[SCEV] Disallow simplifying phi(undef, X) to X (#115109)

See the following case: ``` @GlobIntONE = global i32 0, align 4 define ptr @src() { entry: br label %for.body.peel.begin for.body.peel.begin: ; preds = %entry br label %for.body.peel for.body.peel: ; preds = %for.body.peel.begin br i1 true, label %cleanup.peel, label %cleanup.loopexit.peel cleanup.loopexit.peel: ; preds = %for.body.peel br label %cleanup.peel cleanup.peel: ; preds = %cleanup.loopexit.peel, %for.body.peel %retval.2.peel = phi ptr [ undef, %for.body.peel ], [ @GlobIntONE, %cleanup.loopexit.peel ] br i1 true, label %for.body.peel.next, label %cleanup7 for.body.peel.next: ; preds = %cleanup.peel br label %for.body.peel.next1 for.body.peel.next1: ; preds = %for.body.peel.next br label %entry.peel.newph entry.peel.newph: ; preds = %for.body.peel.next1 br label %for.body for.body: ; preds = %cleanup, %entry.peel.newph %retval.0 = phi ptr [ %retval.2.peel, %entry.peel.newph ], [ %retval.2, %cleanup ] br i1 false, label %cleanup, label %cleanup.loopexit cleanup.loopexit: ; preds = %for.body br label %cleanup cleanup: ; preds = %cleanup.loopexit, %for.body %retval.2 = phi ptr [ %retval.0, %for.body ], [ @GlobIntONE, %cleanup.loopexit ] br i1 false, label %for.body, label %cleanup7.loopexit cleanup7.loopexit: ; preds = %cleanup %retval.2.lcssa.ph = phi ptr [ %retval.2, %cleanup ] br label %cleanup7 cleanup7: ; preds = %cleanup7.loopexit, %cleanup.peel %retval.2.lcssa = phi ptr [ %retval.2.peel, %cleanup.peel ], [ %retval.2.lcssa.ph, %cleanup7.loopexit ] ret ptr %retval.2.lcssa } define ptr @tgt() { entry: br label %for.body.peel.begin for.body.peel.begin: ; preds = %entry br label %for.body.peel for.body.peel: ; preds = %for.body.peel.begin br i1 true, label %cleanup.peel, label %cleanup.loopexit.peel cleanup.loopexit.peel: ; preds = %for.body.peel br label %cleanup.peel cleanup.peel: ; preds = %cleanup.loopexit.peel, %for.body.peel %retval.2.peel = phi ptr [ undef, %for.body.peel ], [ @GlobIntONE, %cleanup.loopexit.peel ] br i1 true, label %for.body.peel.next, label %cleanup7 for.body.peel.next: ; preds = %cleanup.peel br label %for.body.peel.next1 for.body.peel.next1: ; preds = %for.body.peel.next br label %entry.peel.newph entry.peel.newph: ; preds = %for.body.peel.next1 br label %for.body for.body: ; preds = %cleanup, %entry.peel.newph br i1 false, label %cleanup, label %cleanup.loopexit cleanup.loopexit: ; preds = %for.body br label %cleanup cleanup: ; preds = %cleanup.loopexit, %for.body br i1 false, label %for.body, label %cleanup7.loopexit cleanup7.loopexit: ; preds = %cleanup %retval.2.lcssa.ph = phi ptr [ %retval.2.peel, %cleanup ] br label %cleanup7 cleanup7: ; preds = %cleanup7.loopexit, %cleanup.peel %retval.2.lcssa = phi ptr [ %retval.2.peel, %cleanup.peel ], [ %retval.2.lcssa.ph, %cleanup7.loopexit ] ret ptr %retval.2.lcssa } ``` 1. `simplifyInstruction(%retval.2.peel)` returns `@GlobIntONE`. Thus, `ScalarEvolution::createNodeForPHI` returns SCEV expr `@GlobIntONE` for `%retval.2.peel`. 2. `SimplifyIndvar::replaceIVUserWithLoopInvariant` tries to replace the use of `%retval.2.peel` in `%retval.2.lcssa.ph` with `@GlobIntONE`. 3. `simplifyLoopAfterUnroll -> simplifyLoopIVs -> SCEVExpander::expand` reuses `%retval.2.peel = phi ptr [ undef, %for.body.peel ], [ @GlobIntONE, %cleanup.loopexit.peel ]` to generate code for `@GlobIntONE`. It is incorrect. This patch disallows simplifying `phi(undef, X)` to `X` by setting `CanUseUndef` to false. Closes #114879.
llvm · Nov 7, 2024 · 0b9f1cc · 0b9f1cc
1 parent 3850801
commit 0b9f1cc
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diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6023,7 +6023,11 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
   if (const SCEV *S = createAddRecFromPHI(PN))
     return S;
 
