[llvm] [GVN] Check IndirectBr in Predecessor Terminators (PR #151188)

[via llvm-commits]

https://github.com/ParkHanbum updated https://github.com/llvm/llvm-project/pull/151188

>From 857bd06845c66ad73064135fc8603a541f2526df Mon Sep 17 00:00:00 2001
From: Hanbum Park <kese111 at gmail.com>
Date: Wed, 30 Jul 2025 00:16:51 +0900
Subject: [PATCH] [BreakCritEdges] Check whether IndirectBr is the terminator
 of the block

Critical edges with an IndirectBr terminator cannot be split.
We have already handled it with Assertion, but change it to checking
whether block has IndirectBr terminator.

Fixes : #150229
---
 .../Transforms/Utils/BreakCriticalEdges.cpp   | 11 +++++------
 llvm/test/Transforms/GVN/cond_br.ll           | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp b/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
index ddd203f3acf71..42b1fdf17f389 100644
--- a/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
+++ b/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -111,15 +111,14 @@ BasicBlock *
 llvm::SplitKnownCriticalEdge(Instruction *TI, unsigned SuccNum,
                              const CriticalEdgeSplittingOptions &Options,
                              const Twine &BBName) {
-  assert(!isa<IndirectBrInst>(TI) &&
-         "Cannot split critical edge from IndirectBrInst");
-
   BasicBlock *TIBB = TI->getParent();
   BasicBlock *DestBB = TI->getSuccessor(SuccNum);
 
-  // Splitting the critical edge to a pad block is non-trivial. Don't do
-  // it in this generic function.
-  if (DestBB->isEHPad()) return nullptr;
+  // Splitting the critical edge to a pad block is non-trivial.
+  // And we cannot split block with IndirectBr as a terminator.
+  // Don't do it in this generic function.
+  if (DestBB->isEHPad() || isa<IndirectBrInst>(TI))
+    return nullptr;
 
   if (Options.IgnoreUnreachableDests &&
       isa<UnreachableInst>(DestBB->getFirstNonPHIOrDbgOrLifetime()))
diff --git a/llvm/test/Transforms/GVN/cond_br.ll b/llvm/test/Transforms/GVN/cond_br.ll
index 19166d17a8320..fb84b626c7455 100644
--- a/llvm/test/Transforms/GVN/cond_br.ll
+++ b/llvm/test/Transforms/GVN/cond_br.ll
@@ -53,3 +53,22 @@ if.end:                                           ; preds = %if.else, %if.then
 }
 
 declare void @bar(i32)
+
+define void @indirectbr_could_not_split() {
+; CHECK-LABEL: define void @indirectbr_could_not_split() {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    br i1 false, label %[[IBR:.*]], label %[[EXIT:.*]]
+; CHECK:       [[IBR]]:
+; CHECK-NEXT:    indirectbr ptr null, [label %[[EXIT]], label %exit]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br i1 false, label %ibr, label %exit
+
+ibr:
+  indirectbr ptr null, [label %exit, label %exit]
+
+exit:
+  ret void
+}