[SCCP] Remove forcedconstant, go to overdefined instead (aadb635e) · Commits · llvm-doe / llvm-project

llvm/lib/Transforms/Scalar/SCCP.cpp

+16 −232

Original line number	Diff line number	Diff line
		@@ -85,19 +85,13 @@ class LatticeVal {
		/// constant - This LLVM Value has a specific constant value.
		constant,

		/// forcedconstant - This LLVM Value was thought to be undef until
		/// ResolvedUndefsIn. This is treated just like 'constant', but if merged
		/// with another (different) constant, it goes to overdefined, instead of
		/// asserting.
		forcedconstant,

		/// overdefined - This instruction is not known to be constant, and we know
		/// it has a value.
		overdefined
		};

		/// Val: This stores the current lattice value along with the Constant* for
		/// the constant if this is a 'constant' or 'forcedconstant' value.
		/// the constant if this is a 'constant' value.
		PointerIntPair<Constant *, 2, LatticeValueTy> Val;

		LatticeValueTy getLatticeValue() const {
		@@ -109,9 +103,7 @@ public:

		bool isUnknown() const { return getLatticeValue() == unknown; }

		bool isConstant() const {
		return getLatticeValue() == constant \|\| getLatticeValue() == forcedconstant;
		}
		bool isConstant() const { return getLatticeValue() == constant; }

		bool isOverdefined() const { return getLatticeValue() == overdefined; }

		@@ -131,26 +123,15 @@ public:

		/// markConstant - Return true if this is a change in status.
		bool markConstant(Constant *V) {
		if (getLatticeValue() == constant) { // Constant but not forcedconstant.
		if (getLatticeValue() == constant) { // Constant
		assert(getConstant() == V && "Marking constant with different value");
		return false;
		}

		if (isUnknown()) {
		assert(isUnknown());
		Val.setInt(constant);
		assert(V && "Marking constant with NULL");
		Val.setPointer(V);
		} else {
		assert(getLatticeValue() == forcedconstant &&
		"Cannot move from overdefined to constant!");
		// Stay at forcedconstant if the constant is the same.
		if (V == getConstant()) return false;

		// Otherwise, we go to overdefined. Assumptions made based on the
		// forced value are possibly wrong. Assuming this is another constant
		// could expose a contradiction.
		Val.setInt(overdefined);
		}
		return true;
		}

		@@ -170,12 +151,6 @@ public:
		return nullptr;
		}

		void markForcedConstant(Constant *V) {
		assert(isUnknown() && "Can't force a defined value!");
		Val.setInt(forcedconstant);
		Val.setPointer(V);
		}

		ValueLatticeElement toValueLattice() const {
		if (isOverdefined())
		return ValueLatticeElement::getOverdefined();
		@@ -421,7 +396,7 @@ public:
		}

		private:
		// pushToWorkList - Helper for markConstant/markForcedConstant/markOverdefined
		// pushToWorkList - Helper for markConstant/markOverdefined
		void pushToWorkList(LatticeVal &IV, Value *V) {
		if (IV.isOverdefined())
		return OverdefinedInstWorkList.push_back(V);
		@@ -443,14 +418,6 @@ private:
		return markConstant(ValueState[V], V, C);
		}

		void markForcedConstant(Value V, Constant C) {
		assert(!V->getType()->isStructTy() && "structs should use mergeInValue");
		LatticeVal &IV = ValueState[V];
		IV.markForcedConstant(C);
		LLVM_DEBUG(dbgs() << "markForcedConstant: " << C << ": " << V << '\n');
		pushToWorkList(IV, V);
		}

		// markOverdefined - Make a value be marked as "overdefined". If the
		// value is not already overdefined, add it to the overdefined instruction
		// work list so that the users of the instruction are updated later.
		@@ -1032,8 +999,10 @@ void SCCPSolver::visitBinaryOperator(Instruction &I) {
		}

		// If something is undef, wait for it to resolve.
		if (!V1State.isOverdefined() && !V2State.isOverdefined())
		if (!V1State.isOverdefined() && !V2State.isOverdefined()) {

		return;
		}

		// Otherwise, one of our operands is overdefined. Try to produce something
		// better than overdefined with some tricks.
		@@ -1449,10 +1418,8 @@ void SCCPSolver::Solve() {
		/// constraints on the condition of the branch, as that would impact other users
		/// of the value.
		///
		/// This scan also checks for values that use undefs, whose results are actually
		/// defined. For example, 'zext i8 undef to i32' should produce all zeros
		/// conservatively, as "(zext i8 X -> i32) & 0xFF00" must always return zero,
		/// even if X isn't defined.
		/// This scan also checks for values that use undefs. It conservatively marks
		/// them as overdefined.
		bool SCCPSolver::ResolvedUndefsIn(Function &F) {
		for (BasicBlock &BB : F) {
		if (!BBExecutable.count(&BB))
		@@ -1475,7 +1442,6 @@ bool SCCPSolver::ResolvedUndefsIn(Function &F) {
		// tracked as precisely as their operands.
		if (isa<ExtractValueInst>(I) \|\| isa<InsertValueInst>(I))
		continue;

