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

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport a750fcb52bbf0ec0dc2022f73b1d48a4d43d8a07

Requested by: @<!-- -->nikic

---
Full diff: https://github.com/llvm/llvm-project/pull/152965.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp (+5-6) 
- (modified) llvm/test/Transforms/GVN/cond_br.ll (+19) 


``````````diff
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
+}

``````````

</details>


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