forked from OSchip/llvm-project
[IndVars] Have `cloneArithmeticIVUser` guess better
Summary:
`cloneArithmeticIVUser` currently trips over expression like `add %iv,
-1` when `%iv` is being zero extended -- it tries to construct the
widened use as `add %iv.zext, zext(-1)` and (correctly) fails to prove
equivalence to `zext(add %iv, -1)` (here the SCEV for `%iv` is
`{1,+,1}`).
This change teaches `IndVars` to try sign extending the non-IV operand
if that makes the newly constructed IV use equivalent to the widened
narrow IV use.
Reviewers: atrick, hfinkel, reames
Subscribers: sanjoy, llvm-commits
Differential Revision: http://reviews.llvm.org/D13717
llvm-svn: 250483
This commit is contained in:
Sanjoy Das
parent
472840a3d3
commit
37e87c2023
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@ -998,22 +998,84 @@ Instruction *WidenIV::cloneArithmeticIVUser(NarrowIVDefUse DU,
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DEBUG(dbgs() << "Cloning arithmetic IVUser: " << *NarrowUse << "\n");
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// Replace NarrowDef operands with WideDef. Otherwise, we don't know anything
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// about the narrow operand yet so must insert a [sz]ext. It is probably loop
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// invariant and will be folded or hoisted. If it actually comes from a
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// widened IV, it should be removed during a future call to widenIVUse.
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Value *LHS =
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(NarrowUse->getOperand(0) == NarrowDef)
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? WideDef
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: getExtend(NarrowUse->getOperand(0), WideType, IsSigned, NarrowUse);
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Value *RHS =
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(NarrowUse->getOperand(1) == NarrowDef)
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? WideDef
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: getExtend(NarrowUse->getOperand(1), WideType, IsSigned, NarrowUse);
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unsigned IVOpIdx = (NarrowUse->getOperand(0) == NarrowDef) ? 0 : 1;
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// We're trying to find X such that
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//
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// Widen(NarrowDef `op` NonIVNarrowDef) == WideAR == WideDef `op.wide` X
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//
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// We guess two solutions to X, sext(NonIVNarrowDef) and zext(NonIVNarrowDef),
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// and check using SCEV if any of them are correct.
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// Returns true if extending NonIVNarrowDef according to `SignExt` is a
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// correct solution to X.
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auto GuessNonIVOperand = [&](bool SignExt) {
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const SCEV *WideLHS;
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const SCEV *WideRHS;
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auto GetExtend = [this, SignExt](const SCEV *S, Type *Ty) {
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if (SignExt)
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return SE->getSignExtendExpr(S, Ty);
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return SE->getZeroExtendExpr(S, Ty);
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};
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if (IVOpIdx == 0) {
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WideLHS = SE->getSCEV(WideDef);
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const SCEV *NarrowRHS = SE->getSCEV(NarrowUse->getOperand(1));
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WideRHS = GetExtend(NarrowRHS, WideType);
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} else {
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const SCEV *NarrowLHS = SE->getSCEV(NarrowUse->getOperand(0));
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WideLHS = GetExtend(NarrowLHS, WideType);
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WideRHS = SE->getSCEV(WideDef);
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}
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// WideUse is "WideDef `op.wide` X" as described in the comment.
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const SCEV *WideUse = nullptr;
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switch (NarrowUse->getOpcode()) {
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default:
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llvm_unreachable("No other possibility!");
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case Instruction::Add:
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WideUse = SE->getAddExpr(WideLHS, WideRHS);
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break;
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case Instruction::Mul:
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WideUse = SE->getMulExpr(WideLHS, WideRHS);
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break;
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case Instruction::UDiv:
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WideUse = SE->getUDivExpr(WideLHS, WideRHS);
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break;
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case Instruction::Sub:
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WideUse = SE->getMinusSCEV(WideLHS, WideRHS);
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break;
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}
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return WideUse == WideAR;
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};
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bool SignExtend = IsSigned;
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if (!GuessNonIVOperand(SignExtend)) {
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SignExtend = !SignExtend;
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if (!GuessNonIVOperand(SignExtend))
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return nullptr;
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}
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Value *LHS = (NarrowUse->getOperand(0) == NarrowDef)
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? WideDef
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: getExtend(NarrowUse->getOperand(0), WideType, SignExtend,
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NarrowUse);
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Value *RHS = (NarrowUse->getOperand(1) == NarrowDef)
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? WideDef
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: getExtend(NarrowUse->getOperand(1), WideType, SignExtend,
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NarrowUse);
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auto *NarrowBO = cast<BinaryOperator>(NarrowUse);
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auto *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), LHS, RHS,
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NarrowBO->getName());
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IRBuilder<> Builder(NarrowUse);
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Builder.Insert(WideBO);
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if (const auto *OBO = dyn_cast<OverflowingBinaryOperator>(NarrowBO)) {
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@ -6,7 +6,7 @@ target datalayout = "n8:16:32:64"
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target triple = "x86_64-apple-darwin"
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; CHECK-LABEL: @sloop
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; CHECK-LABEL: @loop_0
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; CHECK-LABEL: B18:
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; Only one phi now.
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; CHECK: phi
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@ -16,7 +16,7 @@ target triple = "x86_64-apple-darwin"
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; One trunc for the dummy() call.
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; CHECK-LABEL: exit24:
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; CHECK: trunc i64 {{.*}}lcssa.wide to i32
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define void @sloop(i32* %a) {
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define void @loop_0(i32* %a) {
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Prologue:
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br i1 undef, label %B18, label %B6
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@ -41,4 +41,30 @@ exit24: ; preds = %B18
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unreachable
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}
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define void @loop_1(i32 %lim) {
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; CHECK-LABEL: @loop_1(
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entry:
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%entry.cond = icmp ne i32 %lim, 0
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br i1 %entry.cond, label %loop, label %leave
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loop:
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; CHECK: loop:
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; CHECK: %indvars.iv = phi i64 [ 1, %loop.preheader ], [ %indvars.iv.next, %loop ]
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; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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; CHECK: [[IV_INC:%[^ ]+]] = add nsw i64 %indvars.iv, -1
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; CHECK: call void @dummy.i64(i64 [[IV_INC]])
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%iv = phi i32 [ 1, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add i32 %iv, 1
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%iv.inc.sub = add i32 %iv, -1
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%iv.inc.sub.zext = zext i32 %iv.inc.sub to i64
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call void @dummy.i64(i64 %iv.inc.sub.zext)
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%be.cond = icmp ult i32 %iv.inc, %lim
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br i1 %be.cond, label %loop, label %leave
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leave:
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ret void
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}
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declare void @dummy(i32)
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declare void @dummy.i64(i64)
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