[SimplifyCFG] Allow some switch optimizations early in the pipeline

llvm/include/llvm/Transforms/Utils/SimplifyCFGOptions.h

@@ -24,6 +24,7 @@ struct SimplifyCFGOptions {
   int BonusInstThreshold = 1;
   bool ForwardSwitchCondToPhi = false;
   bool ConvertSwitchRangeToICmp = false;
+  bool ConvertSwitchToArithmetic = false;
   bool ConvertSwitchToLookupTable = false;
   bool NeedCanonicalLoop = true;
   bool HoistCommonInsts = false;
@@ -48,6 +49,10 @@ struct SimplifyCFGOptions {
     ConvertSwitchRangeToICmp = B;
     return *this;
   }
+  SimplifyCFGOptions &convertSwitchToArithmetic(bool B) {
+    ConvertSwitchToArithmetic = B;
+    return *this;
+  }
   SimplifyCFGOptions &convertSwitchToLookupTable(bool B) {
     ConvertSwitchToLookupTable = B;
     return *this;

llvm/lib/Passes/PassBuilder.cpp

@@ -1017,6 +1017,8 @@ Expected<SimplifyCFGOptions> parseSimplifyCFGOptions(StringRef Params) {
       Result.forwardSwitchCondToPhi(Enable);
     } else if (ParamName == "switch-range-to-icmp") {
       Result.convertSwitchRangeToICmp(Enable);
+    } else if (ParamName == "switch-to-arithmetic") {
+      Result.convertSwitchToArithmetic(Enable);
     } else if (ParamName == "switch-to-lookup") {
       Result.convertSwitchToLookupTable(Enable);
     } else if (ParamName == "keep-loops") {

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -775,6 +775,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
 
   FPM.addPass(SimplifyCFGPass(SimplifyCFGOptions()
                                   .convertSwitchRangeToICmp(true)
+                                  .convertSwitchToArithmetic(true)
                                   .hoistCommonInsts(true)
                                   .sinkCommonInsts(true)));
   FPM.addPass(InstCombinePass());
@@ -1372,6 +1373,7 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
   FPM.addPass(SimplifyCFGPass(SimplifyCFGOptions()
                                   .forwardSwitchCondToPhi(true)
                                   .convertSwitchRangeToICmp(true)
+                                  .convertSwitchToArithmetic(true)
                                   .convertSwitchToLookupTable(true)
                                   .needCanonicalLoops(false)
                                   .hoistCommonInsts(true)
@@ -1588,6 +1590,7 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
   OptimizePM.addPass(
       SimplifyCFGPass(SimplifyCFGOptions()
                           .convertSwitchRangeToICmp(true)
+                          .convertSwitchToArithmetic(true)
                           .speculateUnpredictables(true)
                           .hoistLoadsStoresWithCondFaulting(true)));
 
@@ -2172,6 +2175,7 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
   // Delete basic blocks, which optimization passes may have killed.
   LateFPM.addPass(SimplifyCFGPass(SimplifyCFGOptions()
                                       .convertSwitchRangeToICmp(true)
+                                      .convertSwitchToArithmetic(true)
                                       .hoistCommonInsts(true)
                                       .speculateUnpredictables(true)));
   MPM.addPass(createModuleToFunctionPassAdaptor(std::move(LateFPM)));
@@ -2355,4 +2359,4 @@ AAManager PassBuilder::buildDefaultAAPipeline() {
 bool PassBuilder::isInstrumentedPGOUse() const {
   return (PGOOpt && PGOOpt->Action == PGOOptions::IRUse) ||
          !UseCtxProfile.empty();
-}
+}