-  if (Value *V = simplifyInstruction(PN, {getDataLayout(), &TLI, &DT, &AC}))
+  // We do not allow simplifying phi (undef, X) to X here, to avoid reusing the
+  // phi node for X.
+  if (Value *V = simplifyInstruction(
+          PN, {getDataLayout(), &TLI, &DT, &AC, /*CtxI=*/nullptr,
+               /*UseInstrInfo=*/true, /*CanUseUndef=*/false}))
     return getSCEV(V);
 
   if (const SCEV *S = createNodeFromSelectLikePHI(PN))

diff --git a/llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll b/llvm/test/Transforms/IndVarSimplify/invalidate-modified-lcssa-phi.ll
@@ -48,13 +48,14 @@ define i8 @test_pr52023(i1 %c.1, i1 %c.2) {
 ; CHECK-NEXT:    br label [[LOOP_1:%.*]]
 ; CHECK:       loop.1:
 ; CHECK-NEXT:    [[INC79:%.*]] = phi i8 [ [[TMP0:%.*]], [[LOOP_1_LATCH:%.*]] ], [ 0, [[ENTRY:%.*]] ]
-; CHECK-NEXT:    [[TMP0]] = add i8 [[INC79]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[INC79]], 1
 ; CHECK-NEXT:    br label [[LOOP_2:%.*]]
 ; CHECK:       loop.2:
 ; CHECK-NEXT:    br i1 [[C_1:%.*]], label [[LOOP_2_LATCH:%.*]], label [[LOOP_1_LATCH]]
 ; CHECK:       loop.2.latch:
 ; CHECK-NEXT:    br label [[LOOP_1_LATCH]]
 ; CHECK:       loop.1.latch:
+; CHECK-NEXT:    [[TMP0]] = phi i8 [ [[TMP1]], [[LOOP_2_LATCH]] ], [ undef, [[LOOP_2]] ]
 ; CHECK-NEXT:    br i1 [[C_2:%.*]], label [[EXIT:%.*]], label [[LOOP_1]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[INC_LCSSA_LCSSA:%.*]] = phi i8 [ [[TMP0]], [[LOOP_1_LATCH]] ]

diff --git a/llvm/test/Transforms/IndVarSimplify/no-iv-rewrite.ll b/llvm/test/Transforms/IndVarSimplify/no-iv-rewrite.ll
@@ -260,11 +260,13 @@ define void @identityphi(i32 %limit) nounwind {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    br i1 undef, label [[IF_THEN:%.*]], label [[CONTROL:%.*]]
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[CONTROL:%.*]] ]
+; CHECK-NEXT:    br i1 undef, label [[IF_THEN:%.*]], label [[CONTROL]]
 ; CHECK:       if.then:
 ; CHECK-NEXT:    br label [[CONTROL]]
 ; CHECK:       control:
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 0, [[LIMIT:%.*]]
+; CHECK-NEXT:    [[IV_NEXT]] = phi i32 [ [[IV]], [[LOOP]] ], [ undef, [[IF_THEN]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[IV_NEXT]], [[LIMIT:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void

