValue()
.urem(RHSC->getValue()->getValue()) &&
dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this))) {
// {X,+,N}/C --> {X/C,+,N/C} if safe and N/C can be folded.
const APInt &StepInt = Step->getValue()->getValue();
const APInt &DivInt = RHSC->getValue()->getValue();
if (!StepInt.urem(DivInt) &&
getZeroExtendExpr(AR, ExtTy) ==
getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
getZeroExtendExpr(Step, ExtTy),
@ -2067,6 +2068,22 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
return getAddRecExpr(Operands, AR->getLoop(),
SCEV::FlagNW);
}
/// Get a canonical UDivExpr for a recurrence.
/// {X,+,N}/C => {Y,+,N}/C where Y=X-(X%N). Safe when C%N=0.
// We can currently only fold X%N if X is constant.
const SCEVConstant *StartC = dyn_cast<SCEVConstant>(AR->getStart());
if (StartC && !DivInt.urem(StepInt) &&
getZeroExtendExpr(AR, ExtTy) ==
getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
getZeroExtendExpr(Step, ExtTy),
AR->getLoop(), SCEV::FlagAnyWrap)) {
const APInt &StartInt = StartC->getValue()->getValue();
const APInt &StartRem = StartInt.urem(StepInt);
if (StartRem != 0)
LHS = getAddRecExpr(getConstant(StartInt - StartRem), Step,
AR->getLoop(), SCEV::FlagNW);
}
}
// (A*B)/C --> A*(B/C) if safe and B/C can be folded.
if (const SCEVMulExpr *M = dyn_cast<SCEVMulExpr>(LHS)) {
SmallVector<const SCEV *, 4> Operands;

65
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -70,6 +70,7 @@ STATISTIC(NumInserted , "Number of canonical indvars added");
STATISTIC(NumReplaced , "Number of exit values replaced");
STATISTIC(NumLFTR , "Number of loop exit tests replaced");
STATISTIC(NumElimIdentity, "Number of IV identities eliminated");
STATISTIC(NumElimOperand, "Number of IV operands folded into a use");
STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated");
STATISTIC(NumElimRem , "Number of IV remainder operations eliminated");
STATISTIC(NumElimCmp , "Number of IV comparisons eliminated");
@ -142,6 +143,8 @@ namespace {
Value *IVOperand,
bool IsSigned);
bool FoldIVUser(Instruction *UseInst, Instruction *IVOperand);
void SimplifyCongruentIVs(Loop *L);
void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter);
@ -1298,6 +1301,66 @@ bool IndVarSimplify::EliminateIVUser(Instruction *UseInst,
return true;
}
/// FoldIVUser - Fold an IV operand into its use. This removes increments of an
/// aligned IV when used by a instruction that ignores the low bits.
bool IndVarSimplify::FoldIVUser(Instruction *UseInst, Instruction *IVOperand) {
Value *IVSrc = 0;
unsigned OperIdx = 0;
const SCEV *FoldedExpr = 0;
switch (UseInst->getOpcode()) {
default:
return false;
case Instruction::UDiv:
case Instruction::LShr:
// We're only interested in the case where we know something about
// the numerator and have a constant denominator.
if (IVOperand != UseInst->getOperand(OperIdx) ||
!isa<ConstantInt>(UseInst->getOperand(1)))
return false;
// Attempt to fold a binary operator with constant operand.
// e.g. ((I + 1) >> 2) => I >> 2
if (IVOperand->getNumOperands() != 2 ||
!isa<ConstantInt>(IVOperand->getOperand(1)))
return false;
IVSrc = IVOperand->getOperand(0);
// IVSrc must be the (SCEVable) IV, since the other operand is const.
assert(SE->isSCEVable(IVSrc->getType()) && "Expect SCEVable IV operand");
ConstantInt *D = cast<ConstantInt>(UseInst->getOperand(1));
if (UseInst->getOpcode() == Instruction::LShr) {
// Get a constant for the divisor. See createSCEV.
uint32_t BitWidth = cast<IntegerType>(UseInst->getType())->getBitWidth();
if (D->getValue().uge(BitWidth))
return false;
D = ConstantInt::get(UseInst->getContext(),
APInt(BitWidth, 1).shl(D->getZExtValue()));
}
FoldedExpr = SE->getUDivExpr(SE->getSCEV(IVSrc), SE->getSCEV(D));
}
// We have something that might fold it's operand. Compare SCEVs.
if (!SE->isSCEVable(UseInst->getType()))
return false;
// Bypass the operand if SCEV can prove it has no effect.
if (SE->getSCEV(UseInst) != FoldedExpr)
return false;
DEBUG(dbgs() << "INDVARS: Eliminated IV operand: " << *IVOperand
<< " -> " << *UseInst << '\n');
UseInst->setOperand(OperIdx, IVSrc);
assert(SE->getSCEV(UseInst) == FoldedExpr && "bad SCEV with folded oper");
++NumElimOperand;
Changed = true;
if (IVOperand->use_empty())
DeadInsts.push_back(IVOperand);
return true;
}
/// pushIVUsers - Add all uses of Def to the current IV's worklist.
///
static void pushIVUsers(
@ -1394,6 +1457,8 @@ void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) {
// Bypass back edges to avoid extra work.
if (UseOper.first == CurrIV) continue;
FoldIVUser(UseOper.first, UseOper.second);
if (EliminateIVUser(UseOper.first, UseOper.second)) {
pushIVUsers(UseOper.second, Simplified, SimpleIVUsers);
continue;