		// Send the results of everything else to overdefined. We could be
		// more precise than this but it isn't worth bothering.
		for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
		@@ -1495,195 +1461,13 @@ bool SCCPSolver::ResolvedUndefsIn(Function &F) {
		// 2. It could be constant-foldable.
		// Because of the way we solve return values, tracked calls must
		// never be marked overdefined in ResolvedUndefsIn.
		if (CallSite CS = CallSite(&I)) {
		if (CallSite CS = CallSite(&I))
		if (Function *F = CS.getCalledFunction())
		if (TrackedRetVals.count(F))
		continue;

		// If the call is constant-foldable, we mark it overdefined because
		// we do not know what return values are valid.
		markOverdefined(&I);
		return true;
		}

		// extractvalue is safe; check here because the argument is a struct.
		if (isa<ExtractValueInst>(I))
		continue;

		// Compute the operand LatticeVals, for convenience below.
		// Anything taking a struct is conservatively assumed to require
		// overdefined markings.
		if (I.getOperand(0)->getType()->isStructTy()) {
		markOverdefined(&I);
		return true;
		}
		LatticeVal Op0LV = getValueState(I.getOperand(0));
		LatticeVal Op1LV;
		if (I.getNumOperands() == 2) {
		if (I.getOperand(1)->getType()->isStructTy()) {
		markOverdefined(&I);
		return true;
		}

		Op1LV = getValueState(I.getOperand(1));
		}
		// If this is an instructions whose result is defined even if the input is
		// not fully defined, propagate the information.
		Type *ITy = I.getType();
		switch (I.getOpcode()) {
		case Instruction::Add:
		case Instruction::Sub:
		case Instruction::Trunc:
		case Instruction::FPTrunc:
		case Instruction::BitCast:
		break; // Any undef -> undef
		case Instruction::FSub:
		case Instruction::FAdd:
		case Instruction::FMul:
		case Instruction::FDiv:
		case Instruction::FRem:
		// Floating-point binary operation: be conservative.
		if (Op0LV.isUnknown() && Op1LV.isUnknown())
		markForcedConstant(&I, Constant::getNullValue(ITy));
		else
		markOverdefined(&I);
		return true;
		case Instruction::FNeg:
		break; // fneg undef -> undef
		case Instruction::ZExt:
		case Instruction::SExt:
		case Instruction::FPToUI:
		case Instruction::FPToSI:
		case Instruction::FPExt:
		case Instruction::PtrToInt:
		case Instruction::IntToPtr:
		case Instruction::SIToFP:
		case Instruction::UIToFP:
		// undef -> 0; some outputs are impossible
		markForcedConstant(&I, Constant::getNullValue(ITy));
		return true;
		case Instruction::Mul:
		case Instruction::And:
		// Both operands undef -> undef
		if (Op0LV.isUnknown() && Op1LV.isUnknown())
		break;
		// undef * X -> 0. X could be zero.
		// undef & X -> 0. X could be zero.
		markForcedConstant(&I, Constant::getNullValue(ITy));
		return true;
		case Instruction::Or:
		// Both operands undef -> undef
		if (Op0LV.isUnknown() && Op1LV.isUnknown())
		break;
		// undef \| X -> -1. X could be -1.
		markForcedConstant(&I, Constant::getAllOnesValue(ITy));
		return true;
		case Instruction::Xor:
		// undef ^ undef -> 0; strictly speaking, this is not strictly
		// necessary, but we try to be nice to people who expect this
		// behavior in simple cases
		if (Op0LV.isUnknown() && Op1LV.isUnknown()) {
		markForcedConstant(&I, Constant::getNullValue(ITy));
		return true;
		}
		// undef ^ X -> undef
		break;
		case Instruction::SDiv:
		case Instruction::UDiv:
		case Instruction::SRem:
		case Instruction::URem:
		// X / undef -> undef. No change.
		// X % undef -> undef. No change.
		if (Op1LV.isUnknown()) break;