diff --git a/llvm/test/Transforms/LoopStrengthReduce/X86/2012-01-13-phielim.ll b/llvm/test/Transforms/LoopStrengthReduce/X86/2012-01-13-phielim.ll
@@ -156,29 +156,29 @@ define fastcc void @test3(ptr nocapture %u) nounwind uwtable ssp {
 ; CHECK:       for.inc8.us.i:
 ; CHECK-NEXT:    br i1 true, label [[MESHBB1_LOOPEXIT:%.*]], label [[MESHBB:%.*]]
 ; CHECK:       for.body3.us.i:
-; CHECK-NEXT:    [[INDVARS_IV_I_SV_PHI:%.*]] = phi i64 [ [[INDVARS_IV_NEXT_I:%.*]], [[MESHBB]] ], [ 0, [[FOR_BODY3_LR_PH_US_I:%.*]] ]
+; CHECK-NEXT:    [[TMP:%.*]] = phi i32 [ [[LSR_IV_NEXT:%.*]], [[MESHBB]] ], [ [[TMP3:%.*]], [[FOR_BODY3_LR_PH_US_I:%.*]] ]
+; CHECK-NEXT:    [[SCEVGEP:%.*]] = phi ptr [ [[SCEVGEP1:%.*]], [[MESHBB]] ], [ [[U:%.*]], [[FOR_BODY3_LR_PH_US_I]] ]
 ; CHECK-NEXT:    [[OPQ_SA_CALC12:%.*]] = sub i32 undef, 227
-; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[LSR_IV:%.*]], [[INDVARS_IV_I_SV_PHI]]
-; CHECK-NEXT:    [[TMP:%.*]] = trunc i64 [[TMP0]] to i32
 ; CHECK-NEXT:    [[MUL_I_US_I:%.*]] = mul nsw i32 0, [[TMP]]
-; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw nsw i64 [[INDVARS_IV_I_SV_PHI]], 3
-; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, ptr [[U:%.*]], i64 [[TMP1]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = load double, ptr [[SCEVGEP]], align 8
 ; CHECK-NEXT:    br i1 undef, label [[FOR_INC8_US_I:%.*]], label [[MESHBB]]
 ; CHECK:       for.body3.lr.ph.us.i.loopexit:
-; CHECK-NEXT:    [[LSR_IV_NEXT:%.*]] = add i64 [[LSR_IV]], 1
 ; CHECK-NEXT:    br label [[FOR_BODY3_LR_PH_US_I]]
 ; CHECK:       for.body3.lr.ph.us.i:
-; CHECK-NEXT:    [[LSR_IV]] = phi i64 [ [[LSR_IV_NEXT]], [[FOR_BODY3_LR_PH_US_I_LOOPEXIT:%.*]] ], [ undef, [[MESHBB1]] ]
+; CHECK-NEXT:    [[LSR_IV:%.*]] = phi i64 [ undef, [[MESHBB1]] ], [ [[INDVARS_IV8_I_SV_PHI24:%.*]], [[FOR_BODY3_LR_PH_US_I_LOOPEXIT:%.*]] ]
 ; CHECK-NEXT:    [[ARRAYIDX_US_I:%.*]] = getelementptr inbounds double, ptr undef, i64 [[LSR_IV]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[LSR_IV]], 1
+; CHECK-NEXT:    [[TMP3]] = trunc i64 [[LSR_IV]] to i32
 ; CHECK-NEXT:    br label [[FOR_BODY3_US_I:%.*]]
 ; CHECK:       for.inc8.us.i2:
 ; CHECK-NEXT:    unreachable
 ; CHECK:       eval_At_times_u.exit:
 ; CHECK-NEXT:    ret void
 ; CHECK:       meshBB:
+; CHECK-NEXT:    [[INDVARS_IV8_I_SV_PHI24]] = phi i64 [ undef, [[FOR_BODY3_US_I]] ], [ [[TMP1]], [[FOR_INC8_US_I]] ]
 ; CHECK-NEXT:    [[MESHSTACKVARIABLE_PHI:%.*]] = phi i32 [ [[OPQ_SA_CALC12]], [[FOR_BODY3_US_I]] ], [ undef, [[FOR_INC8_US_I]] ]
-; CHECK-NEXT:    [[INDVARS_IV_NEXT_I]] = add i64 [[INDVARS_IV_I_SV_PHI]], 1
+; CHECK-NEXT:    [[SCEVGEP1]] = getelementptr i8, ptr [[SCEVGEP]], i64 8
+; CHECK-NEXT:    [[LSR_IV_NEXT]] = add i32 [[TMP]], 1
 ; CHECK-NEXT:    br i1 true, label [[FOR_BODY3_LR_PH_US_I_LOOPEXIT]], label [[FOR_BODY3_US_I]]
 ; CHECK:       meshBB1.loopexit:
 ; CHECK-NEXT:    br label [[MESHBB1]]

