[llvm] [IR][NFC] Use `SwitchInst::defaultDestUndefined` (PR #134199)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/134199

None

>From 36e372d05f8dcfb1ef9b9eafbd402e7c346c490b Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Thu, 3 Apr 2025 13:07:34 +0800
Subject: [PATCH] [IR][NFC] Use `SwitchInst::defaultDestUndefined`

---
 .../Scalar/CorrelatedValuePropagation.cpp           |  5 ++---
 llvm/lib/Transforms/Utils/Local.cpp                 |  4 +---
 llvm/lib/Transforms/Utils/LowerSwitch.cpp           |  2 +-
 llvm/lib/Transforms/Utils/SimplifyCFG.cpp           | 13 ++++---------
 4 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 314a5d15f0f88..eadf7d7cd89ca 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -410,9 +410,8 @@ static bool processSwitch(SwitchInst *I, LazyValueInfo *LVI,
       ++ReachableCaseCount;
     }
 
-    BasicBlock *DefaultDest = SI->getDefaultDest();
-    if (ReachableCaseCount > 1 &&
-        !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())) {
+    if (ReachableCaseCount > 1 && !SI->defaultDestUndefined()) {
+      BasicBlock *DefaultDest = SI->getDefaultDest();
       ConstantRange CR = LVI->getConstantRangeAtUse(I->getOperandUse(0),
                                                     /*UndefAllowed*/ false);
       // The default dest is unreachable if all cases are covered.
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 95f0d099aacb5..69acc19605872 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -203,10 +203,8 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
     BasicBlock *TheOnlyDest = DefaultDest;
 
     // If the default is unreachable, ignore it when searching for TheOnlyDest.
-    if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
-        SI->getNumCases() > 0) {
+    if (SI->defaultDestUndefined() && SI->getNumCases() > 0)
       TheOnlyDest = SI->case_begin()->getCaseSuccessor();
-    }
 
     bool Changed = false;
 
diff --git a/llvm/lib/Transforms/Utils/LowerSwitch.cpp b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
index c1999fed44296..7d3226bf6b6bd 100644
--- a/llvm/lib/Transforms/Utils/LowerSwitch.cpp
+++ b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
@@ -388,7 +388,7 @@ void ProcessSwitchInst(SwitchInst *SI,
   ConstantInt *UpperBound = nullptr;
   bool DefaultIsUnreachableFromSwitch = false;
 
-  if (isa<UnreachableInst>(Default->getFirstNonPHIOrDbg())) {
+  if (SI->defaultDestUndefined()) {
     // Make the bounds tightly fitted around the case value range, because we
     // know that the value passed to the switch must be exactly one of the case
     // values.
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 998677af3411e..099c1ffe91e60 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5715,8 +5715,7 @@ bool SimplifyCFGOpt::turnSwitchRangeIntoICmp(SwitchInst *SI,
                                              IRBuilder<> &Builder) {
   assert(SI->getNumCases() > 1 && "Degenerate switch?");
 
-  bool HasDefault =
-      !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
+  bool HasDefault = !SI->defaultDestUndefined();
 
   auto *BB = SI->getParent();
 
@@ -5879,8 +5878,7 @@ static bool eliminateDeadSwitchCases(SwitchInst *SI, DomTreeUpdater *DTU,
   // default destination becomes dead and we can remove it.  If we know some
   // of the bits in the value, we can use that to more precisely compute the
   // number of possible unique case values.
-  bool HasDefault =
-      !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
+  bool HasDefault = !SI->defaultDestUndefined();
   const unsigned NumUnknownBits =
       Known.getBitWidth() - (Known.Zero | Known.One).popcount();
   assert(NumUnknownBits <= Known.getBitWidth());
@@ -6237,11 +6235,8 @@ static bool initializeUniqueCases(SwitchInst *SI, PHINode *&PHI,
   // is unreachable.
   DefaultResult =
       DefaultResults.size() == 1 ? DefaultResults.begin()->second : nullptr;
-  if ((!DefaultResult &&
-       !isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg())))
-    return false;
 
-  return true;
+  return DefaultResult || SI->defaultDestUndefined();
 }
 
 // Helper function that checks if it is possible to transform a switch with only
@@ -7281,7 +7276,7 @@ static bool simplifySwitchOfPowersOfTwo(SwitchInst *SI, IRBuilder<> &Builder,
   // We perform this optimization only for switches with
   // unreachable default case.
   // This assumtion will save us from checking if `Condition` is a power of two.
-  if (!isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg()))
+  if (!SI->defaultDestUndefined())
     return false;
 
   // Check that switch cases are powers of two.