[llvm-branch-commits] [llvm] release/19.x: Bail out jump threading on indirect branches only (#117778) (PR #117869)

[via llvm-branch-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport 3c9022c965b85951f30af140da591f819acef8a0 39601a6e5484de183bf525b7d0624e7890ccd8ab

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

---
Full diff: https://github.com/llvm/llvm-project/pull/117869.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Utils/Local.cpp (+8-2) 
- (added) llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll (+81) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 7192efe3f16b9d..f68cbf62b9825f 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1028,7 +1028,13 @@ CanRedirectPredsOfEmptyBBToSucc(BasicBlock *BB, BasicBlock *Succ,
   if (!BB->hasNPredecessorsOrMore(2))
     return false;
 
-  // Get single common predecessors of both BB and Succ
+  if (any_of(BBPreds, [](const BasicBlock *Pred) {
+        return isa<IndirectBrInst>(Pred->getTerminator());
+      }))
+    return false;
+
+  // Get the single common predecessor of both BB and Succ. Return false
+  // when there are more than one common predecessors.
   for (BasicBlock *SuccPred : SuccPreds) {
     if (BBPreds.count(SuccPred)) {
       if (CommonPred)
@@ -1133,7 +1139,7 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
 
   bool BBKillable = CanPropagatePredecessorsForPHIs(BB, Succ, BBPreds);
 
-  // Even if we can not fold bB into Succ, we may be able to redirect the
+  // Even if we can not fold BB into Succ, we may be able to redirect the
   // predecessors of BB to Succ.
   bool BBPhisMergeable =
       BBKillable ||
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll b/llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll
new file mode 100644
index 00000000000000..d3713be8358db4
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/switch-branch-fold-indirectbr-102351.ll
@@ -0,0 +1,81 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --prefix-filecheck-ir-name pref --version 5
+; RUN: opt < %s -passes=simplifycfg -S | FileCheck %s
+
+define i32 @foo.1(i32 %arg, ptr %arg1) {
+; CHECK-LABEL: define i32 @foo.1(
+; CHECK-SAME: i32 [[ARG:%.*]], ptr [[ARG1:%.*]]) {
+; CHECK-NEXT:  [[BB:.*]]:
+; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [2 x ptr], align 16
+; CHECK-NEXT:    store ptr blockaddress(@foo.1, %[[BB8:.*]]), ptr [[ALLOCA]], align 16
+; CHECK-NEXT:    [[GETELEMENTPTR:%.*]] = getelementptr inbounds [2 x ptr], ptr [[ALLOCA]], i64 0, i64 1
+; CHECK-NEXT:    store ptr blockaddress(@foo.1, %[[BB16:.*]]), ptr [[GETELEMENTPTR]], align 8
+; CHECK-NEXT:    br label %[[PREFBB2:.*]]
+; CHECK:       [[PREFBB2]]:
+; CHECK-NEXT:    [[PHI:%.*]] = phi i32 [ 0, %[[BB]] ], [ [[PHI14:%.*]], %[[BB13:.*]] ]
+; CHECK-NEXT:    [[PHI3:%.*]] = phi i32 [ 0, %[[BB]] ], [ [[PHI15:%.*]], %[[BB13]] ]
+; CHECK-NEXT:    switch i32 [[PHI]], label %[[BB13]] [
+; CHECK-NEXT:      i32 0, label %[[PREFBB18:.*]]
+; CHECK-NEXT:      i32 1, label %[[BB8]]
+; CHECK-NEXT:      i32 2, label %[[PREFBB11:.*]]
+; CHECK-NEXT:    ]
+; CHECK:       [[BB8]]:
+; CHECK-NEXT:    [[PHI10:%.*]] = phi i32 [ [[ARG]], %[[PREFBB18]] ], [ [[PHI3]], %[[PREFBB2]] ]
+; CHECK-NEXT:    br label %[[BB13]]
+; CHECK:       [[PREFBB11]]:
+; CHECK-NEXT:    [[CALL:%.*]] = call i32 @wombat(i32 noundef [[PHI3]])
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[PHI3]], 1
+; CHECK-NEXT:    br label %[[PREFBB18]]
+; CHECK:       [[BB13]]:
+; CHECK-NEXT:    [[PHI14]] = phi i32 [ [[PHI]], %[[PREFBB2]] ], [ 2, %[[BB8]] ]
+; CHECK-NEXT:    [[PHI15]] = phi i32 [ [[PHI3]], %[[PREFBB2]] ], [ [[PHI10]], %[[BB8]] ]
+; CHECK-NEXT:    br label %[[PREFBB2]]
+; CHECK:       [[BB16]]:
+; CHECK-NEXT:    [[CALL17:%.*]] = call i32 @wombat(i32 noundef [[ARG]])
+; CHECK-NEXT:    ret i32 0
+; CHECK:       [[PREFBB18]]:
+; CHECK-NEXT:    [[LOAD:%.*]] = load ptr, ptr [[ARG1]], align 8
+; CHECK-NEXT:    indirectbr ptr [[LOAD]], [label %[[BB8]], label %bb16]
+;
+bb:
+  %alloca = alloca [2 x ptr], align 16
+  store ptr blockaddress(@foo.1, %bb8), ptr %alloca, align 16
+  %getelementptr = getelementptr inbounds [2 x ptr], ptr %alloca, i64 0, i64 1
+  store ptr blockaddress(@foo.1, %bb16), ptr %getelementptr, align 8
+  br label %bb2
+
+bb2:                                              ; preds = %bb13, %bb
+  %phi = phi i32 [ 0, %bb ], [ %phi14, %bb13 ]
+  %phi3 = phi i32 [ 0, %bb ], [ %phi15, %bb13 ]
+  switch i32 %phi, label %bb13 [
+  i32 0, label %bb5
+  i32 1, label %bb8
+  i32 2, label %bb11
+  ]
+
+bb5:                                              ; preds = %bb2
+  br label %bb18
+
+bb8:                                              ; preds = %bb18, %bb2
+  %phi10 = phi i32 [ %arg, %bb18 ], [ %phi3, %bb2 ]
+  br label %bb13
+
+bb11:                                             ; preds = %bb2
+  %call = call i32 @wombat(i32 noundef %phi3)
+  %add = add nsw i32 %phi3, 1
+  br label %bb18
+
+bb13:                                             ; preds = %bb8, %bb2
+  %phi14 = phi i32 [ %phi, %bb2 ], [ 2, %bb8 ]
+  %phi15 = phi i32 [ %phi3, %bb2 ], [ %phi10, %bb8 ]
+  br label %bb2
+
+bb16:                                             ; preds = %bb18
+  %call17 = call i32 @wombat(i32 noundef %arg)
+  ret i32 0
+
+bb18:                                             ; preds = %bb11, %bb5
+  %load = load ptr, ptr %arg1, align 8
+  indirectbr ptr %load, [label %bb8, label %bb16]
+}
+
+declare i32 @wombat(i32)

``````````

</details>


https://github.com/llvm/llvm-project/pull/117869