diff --git a/llvm/test/Transforms/LoopUnroll/pr114879.ll b/llvm/test/Transforms/LoopUnroll/pr114879.ll
@@ -0,0 +1,62 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=loop-unroll-full -unroll-full-max-count=1 %s | FileCheck %s
+
+@GlobIntONE = global i32 0, align 4
+
+; Make sure we don't reuse the phi (undef, X) for X.
+
+define ptr @test() {
+; CHECK-LABEL: define ptr @test() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br label %[[FOR_BODY_PEEL_BEGIN:.*]]
+; CHECK:       [[FOR_BODY_PEEL_BEGIN]]:
+; CHECK-NEXT:    br label %[[FOR_BODY_PEEL:.*]]
+; CHECK:       [[FOR_BODY_PEEL]]:
+; CHECK-NEXT:    br i1 true, label %[[CLEANUP_PEEL:.*]], label %[[CLEANUP_LOOPEXIT_PEEL:.*]]
+; CHECK:       [[CLEANUP_LOOPEXIT_PEEL]]:
+; CHECK-NEXT:    br label %[[CLEANUP_PEEL]]
+; CHECK:       [[CLEANUP_PEEL]]:
+; CHECK-NEXT:    [[RETVAL_2_PEEL:%.*]] = phi ptr [ undef, %[[FOR_BODY_PEEL]] ], [ @GlobIntONE, %[[CLEANUP_LOOPEXIT_PEEL]] ]
+; CHECK-NEXT:    br i1 true, label %[[FOR_BODY_PEEL_NEXT:.*]], label %[[CLEANUP2:.*]]
+; CHECK:       [[FOR_BODY_PEEL_NEXT]]:
+; CHECK-NEXT:    br label %[[FOR_BODY_PEEL_NEXT1:.*]]
+; CHECK:       [[FOR_BODY_PEEL_NEXT1]]:
+; CHECK-NEXT:    br label %[[ENTRY_PEEL_NEWPH:.*]]
+; CHECK:       [[ENTRY_PEEL_NEWPH]]:
+; CHECK-NEXT:    br label %[[FOR_BODY:.*]]
+; CHECK:       [[FOR_BODY]]:
+; CHECK-NEXT:    br i1 false, label %[[CLEANUP:.*]], label %[[CLEANUP_LOOPEXIT:.*]]
+; CHECK:       [[CLEANUP_LOOPEXIT]]:
+; CHECK-NEXT:    br label %[[CLEANUP]]
+; CHECK:       [[CLEANUP]]:
+; CHECK-NEXT:    br i1 false, label %[[FOR_BODY]], label %[[CLEANUP2_LOOPEXIT:.*]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       [[CLEANUP2_LOOPEXIT]]:
+; CHECK-NEXT:    [[RETVAL_2_LCSSA_PH:%.*]] = phi ptr [ @GlobIntONE, %[[CLEANUP]] ]
+; CHECK-NEXT:    br label %[[CLEANUP2]]
+; CHECK:       [[CLEANUP2]]:
+; CHECK-NEXT:    [[RETVAL_2_LCSSA:%.*]] = phi ptr [ [[RETVAL_2_PEEL]], %[[CLEANUP_PEEL]] ], [ [[RETVAL_2_LCSSA_PH]], %[[CLEANUP2_LOOPEXIT]] ]
+; CHECK-NEXT:    ret ptr [[RETVAL_2_LCSSA]]
+;
+entry:
+  br label %for.body
+
+for.body:
+  %retval.0 = phi ptr [ undef, %entry ], [ %retval.2, %cleanup ]
+  %cmp1.not = phi i1 [ true, %entry ], [ false, %cleanup ]
+  br i1 %cmp1.not, label %cleanup, label %cleanup.loopexit
+
+cleanup.loopexit:
+  br label %cleanup
+
+cleanup:
+  %retval.2 = phi ptr [ %retval.0, %for.body ], [ @GlobIntONE, %cleanup.loopexit ]
+  br i1 %cmp1.not, label %for.body, label %cleanup2
+
+cleanup2:
+  %retval.2.lcssa = phi ptr [ %retval.2, %cleanup ]
+  ret ptr %retval.2.lcssa
+}
+;.
+; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]]}
+; CHECK: [[META1]] = !{!"llvm.loop.peeled.count", i32 1}
+;.
diff --git a/llvm/test/Transforms/LoopVectorize/uniform-blend.ll b/llvm/test/Transforms/LoopVectorize/uniform-blend.ll
@@ -14,9 +14,9 @@ define void @blend_uniform_iv_trunc(i1 %c) {
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = trunc i64 [[INDEX]] to i16
 ; CHECK-NEXT:    [[TMP1:%.*]] = add i16 [[TMP0]], 0
-; CHECK-NEXT:    [[PREDPHI:%.*]] = select i1 [[C]], i16 [[TMP1]], i16 undef
-; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i16 [[PREDPHI]]
-; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds i16, ptr [[TMP2]], i32 0
+; CHECK-NEXT:    [[TMP6:%.*]] = select i1 [[C]], i16 [[TMP1]], i16 poison
+; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i16 [[TMP6]]
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr inbounds i16, ptr [[TMP7]], i32 0
 ; CHECK-NEXT:    store <4 x i16> zeroinitializer, ptr [[TMP3]], align 2
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[TMP4:%.*]] = icmp eq i64 [[INDEX_NEXT]], 32
@@ -33,7 +33,7 @@ define void @blend_uniform_iv_trunc(i1 %c) {
 ; CHECK:       [[LOOP_NEXT]]:
 ; CHECK-NEXT:    br label %[[LOOP_LATCH]]
 ; CHECK:       [[LOOP_LATCH]]:
-; CHECK-NEXT:    [[BLEND:%.*]] = phi i16 [ undef, %[[LOOP_HEADER]] ], [ [[IV_TRUNC_2]], %[[LOOP_NEXT]] ]
+; CHECK-NEXT:    [[BLEND:%.*]] = phi i16 [ poison, %[[LOOP_HEADER]] ], [ [[IV_TRUNC_2]], %[[LOOP_NEXT]] ]
 ; CHECK-NEXT:    [[DST_PTR:%.*]] = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i16 [[BLEND]]
 ; CHECK-NEXT:    store i16 0, ptr [[DST_PTR]], align 2
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
@@ -54,7 +54,7 @@ loop.next:                                        ; preds = %loop.header
   br label %loop.latch
 