		// X / 0 -> undef. No change.
		// X % 0 -> undef. No change.
		if (Op1LV.isConstant() && Op1LV.getConstant()->isZeroValue())
		break;

		// undef / X -> 0. X could be maxint.
		// undef % X -> 0. X could be 1.
		markForcedConstant(&I, Constant::getNullValue(ITy));
		return true;
		case Instruction::AShr:
		// X >>a undef -> undef.
		if (Op1LV.isUnknown()) break;

		// Shifting by the bitwidth or more is undefined.
		if (Op1LV.isConstant()) {
		if (auto *ShiftAmt = Op1LV.getConstantInt())
		if (ShiftAmt->getLimitedValue() >=
		ShiftAmt->getType()->getScalarSizeInBits())
		break;
		}

		// undef >>a X -> 0
		markForcedConstant(&I, Constant::getNullValue(ITy));
		return true;
		case Instruction::LShr:
		case Instruction::Shl:
		// X << undef -> undef.
		// X >> undef -> undef.
		if (Op1LV.isUnknown()) break;

		// Shifting by the bitwidth or more is undefined.
		if (Op1LV.isConstant()) {
		if (auto *ShiftAmt = Op1LV.getConstantInt())
		if (ShiftAmt->getLimitedValue() >=
		ShiftAmt->getType()->getScalarSizeInBits())
		break;
		}

		// undef << X -> 0
		// undef >> X -> 0
		markForcedConstant(&I, Constant::getNullValue(ITy));
		return true;
		case Instruction::Select:
		Op1LV = getValueState(I.getOperand(1));
		// undef ? X : Y -> X or Y. There could be commonality between X/Y.
		if (Op0LV.isUnknown()) {
		if (!Op1LV.isConstant()) // Pick the constant one if there is any.
		Op1LV = getValueState(I.getOperand(2));
		} else if (Op1LV.isUnknown()) {
		// c ? undef : undef -> undef. No change.
		Op1LV = getValueState(I.getOperand(2));
		if (Op1LV.isUnknown())
		break;
		// Otherwise, c ? undef : x -> x.
		} else {
		// Leave Op1LV as Operand(1)'s LatticeValue.
		}

		if (Op1LV.isConstant())
		markForcedConstant(&I, Op1LV.getConstant());
		else
		markOverdefined(&I);
		return true;
		case Instruction::Load:
		// A load here means one of two things: a load of undef from a global,
		// a load from an unknown pointer. Either way, having it return undef
		// is okay.
		break;
		case Instruction::ICmp:
		// X == undef -> undef. Other comparisons get more complicated.
		Op0LV = getValueState(I.getOperand(0));
		Op1LV = getValueState(I.getOperand(1));

		if ((Op0LV.isUnknown() \|\| Op1LV.isUnknown()) &&
		cast<ICmpInst>(&I)->isEquality())
		break;
		markOverdefined(&I);
		return true;
		case Instruction::Call:
		case Instruction::Invoke:
		case Instruction::CallBr:
		llvm_unreachable("Call-like instructions should have be handled early");
		default:
		// If we don't know what should happen here, conservatively mark it
		// overdefined.
		markOverdefined(&I);
		return true;
		}
		}

		// Check to see if we have a branch or switch on an undefined value. If so

llvm/test/Transforms/IPConstantProp/PR16052.ll

+6 −3

Original line number	Diff line number	Diff line
		@@ -7,7 +7,9 @@ target triple = "x86_64-unknown-linux-gnu"
		define i64 @fn2() {
		; CHECK-LABEL: define {{[^@]+}}@fn2()
		; CHECK-NEXT: entry:
		; CHECK-NEXT: [[CALL2:%.*]] = call i64 @fn1(i64 undef)
		; CHECK-NEXT: [[CONV:%.*]] = sext i32 undef to i64
		; CHECK-NEXT: [[DIV:%.*]] = sdiv i64 8, [[CONV]]
		; CHECK-NEXT: [[CALL2:%.*]] = call i64 @fn1(i64 [[DIV]])
		; CHECK-NEXT: ret i64 [[CALL2]]
		;
		entry:
		@@ -21,7 +23,8 @@ define internal i64 @fn1(i64 %p1) {
		; CHECK-LABEL: define {{[^@]+}}@fn1
		; CHECK-SAME: (i64 [[P1:%.*]])
		; CHECK-NEXT: entry:
		; CHECK-NEXT: [[COND:%.*]] = select i1 undef, i64 undef, i64 undef
		; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne i64 [[P1]], 0
		; CHECK-NEXT: [[COND:%.*]] = select i1 [[TOBOOL]], i64 [[P1]], i64 [[P1]]
		; CHECK-NEXT: ret i64 [[COND]]
		;
		entry:

