[LoopRotate] processLoop should return true even if it just simplified the loop latch without making any other changes

Simplifying a loop latch changes the IR and we need to make sure the pass manager knows to invalidate analysis passes if that happened.

PR35210 discovered a case where we failed to invalidate the post dominator tree after this simplification because we no changes other than simplifying the loop latch.

Fixes PR35210.

Differential Revision: https://reviews.llvm.org/D40035

llvm-svn: 318237

2 files changed, 71 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 2f8dfaee7c5..a91f53ba663 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -634,7 +634,7 @@ bool LoopRotate::processLoop(Loop *L) {
   if ((MadeChange || SimplifiedLatch) && LoopMD)
     L->setLoopID(LoopMD);
 
-  return MadeChange;
+  return MadeChange || SimplifiedLatch;
 }
 
 LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
diff --git a/llvm/test/Transforms/LoopRotate/pr35210.ll b/llvm/test/Transforms/LoopRotate/pr35210.ll
new file mode 100644
index 00000000000..ea7dfe56074
--- /dev/null
+++ b/llvm/test/Transforms/LoopRotate/pr35210.ll
@@ -0,0 +1,70 @@
+;RUN: opt %s -passes='adce,loop(rotate),adce' -S -debug-pass-manager -debug-only=loop-rotate 2>&1 | FileCheck %s
+
+; This test is to make sure we invalidate the post dominator pass after loop rotate simplifies the loop latch.
+; The adce passes are here to make sure post dominator analysis is required.
+
+; CHECK: Starting llvm::Function pass manager run.
+; CHECK-NEXT: Running pass: ADCEPass on f
+; CHECK-NEXT: Running analysis: DominatorTreeAnalysis on f
+; CHECK-NEXT: Running analysis: PostDominatorTreeAnalysis on f
+; CHECK-NEXT: Running pass: FunctionToLoopPassAdaptor{{.*}} on f
+; CHECK-NEXT: Running analysis: LoopAnalysis on f
+; CHECK-NEXT: Running analysis: AssumptionAnalysis on f
+; CHECK-NEXT: Running analysis: AAManager on f
+; CHECK-NEXT: Running analysis: TargetLibraryAnalysis on f
+; CHECK-NEXT: Running analysis: ScalarEvolutionAnalysis on f
+; CHECK-NEXT: Running analysis: TargetIRAnalysis on f
+; CHECK-NEXT: Running analysis: InnerAnalysisManagerProxy{{.*}} on f
+; CHECK-NEXT: Starting Loop pass manager run.
+; CHECK-NEXT: Running pass: LoopRotatePass on Loop at depth 1 containing: %bb<header><exiting>,%bb4<latch>
+; CHECK-NEXT: Folding loop latch bb4 into bb
+; CHECK-NEXT: Invalidating all non-preserved analyses for: bb
+; CHECK-NEXT: Finished Loop pass manager run.
+; CHECK-NEXT: Invalidating all non-preserved analyses for: f
+; CHECK-NEXT: Invalidating analysis: PostDominatorTreeAnalysis on f
+; CHECK-NEXT: Running pass: ADCEPass on f
+; CHECK-NEXT: Running analysis: PostDominatorTreeAnalysis on f
+; CHECK-NEXT: Finished llvm::Function pass manager run.
+
+; CHECK-LABEL: define i8 @f() {
+; CHECK-NEXT : entry:
+; CHECK-NEXT :   br label %bb
+; CHECK-NEXT :
+; CHECK-NEXT : bb:                                               ; preds = %bb, %entry
+; CHECK-NEXT :   %mode.0 = phi i8 [ 0, %entry ], [ %indvar.next, %bb ]
+; CHECK-NEXT :   %tmp5 = icmp eq i8 %mode.0, 1
+; CHECK-NEXT :   %indvar.next = add i8 %mode.0, 1
+; CHECK-NEXT :   br i1 %tmp5, label %bb5, label %bb
+; CHECK-NEXT :
+; CHECK-NEXT : bb5:                                              ; preds = %bb
+; CHECK-NEXT :   tail call void @raise_exception() #0
+; CHECK-NEXT :   unreachable
+; CHECK-NEXT : }
+; CHECK-NEXT :
+; CHECK-NEXT : ; Function Attrs: noreturn
+; CHECK-NEXT : declare void @raise_exception() #0
+; CHECK-NEXT :
+; CHECK-NEXT : attributes #0 = { noreturn }
+
+define i8 @f() {
+entry:
+  br label %bb
+
+bb:                                               ; preds = %bb4, %entry
+  %mode.0 = phi i8 [ 0, %entry ], [ %indvar.next, %bb4 ]
+  %tmp5 = icmp eq i8 %mode.0, 1
+  br i1 %tmp5, label %bb5, label %bb4
+
+bb4:                                              ; preds = %bb2
+  %indvar.next = add i8 %mode.0, 1
+  br label %bb
+
+bb5:                                              ; preds = %bb2
+  tail call void @raise_exception() #0
+  unreachable
+}
+
+; Function Attrs: noreturn
+declare void @raise_exception() #0
+
+attributes #0 = { noreturn }