 loop.latch:                                       ; preds = %loop.next, %loop.header
-  %blend = phi i16 [ undef, %loop.header ], [ %iv.trunc.2, %loop.next ]
+  %blend = phi i16 [ poison, %loop.header ], [ %iv.trunc.2, %loop.next ]
   %dst.ptr = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i16 %blend
   store i16 0, ptr %dst.ptr
   %iv.next = add nuw nsw i64 %iv, 1
@@ -75,9 +75,9 @@ define void @blend_uniform_iv(i1 %c) {
 ; CHECK:       [[VECTOR_BODY]]:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[PREDPHI:%.*]] = select i1 [[C]], i64 [[TMP0]], i64 undef
-; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i64 [[PREDPHI]]
-; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i16, ptr [[TMP1]], i32 0
+; CHECK-NEXT:    [[TMP6:%.*]] = select i1 [[C]], i64 [[TMP0]], i64 poison
+; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i64 [[TMP6]]
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds i16, ptr [[TMP7]], i32 0
 ; CHECK-NEXT:    store <4 x i16> zeroinitializer, ptr [[TMP2]], align 2
 ; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i64 [[INDEX_NEXT]], 32
@@ -93,7 +93,7 @@ define void @blend_uniform_iv(i1 %c) {
 ; CHECK:       [[LOOP_NEXT]]:
 ; CHECK-NEXT:    br label %[[LOOP_LATCH]]
 ; CHECK:       [[LOOP_LATCH]]:
-; CHECK-NEXT:    [[BLEND:%.*]] = phi i64 [ undef, %[[LOOP_HEADER]] ], [ [[IV]], %[[LOOP_NEXT]] ]
+; CHECK-NEXT:    [[BLEND:%.*]] = phi i64 [ poison, %[[LOOP_HEADER]] ], [ [[IV]], %[[LOOP_NEXT]] ]
 ; CHECK-NEXT:    [[DST_PTR:%.*]] = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i64 [[BLEND]]
 ; CHECK-NEXT:    store i16 0, ptr [[DST_PTR]], align 2
 ; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
@@ -114,7 +114,7 @@ loop.next:                                        ; preds = %loop.header
   br label %loop.latch
 