llvm/lib/Passes/PassRegistry.def

@@ -684,8 +684,9 @@ FUNCTION_PASS_WITH_PARAMS(
     parseSimplifyCFGOptions,
     "no-speculate-blocks;speculate-blocks;no-simplify-cond-branch;"
     "simplify-cond-branch;no-forward-switch-cond;forward-switch-cond;"
-    "no-switch-range-to-icmp;switch-range-to-icmp;no-switch-to-lookup;"
-    "switch-to-lookup;no-keep-loops;keep-loops;no-hoist-common-insts;"
+    "no-switch-range-to-icmp;switch-range-to-icmp;no-switch-to-arithmetic;"
+    "switch-to-arithmetic;no-switch-to-lookup;switch-to-lookup;"
+    "no-keep-loops;keep-loops;no-hoist-common-insts;"
     "hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;"
     "hoist-loads-stores-with-cond-faulting;no-sink-common-insts;"
     "sink-common-insts;no-speculate-unpredictables;speculate-unpredictables;"

llvm/lib/Transforms/Scalar/SimplifyCFGPass.cpp

@@ -355,6 +355,8 @@ void SimplifyCFGPass::printPipeline(
   OS << (Options.ForwardSwitchCondToPhi ? "" : "no-") << "forward-switch-cond;";
   OS << (Options.ConvertSwitchRangeToICmp ? "" : "no-")
      << "switch-range-to-icmp;";
+  OS << (Options.ConvertSwitchToArithmetic ? "" : "no-")
+     << "switch-to-arithmetic;";
   OS << (Options.ConvertSwitchToLookupTable ? "" : "no-")
      << "switch-to-lookup;";
   OS << (Options.NeedCanonicalLoop ? "" : "no-") << "keep-loops;";

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -6508,6 +6508,9 @@ class SwitchReplacement {
   /// Return true if the replacement is a lookup table.
   bool isLookupTable();
 
+  /// Return true if the replacement is a bit map.
+  bool isBitMap();
+
 private:
   // Depending on the switch, there are different alternatives.
   enum {
@@ -6798,6 +6801,8 @@ Constant *SwitchReplacement::getDefaultValue() { return DefaultValue; }
 
 bool SwitchReplacement::isLookupTable() { return Kind == LookupTableKind; }
 
+bool SwitchReplacement::isBitMap() { return Kind == BitMapKind; }
+
 static bool isSwitchDense(uint64_t NumCases, uint64_t CaseRange) {
   // 40% is the default density for building a jump table in optsize/minsize
   // mode. See also TargetLoweringBase::isSuitableForJumpTable(), which this
@@ -6963,7 +6968,8 @@ static void reuseTableCompare(
 /// lookup tables.
 static bool simplifySwitchLookup(SwitchInst *SI, IRBuilder<> &Builder,
                                  DomTreeUpdater *DTU, const DataLayout &DL,
-                                 const TargetTransformInfo &TTI) {
+                                 const TargetTransformInfo &TTI,
+                                 bool ConvertSwitchToLookupTable) {
   assert(SI->getNumCases() > 1 && "Degenerate switch?");
 
   BasicBlock *BB = SI->getParent();
@@ -7128,6 +7134,8 @@ static bool simplifySwitchLookup(SwitchInst *SI, IRBuilder<> &Builder,
 
   bool AnyLookupTables = any_of(
       PhiToReplacementMap, [](auto &KV) { return KV.second.isLookupTable(); });
+  bool AnyBitMaps = any_of(PhiToReplacementMap,
+                           [](auto &KV) { return KV.second.isBitMap(); });
 
   // A few conditions prevent the generation of lookup tables:
   //     1. The target does not support lookup tables.
@@ -7140,6 +7148,12 @@ static bool simplifySwitchLookup(SwitchInst *SI, IRBuilder<> &Builder,
        Fn->getFnAttribute("no-jump-tables").getValueAsBool()))
     return false;
 
+  // In the early optimization pipeline, disable formation of lookup tables,
+  // bit maps and mask checks, as they may inhibit further optimization.
+  if (!ConvertSwitchToLookupTable &&
+      (AnyLookupTables || AnyBitMaps || NeedMask))
+    return false;
+
   Builder.SetInsertPoint(SI);
   // TableIndex is the switch condition - TableIndexOffset if we don't
   // use the condition directly
@@ -7780,14 +7794,10 @@ bool SimplifyCFGOpt::simplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
   if (Options.ForwardSwitchCondToPhi && forwardSwitchConditionToPHI(SI))
     return requestResimplify();
 