56
test/Transforms/IndVarSimplify/iv-fold.ll Normal file
View File

@ -0,0 +1,56 @@
; RUN: opt < %s -indvars -disable-iv-rewrite -S | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n:32:64"
; Indvars should be able to fold IV increments into shr when low bits are zero.
;
; CHECK: @foldIncShr
; CHECK: shr.1 = lshr i32 %0, 5
define i32 @foldIncShr(i32* %bitmap, i32 %bit_addr, i32 %nbits) nounwind {
entry:
br label %while.body
while.body:
%0 = phi i32 [ 0, %entry ], [ %inc.2, %while.body ]
%shr = lshr i32 %0, 5
%arrayidx = getelementptr inbounds i32* %bitmap, i32 %shr
%tmp6 = load i32* %arrayidx, align 4
%inc.1 = add i32 %0, 1
%shr.1 = lshr i32 %inc.1, 5
%arrayidx.1 = getelementptr inbounds i32* %bitmap, i32 %shr.1
%tmp6.1 = load i32* %arrayidx.1, align 4
%inc.2 = add i32 %inc.1, 1
%exitcond.3 = icmp eq i32 %inc.2, 128
br i1 %exitcond.3, label %while.end, label %while.body
while.end:
%r = add i32 %tmp6, %tmp6.1
ret i32 %r
}
; Invdars should not fold an increment into shr unless 2^shiftBits is
; a multiple of the recurrence step.
;
; CHECK: @noFoldIncShr
; CHECK: shr.1 = lshr i32 %inc.1, 5
define i32 @noFoldIncShr(i32* %bitmap, i32 %bit_addr, i32 %nbits) nounwind {
entry:
br label %while.body
while.body:
%0 = phi i32 [ 0, %entry ], [ %inc.3, %while.body ]
%shr = lshr i32 %0, 5
%arrayidx = getelementptr inbounds i32* %bitmap, i32 %shr
%tmp6 = load i32* %arrayidx, align 4
%inc.1 = add i32 %0, 1
%shr.1 = lshr i32 %inc.1, 5
%arrayidx.1 = getelementptr inbounds i32* %bitmap, i32 %shr.1
%tmp6.1 = load i32* %arrayidx.1, align 4
%inc.3 = add i32 %inc.1, 2
%exitcond.3 = icmp eq i32 %inc.3, 96
br i1 %exitcond.3, label %while.end, label %while.body
while.end:
%r = add i32 %tmp6, %tmp6.1
ret i32 %r
}