 loop.latch:                                       ; preds = %loop.next, %loop.header
-  %blend = phi i64 [ undef, %loop.header ], [ %iv, %loop.next ]
+  %blend = phi i64 [ poison, %loop.header ], [ %iv, %loop.next ]
   %dst.ptr = getelementptr inbounds [32 x i16], ptr @dst, i16 0, i64 %blend
   store i16 0, ptr %dst.ptr
   %iv.next = add nuw nsw i64 %iv, 1

diff --git a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -139,7 +139,7 @@ TEST_F(ScalarEvolutionsTest, SimplifiedPHI) {
   auto *Ty = Type::getInt32Ty(Context);
   auto *PN = PHINode::Create(Ty, 2, "", LoopBB->begin());
   PN->addIncoming(Constant::getNullValue(Ty), EntryBB);
-  PN->addIncoming(UndefValue::get(Ty), LoopBB);
+  PN->addIncoming(PoisonValue::get(Ty), LoopBB);
   ScalarEvolution SE = buildSE(*F);
   const SCEV *S1 = SE.getSCEV(PN);
   const SCEV *S2 = SE.getSCEV(PN);

diff --git a/polly/test/CodeGen/OpenMP/floord-as-argument-to-subfunction.ll b/polly/test/CodeGen/OpenMP/floord-as-argument-to-subfunction.ll
@@ -20,9 +20,9 @@ for.cond39.for.cond66.preheader.loopexit67_crit_edge: ; preds = %for.body42
   br label %for.cond66.preheader
 
 for.cond66.preheader:                             ; preds = %for.cond39.for.cond66.preheader.loopexit67_crit_edge, %if.end
-  %rawout1.3.ph = phi ptr [ %add.ptr62.lcssa, %for.cond39.for.cond66.preheader.loopexit67_crit_edge ], [ undef, %if.end ]
+  %rawout1.3.ph = phi ptr [ %add.ptr62.lcssa, %for.cond39.for.cond66.preheader.loopexit67_crit_edge ], [ poison, %if.end ]
   %sb.3.ph = phi i32 [ 0, %for.cond39.for.cond66.preheader.loopexit67_crit_edge ], [ 0, %if.end ]
-  %tspnt.3.ph = phi ptr [ undef, %for.cond39.for.cond66.preheader.loopexit67_crit_edge ], [ %tsOut, %if.end ]
+  %tspnt.3.ph = phi ptr [ poison, %for.cond39.for.cond66.preheader.loopexit67_crit_edge ], [ %tsOut, %if.end ]
   br label %for.cond69.preheader
 
