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Teach IndVarSimplify how to eliminate remainder operators where the

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numerator is an induction variable. For example, with code like this:

  for (i=0;i<n;++i)
    x[i%n] = 0;

IndVarSimplify will now recognize that i is always less than n inside
the loop, and eliminate the remainder.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101113 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-04-13 01:46:36 +00:00
parent afc9a0c6b0
commit a590b79ee2
2 changed files with 192 additions and 0 deletions
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71
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -98,6 +98,7 @@ namespace {
private:
void EliminateIVComparisons();
void EliminateIVRemainders();
void RewriteNonIntegerIVs(Loop *L);
ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
@ -398,6 +399,73 @@ void IndVarSimplify::EliminateIVComparisons() {
RecursivelyDeleteTriviallyDeadInstructions(Inst);
}
void IndVarSimplify::EliminateIVRemainders() {
SmallVector<WeakVH, 16> DeadInsts;
// Look for SRem and URem users.
for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E; ++I) {
IVStrideUse &UI = *I;
BinaryOperator *Rem = dyn_cast<BinaryOperator>(UI.getUser());
if (!Rem) continue;
bool isSigned = Rem->getOpcode() == Instruction::SRem;
if (!isSigned && Rem->getOpcode() != Instruction::URem)
continue;
// We're only interested in the case where we know something about
// the numerator.
if (UI.getOperandValToReplace() != Rem->getOperand(0))
continue;
// Get the SCEVs for the ICmp operands.
const SCEV *S = SE->getSCEV(Rem->getOperand(0));
const SCEV *X = SE->getSCEV(Rem->getOperand(1));
// Simplify unnecessary loops away.
const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent());
S = SE->getSCEVAtScope(S, ICmpLoop);
X = SE->getSCEVAtScope(X, ICmpLoop);
// i % n --> i if i is in [0,n).
if ((!isSigned || SE->isKnownNonNegative(S)) &&
SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
S, X))
Rem->replaceAllUsesWith(Rem->getOperand(0));
else {
// (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n).
const SCEV *LessOne =
SE->getMinusSCEV(S, SE->getIntegerSCEV(1, S->getType()));
if ((!isSigned || SE->isKnownNonNegative(LessOne)) &&
SE->isKnownPredicate(isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
LessOne, X)) {
ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ,
Rem->getOperand(0), Rem->getOperand(1),
"tmp");
SelectInst *Sel =
SelectInst::Create(ICmp,
ConstantInt::get(Rem->getType(), 0),
Rem->getOperand(0), "tmp", Rem);
Rem->replaceAllUsesWith(Sel);
} else
continue;
}
// Inform IVUsers about the new users.
if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0)))
IU->AddUsersIfInteresting(I);
DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n');
DeadInsts.push_back(Rem);
}
// Now that we're done iterating through lists, clean up any instructions
// which are now dead.
while (!DeadInsts.empty())
if (Instruction *Inst =
dyn_cast_or_null<Instruction>(DeadInsts.pop_back_val()))
RecursivelyDeleteTriviallyDeadInstructions(Inst);
}
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
IU = &getAnalysis<IVUsers>();
LI = &getAnalysis<LoopInfo>();
@ -427,6 +495,9 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
// Simplify ICmp IV users.
EliminateIVComparisons();
// Simplify SRem and URem IV users.
EliminateIVRemainders();
// Compute the type of the largest recurrence expression, and decide whether
// a canonical induction variable should be inserted.
const Type *LargestType = 0;