-  // The conversion from switch to lookup tables results in difficult-to-analyze
-  // code and makes pruning branches much harder. This is a problem if the
-  // switch expression itself can still be restricted as a result of inlining or
-  // CVP. Therefore, only apply this transformation during late stages of the
-  // optimisation pipeline.
-  if (Options.ConvertSwitchToLookupTable &&
-      simplifySwitchLookup(SI, Builder, DTU, DL, TTI))
-    return requestResimplify();
+  if (Options.ConvertSwitchToArithmetic || Options.ConvertSwitchToLookupTable)
+    if (simplifySwitchLookup(SI, Builder, DTU, DL, TTI,
+                             Options.ConvertSwitchToLookupTable))
+      return requestResimplify();
 
   if (simplifySwitchOfPowersOfTwo(SI, Builder, DL, TTI))
     return requestResimplify();

llvm/test/Other/new-pm-print-pipeline.ll

@@ -50,7 +50,7 @@
 ; CHECK-17: function(print<stack-lifetime><may>,print<stack-lifetime><must>)
 
 ; RUN: opt -disable-output -disable-verify -print-pipeline-passes -passes='function(simplifycfg<bonus-inst-threshold=5;forward-switch-cond;switch-to-lookup;keep-loops;hoist-common-insts;hoist-loads-stores-with-cond-faulting;sink-common-insts;speculate-blocks;simplify-cond-branch;speculate-unpredictables>,simplifycfg<bonus-inst-threshold=7;no-forward-switch-cond;no-switch-to-lookup;no-keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;no-speculate-blocks;no-simplify-cond-branch;no-speculate-unpredictables>)' < %s | FileCheck %s --match-full-lines --check-prefixes=CHECK-18
-; CHECK-18: function(simplifycfg<bonus-inst-threshold=5;forward-switch-cond;no-switch-range-to-icmp;switch-to-lookup;keep-loops;hoist-common-insts;hoist-loads-stores-with-cond-faulting;sink-common-insts;speculate-blocks;simplify-cond-branch;speculate-unpredictables>,simplifycfg<bonus-inst-threshold=7;no-forward-switch-cond;no-switch-range-to-icmp;no-switch-to-lookup;no-keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;no-speculate-blocks;no-simplify-cond-branch;no-speculate-unpredictables>)
+; CHECK-18: function(simplifycfg<bonus-inst-threshold=5;forward-switch-cond;no-switch-range-to-icmp;no-switch-to-arithmetic;switch-to-lookup;keep-loops;hoist-common-insts;hoist-loads-stores-with-cond-faulting;sink-common-insts;speculate-blocks;simplify-cond-branch;speculate-unpredictables>,simplifycfg<bonus-inst-threshold=7;no-forward-switch-cond;no-switch-range-to-icmp;no-switch-to-arithmetic;no-switch-to-lookup;no-keep-loops;no-hoist-common-insts;no-hoist-loads-stores-with-cond-faulting;no-sink-common-insts;no-speculate-blocks;no-simplify-cond-branch;no-speculate-unpredictables>)
 
 ; RUN: opt -disable-output -disable-verify -print-pipeline-passes -passes='function(loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only>,loop-vectorize<interleave-forced-only;vectorize-forced-only>)' < %s | FileCheck %s --match-full-lines --check-prefixes=CHECK-19
 ; CHECK-19: function(loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only;>,loop-vectorize<interleave-forced-only;vectorize-forced-only;>)