 for.body42:                                       ; preds = %if.end
@@ -31,12 +31,12 @@ for.body42:                                       ; preds = %if.end
 for.cond69.preheader:                             ; preds = %for.end76, %for.cond66.preheader
   %tspnt.375 = phi ptr [ %incdec.ptr79, %for.end76 ], [ %tspnt.3.ph, %for.cond66.preheader ]
   %sb.374 = phi i32 [ %inc78, %for.end76 ], [ %sb.3.ph, %for.cond66.preheader ]
-  %rawout1.373 = phi ptr [ undef, %for.end76 ], [ %rawout1.3.ph, %for.cond66.preheader ]
+  %rawout1.373 = phi ptr [ poison, %for.end76 ], [ %rawout1.3.ph, %for.cond66.preheader ]
   br label %for.body71
 
 for.body71:                                       ; preds = %for.body71, %for.cond69.preheader
   %indvars.iv = phi i64 [ 0, %for.cond69.preheader ], [ %indvars.iv.next, %for.body71 ]
-  %rawout1.469 = phi ptr [ %rawout1.373, %for.cond69.preheader ], [ undef, %for.body71 ]
+  %rawout1.469 = phi ptr [ %rawout1.373, %for.cond69.preheader ], [ poison, %for.body71 ]
   %0 = load i64, ptr %rawout1.469, align 8
   %1 = shl nsw i64 %indvars.iv, 5
   %arrayidx73 = getelementptr inbounds double, ptr %tspnt.375, i64 %1

diff --git a/polly/test/CodeGen/inner_scev_sdiv_2.ll b/polly/test/CodeGen/inner_scev_sdiv_2.ll
@@ -34,7 +34,7 @@ for.cond.60.preheader:                            ; preds = %for.body.51, %for.c
   ret void
 
 for.body.51:                                      ; preds = %for.body.51, %for.body.51.lr.ph
-  %indvars.iv86 = phi i64 [ %2, %for.body.51.lr.ph ], [ undef, %for.body.51 ]
+  %indvars.iv86 = phi i64 [ %2, %for.body.51.lr.ph ], [ poison, %for.body.51 ]
   %arrayidx53 = getelementptr inbounds float, ptr %0, i64 %indvars.iv86
   %3 = load float, ptr %arrayidx53, align 4
   %mul56 = fmul float %3, undef

diff --git a/polly/test/CodeGen/inner_scev_sdiv_3.ll b/polly/test/CodeGen/inner_scev_sdiv_3.ll
@@ -36,7 +36,7 @@ end:
   ret i64 %div44.m
 
 for.body.51:                                      ; preds = %for.body.51, %for.body.51.lr.ph
-  %indvars.iv86 = phi i64 [ %2, %for.body.51.lr.ph ], [ undef, %for.body.51 ]
+  %indvars.iv86 = phi i64 [ %2, %for.body.51.lr.ph ], [ poison, %for.body.51 ]
   %arrayidx53 = getelementptr inbounds float, ptr %0, i64 %indvars.iv86
   %3 = load float, ptr %arrayidx53, align 4
   %mul56 = fmul float %3, undef

diff --git a/polly/test/CodeGen/non-affine-phi-node-expansion.ll b/polly/test/CodeGen/non-affine-phi-node-expansion.ll
@@ -31,7 +31,7 @@ bb1:                                              ; preds = %bb
   br label %bb2
 
 bb2:                                              ; preds = %bb1, %bb
-  %tmp = phi i1 [ true, %bb ], [ undef, %bb1 ]
+  %tmp = phi i1 [ true, %bb ], [ poison, %bb1 ]
   br label %bb3
 
 bb3:                                              ; preds = %bb13, %bb2

diff --git a/polly/test/CodeGen/phi-defined-before-scop.ll b/polly/test/CodeGen/phi-defined-before-scop.ll
@@ -19,7 +19,7 @@ bb:
   br label %bb1
 
 bb1:                                              ; preds = %bb6, %bb
-  %tmp2 = phi ptr [ %tmp7, %bb6 ], [ undef, %bb ]
+  %tmp2 = phi ptr [ %tmp7, %bb6 ], [ poison, %bb ]
   %tmp = load ptr, ptr @global, align 8, !tbaa !1
   br label %bb3
 