121
test/Transforms/IndVarSimplify/eliminate-rem.ll Normal file
View File

@ -0,0 +1,121 @@
; RUN: opt -indvars -S < %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-n8:16:32:64"
; Indvars should be able to eliminate this srem.
; CHECK: @simple
; CHECK-NOT: rem
; CHECK: ret
define void @simple(i64 %arg, double* %arg3) nounwind {
bb:
%t = icmp slt i64 0, %arg ; <i1> [#uses=1]
br i1 %t, label %bb4, label %bb12
bb4: ; preds = %bb
br label %bb5
bb5: ; preds = %bb4, %bb5
%t6 = phi i64 [ %t9, %bb5 ], [ 0, %bb4 ] ; <i64> [#uses=2]
%t7 = srem i64 %t6, %arg ; <i64> [#uses=1]
%t8 = getelementptr inbounds double* %arg3, i64 %t7 ; <double*> [#uses=1]
store double 0.000000e+00, double* %t8
%t9 = add nsw i64 %t6, 1 ; <i64> [#uses=2]
%t10 = icmp slt i64 %t9, %arg ; <i1> [#uses=1]
br i1 %t10, label %bb5, label %bb11
bb11: ; preds = %bb5
br label %bb12
bb12: ; preds = %bb11, %bb
ret void
}
; Indvars should be able to eliminate the (i+1)%n.
; CHECK: @f
; CHECK-NOT: rem
; CHECK: rem
; CHECK-NOT: rem
; CHECK: ret
define i32 @f(i64* %arg, i64 %arg1, i64 %arg2, i64 %arg3) nounwind {
bb:
%t = icmp sgt i64 %arg1, 0 ; <i1> [#uses=1]
br i1 %t, label %bb4, label %bb54
bb4: ; preds = %bb
br label %bb5
bb5: ; preds = %bb49, %bb4
%t6 = phi i64 [ %t51, %bb49 ], [ 0, %bb4 ] ; <i64> [#uses=4]
%t7 = phi i32 [ %t50, %bb49 ], [ 0, %bb4 ] ; <i32> [#uses=2]
%t8 = add nsw i64 %t6, %arg1 ; <i64> [#uses=1]
%t9 = add nsw i64 %t8, -2 ; <i64> [#uses=1]
%t10 = srem i64 %t9, %arg1 ; <i64> [#uses=1]
%t11 = add nsw i64 %t10, 1 ; <i64> [#uses=1]
%t12 = add nsw i64 %t6, 1 ; <i64> [#uses=1]
%t13 = srem i64 %t12, %arg1 ; <i64> [#uses=1]
%t14 = icmp sgt i64 %arg1, 0 ; <i1> [#uses=1]
br i1 %t14, label %bb15, label %bb49
bb15: ; preds = %bb5
br label %bb16
bb16: ; preds = %bb44, %bb15
%t17 = phi i64 [ %t46, %bb44 ], [ 0, %bb15 ] ; <i64> [#uses=1]
%t18 = phi i32 [ %t45, %bb44 ], [ %t7, %bb15 ] ; <i32> [#uses=2]
%t19 = icmp sgt i64 %arg1, 0 ; <i1> [#uses=1]
br i1 %t19, label %bb20, label %bb44
bb20: ; preds = %bb16
br label %bb21
bb21: ; preds = %bb21, %bb20
%t22 = phi i64 [ %t41, %bb21 ], [ 0, %bb20 ] ; <i64> [#uses=4]
%t23 = phi i32 [ %t40, %bb21 ], [ %t18, %bb20 ] ; <i32> [#uses=1]
%t24 = mul i64 %t6, %arg1 ; <i64> [#uses=1]
%t25 = mul i64 %t13, %arg1 ; <i64> [#uses=1]
%t26 = add nsw i64 %t24, %t22 ; <i64> [#uses=1]
%t27 = mul i64 %t11, %arg1 ; <i64> [#uses=1]
%t28 = add nsw i64 %t25, %t22 ; <i64> [#uses=1]
%t29 = getelementptr inbounds i64* %arg, i64 %t26 ; <i64*> [#uses=1]
%t30 = add nsw i64 %t27, %t22 ; <i64> [#uses=1]
%t31 = getelementptr inbounds i64* %arg, i64 %t28 ; <i64*> [#uses=1]
%t32 = zext i32 %t23 to i64 ; <i64> [#uses=1]
%t33 = load i64* %t29 ; <i64> [#uses=1]
%t34 = getelementptr inbounds i64* %arg, i64 %t30 ; <i64*> [#uses=1]
%t35 = load i64* %t31 ; <i64> [#uses=1]
%t36 = add nsw i64 %t32, %t33 ; <i64> [#uses=1]
%t37 = add nsw i64 %t36, %t35 ; <i64> [#uses=1]
%t38 = load i64* %t34 ; <i64> [#uses=1]
%t39 = add nsw i64 %t37, %t38 ; <i64> [#uses=1]
%t40 = trunc i64 %t39 to i32 ; <i32> [#uses=2]
%t41 = add nsw i64 %t22, 1 ; <i64> [#uses=2]
%t42 = icmp slt i64 %t41, %arg1 ; <i1> [#uses=1]
br i1 %t42, label %bb21, label %bb43
bb43: ; preds = %bb21
br label %bb44
bb44: ; preds = %bb43, %bb16
%t45 = phi i32 [ %t18, %bb16 ], [ %t40, %bb43 ] ; <i32> [#uses=2]
%t46 = add nsw i64 %t17, 1 ; <i64> [#uses=2]
%t47 = icmp slt i64 %t46, %arg1 ; <i1> [#uses=1]
br i1 %t47, label %bb16, label %bb48
bb48: ; preds = %bb44
br label %bb49
bb49: ; preds = %bb48, %bb5
%t50 = phi i32 [ %t7, %bb5 ], [ %t45, %bb48 ] ; <i32> [#uses=2]
%t51 = add nsw i64 %t6, 1 ; <i64> [#uses=2]
%t52 = icmp slt i64 %t51, %arg1 ; <i1> [#uses=1]
br i1 %t52, label %bb5, label %bb53
bb53: ; preds = %bb49
br label %bb54
bb54: ; preds = %bb53, %bb
%t55 = phi i32 [ 0, %bb ], [ %t50, %bb53 ] ; <i32> [#uses=1]
ret i32 %t55
}