[llvm-branch-commits] [llvm] release/21.x: [GVN] Check IndirectBr in Predecessor Terminators (#151188) (PR #152965)

[Tobias Hieta via llvm-branch-commits]

https://github.com/tru updated https://github.com/llvm/llvm-project/pull/152965

>From 6f5c887e557ff6baa98c871541e6b901de211739 Mon Sep 17 00:00:00 2001
From: hanbeom <kese111 at gmail.com>
Date: Mon, 11 Aug 2025 16:25:52 +0900
Subject: [PATCH] [GVN] Check IndirectBr in Predecessor Terminators (#151188)

Critical edges with an IndirectBr terminator cannot be split.
Add a check it to prevent assertion failures.

Fixes: #150229
(cherry picked from commit a750fcb52bbf0ec0dc2022f73b1d48a4d43d8a07)
---
 .../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
+}