llvm/test/Transforms/SimplifyCFG/switch-transformations-no-lut.ll

@@ -1,29 +1,17 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
-; RUN: opt -S -passes='simplifycfg' < %s | FileCheck %s --check-prefix=OPTNOLUT
+; RUN: opt -S -passes='simplifycfg<switch-to-arithmetic>' < %s | FileCheck %s --check-prefix=OPTNOLUT
 ; RUN: %if amdgpu-registered-target %{ opt -mtriple=amdgcn--amdpal -S -passes='simplifycfg<switch-to-lookup>' < %s | FileCheck %s --check-prefix=TTINOLUT %}
 ;
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 
 define i32 @linear_transform_with_default(i32 %x) {
 ; OPTNOLUT-LABEL: define i32 @linear_transform_with_default(
 ; OPTNOLUT-SAME: i32 [[X:%.*]]) {
-; OPTNOLUT-NEXT:  [[ENTRY:.*]]:
-; OPTNOLUT-NEXT:    switch i32 [[X]], label %[[END:.*]] [
-; OPTNOLUT-NEXT:      i32 0, label %[[CASE0:.*]]
-; OPTNOLUT-NEXT:      i32 1, label %[[CASE1:.*]]
-; OPTNOLUT-NEXT:      i32 2, label %[[CASE2:.*]]
-; OPTNOLUT-NEXT:      i32 3, label %[[CASE3:.*]]
-; OPTNOLUT-NEXT:    ]
-; OPTNOLUT:       [[CASE0]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[CASE1]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[CASE2]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[CASE3]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[END]]:
-; OPTNOLUT-NEXT:    [[IDX:%.*]] = phi i32 [ 1, %[[CASE0]] ], [ 4, %[[CASE1]] ], [ 7, %[[CASE2]] ], [ 10, %[[CASE3]] ], [ 13, %[[ENTRY]] ]
+; OPTNOLUT-NEXT:  [[ENTRY:.*:]]
+; OPTNOLUT-NEXT:    [[TMP0:%.*]] = icmp ult i32 [[X]], 4
+; OPTNOLUT-NEXT:    [[SWITCH_IDX_MULT:%.*]] = mul nsw i32 [[X]], 3
+; OPTNOLUT-NEXT:    [[SWITCH_OFFSET:%.*]] = add nsw i32 [[SWITCH_IDX_MULT]], 1
+; OPTNOLUT-NEXT:    [[IDX:%.*]] = select i1 [[TMP0]], i32 [[SWITCH_OFFSET]], i32 13
 ; OPTNOLUT-NEXT:    ret i32 [[IDX]]
 ;
 ; TTINOLUT-LABEL: define i32 @linear_transform_with_default(
@@ -138,26 +126,8 @@ end:
 define i32 @linear_transform_no_default(i32 %x) {
 ; OPTNOLUT-LABEL: define i32 @linear_transform_no_default(
 ; OPTNOLUT-SAME: i32 [[X:%.*]]) {
-; OPTNOLUT-NEXT:  [[ENTRY:.*]]:
-; OPTNOLUT-NEXT:    switch i32 [[X]], label %[[DEFAULT:.*]] [
-; OPTNOLUT-NEXT:      i32 0, label %[[END:.*]]
-; OPTNOLUT-NEXT:      i32 1, label %[[CASE1:.*]]
-; OPTNOLUT-NEXT:      i32 2, label %[[CASE2:.*]]
-; OPTNOLUT-NEXT:      i32 3, label %[[CASE3:.*]]
-; OPTNOLUT-NEXT:      i32 4, label %[[CASE4:.*]]
-; OPTNOLUT-NEXT:    ]
-; OPTNOLUT:       [[CASE1]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[CASE2]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[CASE3]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[CASE4]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[DEFAULT]]:
