[InstCombine] Opt phi(freeze(undef), C) -> phi(C, C) (#161181)
Try to choose a value for freeze that enables the PHI to be replaced with its input constants if they are equal.
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@ -5169,6 +5169,7 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
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// - or: pick -1
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// - select's condition: if the true value is constant, choose it by making
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// the condition true.
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// - phi: pick the common constant across operands
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// - default: pick 0
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//
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// Note that this transform is intentionally done here rather than
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@ -5179,9 +5180,32 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
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// TODO: This could use getBinopAbsorber() / getBinopIdentity() to avoid
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// duplicating logic for binops at least.
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auto getUndefReplacement = [&](Type *Ty) {
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Value *BestValue = nullptr;
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auto pickCommonConstantFromPHI = [](PHINode &PN) -> Value * {
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// phi(freeze(undef), C, C). Choose C for freeze so the PHI can be
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// removed.
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Constant *BestValue = nullptr;
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for (Value *V : PN.incoming_values()) {
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if (match(V, m_Freeze(m_Undef())))
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continue;
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Constant *C = dyn_cast<Constant>(V);
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if (!C)
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return nullptr;
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if (!isGuaranteedNotToBeUndefOrPoison(C))
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return nullptr;
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if (BestValue && BestValue != C)
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return nullptr;
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BestValue = C;
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}
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return BestValue;
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};
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Value *NullValue = Constant::getNullValue(Ty);
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for (const auto *U : I.users()) {
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Value *BestValue = nullptr;
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for (auto *U : I.users()) {
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Value *V = NullValue;
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if (match(U, m_Or(m_Value(), m_Value())))
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V = ConstantInt::getAllOnesValue(Ty);
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@ -5190,6 +5214,9 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
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else if (match(U, m_c_Select(m_Specific(&I), m_Value(V)))) {
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if (!isGuaranteedNotToBeUndefOrPoison(V, &AC, &I, &DT))
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V = NullValue;
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} else if (auto *PHI = dyn_cast<PHINode>(U)) {
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if (Value *MaybeV = pickCommonConstantFromPHI(*PHI))
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V = MaybeV;
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}
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if (!BestValue)
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274
llvm/test/Transforms/InstCombine/in-freeze-phi.ll
Normal file
274
llvm/test/Transforms/InstCombine/in-freeze-phi.ll
Normal file
@ -0,0 +1,274 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
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; RUN: opt -passes=instcombine -S < %s | FileCheck %s
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define i32 @phi_freeze_same_consts(i1 %c0, i1 %c1) {
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; CHECK-LABEL: define i32 @phi_freeze_same_consts(
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; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br i1 [[C0]], label %[[BB_FREEZE:.*]], label %[[BB_OTHER:.*]]
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; CHECK: [[BB_FREEZE]]:
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; CHECK-NEXT: br label %[[FINAL:.*]]
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; CHECK: [[BB_OTHER]]:
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; CHECK-NEXT: br i1 [[C1]], label %[[CA:.*]], label %[[CB:.*]]
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; CHECK: [[CA]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[CB]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[FINAL]]:
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; CHECK-NEXT: ret i32 42
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;
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entry:
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br i1 %c0, label %bb_freeze, label %bb_other
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bb_freeze:
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%f = freeze i32 undef
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br label %final
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bb_other:
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br i1 %c1, label %cA, label %cB
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cA:
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br label %final
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cB:
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br label %final
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final:
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%phi = phi i32 [ %f, %bb_freeze ], [ 42, %cA ], [ 42, %cB ]
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ret i32 %phi
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}
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define i32 @phi_freeze_mixed_consts(i1 %c0, i1 %c1) {
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; CHECK-LABEL: define i32 @phi_freeze_mixed_consts(
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; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br i1 [[C0]], label %[[BB_FREEZE:.*]], label %[[BB_OTHER:.*]]
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; CHECK: [[BB_FREEZE]]:
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; CHECK-NEXT: br label %[[FINAL:.*]]
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; CHECK: [[BB_OTHER]]:
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; CHECK-NEXT: br i1 [[C1]], label %[[CA:.*]], label %[[CB:.*]]