@@ -31,7 +31,7 @@ bb5:                                              ; preds = %bb3
   br label %bb6
 
 bb6:                                              ; preds = %bb5, %bb3
-  %tmp7 = phi ptr [ %tmp2, %bb3 ], [ undef, %bb5 ]
+  %tmp7 = phi ptr [ %tmp2, %bb3 ], [ poison, %bb5 ]
   br i1 undef, label %bb8, label %bb1
 
 bb8:                                              ; preds = %bb6

diff --git a/polly/test/CodeGen/scop_expander_insert_point.ll b/polly/test/CodeGen/scop_expander_insert_point.ll
@@ -27,8 +27,8 @@ for.body17.lr.ph:                                 ; preds = %for.end22, %for.con
   br label %for.body17
 
 for.body17:                                       ; preds = %for.body17, %for.body17.lr.ph
-  %outvalue.141 = phi i64 [ undef, %for.body17.lr.ph ], [ %add19, %for.body17 ]
-  %inptr.040 = phi ptr [ %add.ptr, %for.body17.lr.ph ], [ undef, %for.body17 ]
+  %outvalue.141 = phi i64 [ poison, %for.body17.lr.ph ], [ %add19, %for.body17 ]
+  %inptr.040 = phi ptr [ %add.ptr, %for.body17.lr.ph ], [ poison, %for.body17 ]
   %1 = load i8, ptr %inptr.040
   %add19 = mul nsw i64 0, %outvalue.141
   br i1 false, label %for.body17, label %for.end22

diff --git a/polly/test/CodeGen/stack-overflow-in-load-hoisting.ll b/polly/test/CodeGen/stack-overflow-in-load-hoisting.ll
@@ -42,7 +42,7 @@ for.cond.12.preheader.lr.ph:                      ; preds = %entry
   br label %for.body.14.lr.ph
 
 for.body.14.lr.ph:                                ; preds = %for.end, %for.cond.12.preheader.lr.ph
-  %d.050 = phi ptr [ %tmp3, %for.cond.12.preheader.lr.ph ], [ undef, %for.end ]
+  %d.050 = phi ptr [ %tmp3, %for.cond.12.preheader.lr.ph ], [ poison, %for.end ]
   %w = getelementptr inbounds %struct.AudioVectorScopeContext.21.43.879.1209.1297.1319.1573, ptr %s, i32 0, i32 2
   %tmp4 = load i32, ptr %w, align 4
   %cmp13.46 = icmp sgt i32 %tmp4, 0

diff --git a/polly/test/ScopInfo/complex_domain_binary_condition.ll b/polly/test/ScopInfo/complex_domain_binary_condition.ll
@@ -35,7 +35,7 @@ for.body104.lr.ph:                                ; preds = %entry
   br label %for.body104
 
 for.body104:                                      ; preds = %while.end146, %for.body104.lr.ph
-  %indvars.iv = phi i64 [ %6, %for.body104.lr.ph ], [ undef, %while.end146 ]
+  %indvars.iv = phi i64 [ %6, %for.body104.lr.ph ], [ poison, %while.end146 ]
   %7 = sub nsw i64 %indvars.iv, %idx.ext62
   %cmp107 = icmp slt i64 %7, -1
   %.op = xor i64 %7, -1

diff --git a/polly/test/ScopInfo/scev-div-with-evaluatable-divisor.ll b/polly/test/ScopInfo/scev-div-with-evaluatable-divisor.ll
@@ -17,7 +17,7 @@ for.body.lr.ph:                                   ; preds = %entry
   br label %for.body
 
 for.body:                                         ; preds = %for.inc, %for.body.lr.ph
-  %mj.017 = phi i32 [ 1, %for.body.lr.ph ], [ undef, %for.inc ]
+  %mj.017 = phi i32 [ 1, %for.body.lr.ph ], [ poison, %for.inc ]
   br i1 true, label %if.else, label %if.then
 
 if.then:                                          ; preds = %for.body