-; OPTNOLUT-NEXT:    unreachable
-; OPTNOLUT:       [[END]]:
-; OPTNOLUT-NEXT:    [[SWITCH_IDX_MULT:%.*]] = phi i32 [ 3, %[[CASE1]] ], [ 6, %[[CASE2]] ], [ 9, %[[CASE3]] ], [ 12, %[[CASE4]] ], [ 0, %[[ENTRY]] ]
+; OPTNOLUT-NEXT:  [[ENTRY:.*:]]
+; OPTNOLUT-NEXT:    [[SWITCH_IDX_MULT:%.*]] = mul nsw i32 [[X]], 3
 ; OPTNOLUT-NEXT:    ret i32 [[SWITCH_IDX_MULT]]
 ;
 ; TTINOLUT-LABEL: define i32 @linear_transform_no_default(
@@ -350,18 +320,9 @@ end:
 define i32 @single_value_withdefault(i32 %x) {
 ; OPTNOLUT-LABEL: define i32 @single_value_withdefault(
 ; OPTNOLUT-SAME: i32 [[X:%.*]]) {
-; OPTNOLUT-NEXT:  [[ENTRY:.*]]:
-; OPTNOLUT-NEXT:    switch i32 [[X]], label %[[DEFAULT:.*]] [
-; OPTNOLUT-NEXT:      i32 0, label %[[END:.*]]
-; OPTNOLUT-NEXT:      i32 1, label %[[END]]
-; OPTNOLUT-NEXT:      i32 2, label %[[END]]
-; OPTNOLUT-NEXT:      i32 3, label %[[END]]
-; OPTNOLUT-NEXT:      i32 4, label %[[END]]
-; OPTNOLUT-NEXT:    ]
-; OPTNOLUT:       [[DEFAULT]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[END]]:
-; OPTNOLUT-NEXT:    [[DOT:%.*]] = phi i32 [ 3, %[[DEFAULT]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ]
+; OPTNOLUT-NEXT:  [[ENTRY:.*:]]
+; OPTNOLUT-NEXT:    [[TMP0:%.*]] = icmp ult i32 [[X]], 5
+; OPTNOLUT-NEXT:    [[DOT:%.*]] = select i1 [[TMP0]], i32 2, i32 3
 ; OPTNOLUT-NEXT:    ret i32 [[DOT]]
 ;
 ; TTINOLUT-LABEL: define i32 @single_value_withdefault(
@@ -401,18 +362,9 @@ end:
 define i32 @single_value_no_jump_tables(i32 %x) "no-jump-tables"="true" {
 ; OPTNOLUT-LABEL: define i32 @single_value_no_jump_tables(
 ; OPTNOLUT-SAME: i32 [[X:%.*]]) #[[ATTR0:[0-9]+]] {
-; OPTNOLUT-NEXT:  [[ENTRY:.*]]:
-; OPTNOLUT-NEXT:    switch i32 [[X]], label %[[DEFAULT:.*]] [
-; OPTNOLUT-NEXT:      i32 0, label %[[END:.*]]
-; OPTNOLUT-NEXT:      i32 1, label %[[END]]
-; OPTNOLUT-NEXT:      i32 2, label %[[END]]
-; OPTNOLUT-NEXT:      i32 3, label %[[END]]
-; OPTNOLUT-NEXT:      i32 4, label %[[END]]
-; OPTNOLUT-NEXT:    ]
-; OPTNOLUT:       [[DEFAULT]]:
-; OPTNOLUT-NEXT:    br label %[[END]]
-; OPTNOLUT:       [[END]]:
-; OPTNOLUT-NEXT:    [[IDX:%.*]] = phi i32 [ 3, %[[DEFAULT]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ], [ 2, %[[ENTRY]] ]
+; OPTNOLUT-NEXT:  [[ENTRY:.*:]]
+; OPTNOLUT-NEXT:    [[TMP0:%.*]] = icmp ult i32 [[X]], 5
+; OPTNOLUT-NEXT:    [[IDX:%.*]] = select i1 [[TMP0]], i32 2, i32 3
 ; OPTNOLUT-NEXT:    ret i32 [[IDX]]
 ;
 ; TTINOLUT-LABEL: define i32 @single_value_no_jump_tables(
@@ -449,6 +401,60 @@ end:
   ret i32 %idx
 }
 