llvm/test/Transforms/IPConstantProp/PR26044.ll

+4 −2

Original line number	Diff line number	Diff line
		@@ -11,7 +11,8 @@ define void @fn2(i32* %P) {
		; CHECK: for.cond1:
		; CHECK-NEXT: br i1 false, label [[IF_END]], label [[IF_END]]
		; CHECK: if.end:
		; CHECK-NEXT: [[CALL:%.*]] = call i32 @fn1(i32 undef)
		; CHECK-NEXT: [[TMP0:%.]] = load i32, i32 null, align 4
		; CHECK-NEXT: [[CALL:%.*]] = call i32 @fn1(i32 [[TMP0]])
		; CHECK-NEXT: store i32 [[CALL]], i32* [[P]]
		; CHECK-NEXT: br label [[FOR_COND1:%.*]]
		;
		@@ -33,7 +34,8 @@ define internal i32 @fn1(i32 %p1) {
		; CHECK-LABEL: define {{[^@]+}}@fn1
		; CHECK-SAME: (i32 [[P1:%.*]])
		; CHECK-NEXT: entry:
		; CHECK-NEXT: [[COND:%.*]] = select i1 undef, i32 undef, i32 undef
		; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ne i32 [[P1]], 0
		; CHECK-NEXT: [[COND:%.*]] = select i1 [[TOBOOL]], i32 [[P1]], i32 [[P1]]
		; CHECK-NEXT: ret i32 [[COND]]
		;
		entry:

llvm/test/Transforms/SCCP/2006-12-19-UndefBug.ll

+8 −4

Original line number	Diff line number	Diff line
		; RUN: opt < %s -sccp -S \| \
		; RUN: grep "ret i1 false"
		; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
		; RUN: opt < %s -sccp -S \| FileCheck %s

		define i1 @foo() {
		; CHECK-LABEL: @foo(
		; CHECK-NEXT: [[X:%.*]] = and i1 false, undef
		; CHECK-NEXT: ret i1 [[X]]
		;
		%X = and i1 false, undef ; <i1> [#uses=1]
		ret i1 %X
		}

llvm/test/Transforms/SCCP/apint-bigint2.ll

+23 −1

Original line number	Diff line number	Diff line
		@@ -18,7 +18,13 @@ define i101 @array() {
		}

		; CHECK-LABEL: @large_aggregate
		; CHECK-NEXT: ret i101 undef
		; CHECK-NEXT: %B = load i101, i101* undef
		; CHECK-NEXT: %D = and i101 %B, 1
		; CHECK-NEXT: %DD = or i101 %D, 1
		; CHECK-NEXT: %G = getelementptr i101, i101* getelementptr inbounds ([6 x i101], [6 x i101]* @Y, i32 0, i32 5), i101 %DD
		; CHECK-NEXT: %L3 = load i101, i101* %G
		; CHECK-NEXT: ret i101 %L3
		;
		define i101 @large_aggregate() {
		%B = load i101, i101* undef
		%D = and i101 %B, 1
		@@ -29,6 +35,22 @@ define i101 @large_aggregate() {
		ret i101 %L3
		}

		; CHECK-LABEL: define i101 @large_aggregate_2() {
		; CHECK-NEXT: %D = and i101 undef, 1
		; CHECK-NEXT: %DD = or i101 %D, 1
		; CHECK-NEXT: %G = getelementptr i101, i101* getelementptr inbounds ([6 x i101], [6 x i101]* @Y, i32 0, i32 5), i101 %DD
		; CHECK-NEXT: %L3 = load i101, i101* %G
		; CHECK-NEXT: ret i101 %L3
		;
		define i101 @large_aggregate_2() {
		%D = and i101 undef, 1
		%DD = or i101 %D, 1
		%F = getelementptr [6 x i101], [6 x i101]* @Y, i32 0, i32 5
		%G = getelementptr i101, i101* %F, i101 %DD
		%L3 = load i101, i101* %G
		ret i101 %L3
		}

		; CHECK-LABEL: @index_too_large
		; CHECK-NEXT: store i101* getelementptr (i101, i101* getelementptr ([6 x i101], [6 x i101]* @Y, i32 0, i32 -1), i101 9224497936761618431), i101** undef
		; CHECK-NEXT: ret void

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