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; CHECK: [[CA]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[CB]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[FINAL]]:
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; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 0, %[[BB_FREEZE]] ], [ 42, %[[CA]] ], [ 7, %[[CB]] ]
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; CHECK-NEXT: ret i32 [[PHI]]
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;
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entry:
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br i1 %c0, label %bb_freeze, label %bb_other
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bb_freeze:
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%f = freeze i32 undef
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br label %final
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bb_other:
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br i1 %c1, label %cA, label %cB
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cA:
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br label %final
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cB:
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br label %final
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final:
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%phi = phi i32 [ %f, %bb_freeze ], [ 42, %cA ], [ 7, %cB ]
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ret i32 %phi
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}
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define i32 @phi_freeze_with_nonconst_incoming(i32 %x, i1 %c0, i1 %c1) {
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; CHECK-LABEL: define i32 @phi_freeze_with_nonconst_incoming(
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; CHECK-SAME: i32 [[X:%.*]], i1 [[C0:%.*]], i1 [[C1:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br i1 [[C0]], label %[[BB_FREEZE:.*]], label %[[BB_OTHER:.*]]
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; CHECK: [[BB_FREEZE]]:
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; CHECK-NEXT: br label %[[FINAL:.*]]
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; CHECK: [[BB_OTHER]]:
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; CHECK-NEXT: br i1 [[C1]], label %[[CA:.*]], label %[[CB:.*]]
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; CHECK: [[CA]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[CB]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[FINAL]]:
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; CHECK-NEXT: [[PHI:%.*]] = phi i32 [ 0, %[[BB_FREEZE]] ], [ [[X]], %[[CA]] ], [ 13, %[[CB]] ]
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; CHECK-NEXT: ret i32 [[PHI]]
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;
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entry:
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br i1 %c0, label %bb_freeze, label %bb_other
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bb_freeze:
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%f = freeze i32 undef
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br label %final
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bb_other:
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br i1 %c1, label %cA, label %cB
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cA:
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br label %final
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cB:
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br label %final
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final:
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%phi = phi i32 [ %f, %bb_freeze ], [ %x, %cA ], [ 13, %cB ]
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ret i32 %phi
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}
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define <4 x i8> @phi_freeze_vector(i1 %c0, i1 %c1) {
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; CHECK-LABEL: define <4 x i8> @phi_freeze_vector(
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; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br i1 [[C0]], label %[[BB_FREEZE:.*]], label %[[BB_OTHER:.*]]
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; CHECK: [[BB_FREEZE]]:
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; CHECK-NEXT: br label %[[FINAL:.*]]
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; CHECK: [[BB_OTHER]]:
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; CHECK-NEXT: br i1 [[C1]], label %[[CA:.*]], label %[[CB:.*]]
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; CHECK: [[CA]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[CB]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[FINAL]]:
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; CHECK-NEXT: ret <4 x i8> splat (i8 9)
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;
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entry:
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br i1 %c0, label %bb_freeze, label %bb_other
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bb_freeze:
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%f = freeze <4 x i8> undef
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br label %final
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bb_other:
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br i1 %c1, label %cA, label %cB
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cA:
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br label %final
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cB:
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br label %final
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final:
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%phi = phi <4 x i8> [ %f, %bb_freeze ],
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[<i8 9, i8 9, i8 9, i8 9>, %cA ],
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[<i8 9, i8 9, i8 9, i8 9>, %cB ]
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ret <4 x i8> %phi
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}
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define i32 @multi_use_one_folds_one_not_zero(i1 %c0, i1 %c1, i1 %c2) {
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; CHECK-LABEL: define i32 @multi_use_one_folds_one_not_zero(
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; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]], i1 [[C2:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br i1 [[C0]], label %[[BB_OTHER3:.*]], label %[[CC1:.*]]
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; CHECK: [[BB_OTHER3]]:
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; CHECK-NEXT: br label %[[MID:.*]]
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; CHECK: [[CC1]]:
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; CHECK-NEXT: br i1 [[C1]], label %[[CA:.*]], label %[[CB:.*]]
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; CHECK: [[CA]]:
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; CHECK-NEXT: br label %[[MID]]
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; CHECK: [[CB]]:
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; CHECK-NEXT: br label %[[MID]]
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; CHECK: [[MID]]:
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; CHECK-NEXT: [[PHI_FOLD:%.*]] = phi i32 [ 0, %[[BB_OTHER3]] ], [ 1, %[[CA]] ], [ 1, %[[CB]] ]