+define i1 @single_value_with_mask(i32 %x) {
+; OPTNOLUT-LABEL: define i1 @single_value_with_mask(
+; OPTNOLUT-SAME: i32 [[X:%.*]]) {
+; OPTNOLUT-NEXT:  [[ENTRY:.*]]:
+; OPTNOLUT-NEXT:    switch i32 [[X]], label %[[DEFAULT:.*]] [
+; OPTNOLUT-NEXT:      i32 18, label %[[END:.*]]
+; OPTNOLUT-NEXT:      i32 21, label %[[END]]
+; OPTNOLUT-NEXT:      i32 48, label %[[END]]
+; OPTNOLUT-NEXT:      i32 16, label %[[END]]
+; OPTNOLUT-NEXT:    ]
+; OPTNOLUT:       [[DEFAULT]]:
+; OPTNOLUT-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X]], 80
+; OPTNOLUT-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i1 false, i1 true
+; OPTNOLUT-NEXT:    br label %[[END]]
+; OPTNOLUT:       [[END]]:
+; OPTNOLUT-NEXT:    [[RES:%.*]] = phi i1 [ false, %[[ENTRY]] ], [ false, %[[ENTRY]] ], [ false, %[[ENTRY]] ], [ false, %[[ENTRY]] ], [ [[SEL]], %[[DEFAULT]] ]
+; OPTNOLUT-NEXT:    ret i1 [[RES]]
+;
+; TTINOLUT-LABEL: define i1 @single_value_with_mask(
+; TTINOLUT-SAME: i32 [[X:%.*]]) {
+; TTINOLUT-NEXT:  [[ENTRY:.*]]:
+; TTINOLUT-NEXT:    [[SWITCH_TABLEIDX:%.*]] = sub i32 [[X]], 16
+; TTINOLUT-NEXT:    [[TMP0:%.*]] = icmp ult i32 [[SWITCH_TABLEIDX]], 33
+; TTINOLUT-NEXT:    [[SWITCH_MASKINDEX:%.*]] = zext i32 [[SWITCH_TABLEIDX]] to i64
+; TTINOLUT-NEXT:    [[SWITCH_SHIFTED:%.*]] = lshr i64 4294967333, [[SWITCH_MASKINDEX]]
+; TTINOLUT-NEXT:    [[SWITCH_LOBIT:%.*]] = trunc i64 [[SWITCH_SHIFTED]] to i1
+; TTINOLUT-NEXT:    [[OR_COND:%.*]] = select i1 [[TMP0]], i1 [[SWITCH_LOBIT]], i1 false
+; TTINOLUT-NEXT:    br i1 [[OR_COND]], label %[[END:.*]], label %[[DEFAULT:.*]]
+; TTINOLUT:       [[DEFAULT]]:
+; TTINOLUT-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X]], 80
+; TTINOLUT-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i1 false, i1 true
+; TTINOLUT-NEXT:    br label %[[END]]
+; TTINOLUT:       [[END]]:
+; TTINOLUT-NEXT:    [[RES:%.*]] = phi i1 [ [[SEL]], %[[DEFAULT]] ], [ false, %[[ENTRY]] ]
+; TTINOLUT-NEXT:    ret i1 [[RES]]
+;
+entry:
+  switch i32 %x, label %default [
+  i32 18, label %end
+  i32 21, label %end
+  i32 48, label %end
+  i32 16, label %end
+  ]
+
+default:
+  %cmp = icmp eq i32 %x, 80
+  %sel = select i1 %cmp, i1 false, i1 true
+  br label %end
+
+end:
+  %res = phi i1 [ false, %entry ], [ false, %entry ], [ false, %entry ], [ false, %entry ], [ %sel, %default ]
+  ret i1 %res
+}
+
 define i32 @lookup_table(i32 %x) {
 ; OPTNOLUT-LABEL: define i32 @lookup_table(
 ; OPTNOLUT-SAME: i32 [[X:%.*]]) {