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; CHECK-NEXT: br i1 [[C2]], label %[[BB_FREEZE2:.*]], label %[[CD:.*]]
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; CHECK: [[BB_FREEZE2]]:
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; CHECK-NEXT: br label %[[FINAL:.*]]
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; CHECK: [[BB_OTHER2:.*:]]
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; CHECK-NEXT: br i1 true, label %[[CA]], label %[[CB]]
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; CHECK: [[CC:.*:]]
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[CD]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[FINAL]]:
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; CHECK-NEXT: ret i32 [[PHI_FOLD]]
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;
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entry:
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%f = freeze i32 undef
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br i1 %c0, label %bb_freeze, label %bb_other
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bb_freeze:
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br label %mid
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bb_other:
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br i1 %c1, label %cA, label %cB
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cA:
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br label %mid
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cB:
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br label %mid
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mid:
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%phi_no_fold = phi i32 [ %f, %bb_freeze ], [ 1, %cA ], [ 1, %cB ]
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br i1 %c2, label %bb_freeze2, label %cD
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bb_freeze2:
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br label %final
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bb_other2:
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br i1 %c1, label %cA, label %cB
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cC:
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br label %final
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cD:
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br label %final
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final:
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%phi_fold = phi i32 [ %f, %bb_freeze2 ], [ 0, %cC ], [ 0, %cD ]
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%a = add i32 %phi_fold, %phi_no_fold
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ret i32 %a
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}
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define i32 @phi_freeze_poison(i1 %c0, i1 %c1) {
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; CHECK-LABEL: define i32 @phi_freeze_poison(
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; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br i1 [[C0]], label %[[BB_FREEZE:.*]], label %[[BB_OTHER:.*]]
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; CHECK: [[BB_FREEZE]]:
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; CHECK-NEXT: br label %[[FINAL:.*]]
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; CHECK: [[BB_OTHER]]:
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; CHECK-NEXT: br i1 [[C1]], label %[[CA:.*]], label %[[CB:.*]]
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; CHECK: [[CA]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[CB]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[FINAL]]:
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; CHECK-NEXT: ret i32 0
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;
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entry:
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br i1 %c0, label %bb_freeze, label %bb_other
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bb_freeze:
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%f = freeze i32 undef
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br label %final
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bb_other:
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br i1 %c1, label %cA, label %cB
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cA:
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br label %final
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cB:
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br label %final
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final:
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%phi = phi i32 [ %f, %bb_freeze ], [ poison, %cA ], [ poison, %cB ]
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ret i32 %phi
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}
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define <2 x i32> @phi_freeze_poison_vec(i1 %c0, i1 %c1) {
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; CHECK-LABEL: define <2 x i32> @phi_freeze_poison_vec(
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; CHECK-SAME: i1 [[C0:%.*]], i1 [[C1:%.*]]) {
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; CHECK-NEXT: [[ENTRY:.*:]]
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; CHECK-NEXT: br i1 [[C0]], label %[[BB_FREEZE:.*]], label %[[BB_OTHER:.*]]
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; CHECK: [[BB_FREEZE]]:
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; CHECK-NEXT: br label %[[FINAL:.*]]
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; CHECK: [[BB_OTHER]]:
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; CHECK-NEXT: br i1 [[C1]], label %[[CA:.*]], label %[[CB:.*]]
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; CHECK: [[CA]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[CB]]:
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; CHECK-NEXT: br label %[[FINAL]]
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; CHECK: [[FINAL]]:
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; CHECK-NEXT: [[PHI:%.*]] = phi <2 x i32> [ zeroinitializer, %[[BB_FREEZE]] ], [ <i32 poison, i32 1>, %[[CA]] ], [ <i32 poison, i32 1>, %[[CB]] ]
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; CHECK-NEXT: ret <2 x i32> [[PHI]]
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;
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entry:
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br i1 %c0, label %bb_freeze, label %bb_other
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bb_freeze:
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%f = freeze <2 x i32> undef
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br label %final
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bb_other:
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br i1 %c1, label %cA, label %cB
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cA:
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br label %final
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cB:
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br label %final
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final:
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%phi = phi <2 x i32> [ %f, %bb_freeze ], [ <i32 poison, i32 1>, %cA ], [ <i32 poison, i32 1>, %cB ]
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ret <2 x i32> %phi
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}
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