[PATCH] D53876: Preserve loop metadata when splitting exit blocks

[Chang Lin via Phabricator via llvm-commits]

clin1 updated this revision to Diff 174466.
clin1 added a comment.

Remove duplicate blocks from the list of exit predecessors. This happens when the predecessor inst is a switch with duplicate targets. Avoids block double-processing and maintains the metadata consistency assertion.


Repository:
  rL LLVM

https://reviews.llvm.org/D53876

Files:
  lib/Transforms/Utils/LoopUtils.cpp
  test/Transforms/LoopSimplify/preserve-llvm-loop-metadata2.ll


Index: test/Transforms/LoopSimplify/preserve-llvm-loop-metadata2.ll
===================================================================
--- test/Transforms/LoopSimplify/preserve-llvm-loop-metadata2.ll
+++ test/Transforms/LoopSimplify/preserve-llvm-loop-metadata2.ll
@@ -10,7 +10,10 @@
 
 ; CHECK: outer.header.loopexit:
 ; CHECK-NEXT: llvm.loop [[UJAMTAG:.*]]
-; CHECK-NOT: br i1 {{.*}}, label {{.*}}, label %outer.header.loopexit, !llvm.loop
+; CHECK: switch {{.*}}, label %inner.body [
+; CHECK-NEXT: i64 0, label %outer.header.loopexit
+; CHECK-NEXT: i64 1, label %outer.header.loopexit
+; CHECK-NOT: ], !llvm.loop
 ; CHECK: br label %inner.header, !llvm.loop [[UNROLLTAG:.*]]
 
 ; CHECK: distinct !{[[UJAMTAG]], [[UJAM:.*]]}
@@ -23,8 +26,8 @@
 entry:
   br label %outer.header
 
-outer.header:                                         ; preds = %inner.header, %entry
-  %ii.0 = phi i64 [ 2, %entry ], [ %add, %inner.header ]
+outer.header:                                         ; preds = %entry, %inner.header, %inner.header
+  %ii.0 = phi i64 [ 0, %entry ], [ %add, %inner.header ], [ %add, %inner.header ]
   %cmp = icmp ult i64 %ii.0, 64
   br i1 %cmp, label %inner.header, label %outer.header.cleanup
 
@@ -34,8 +37,12 @@
 inner.header:                                        ; preds = %outer.header, %inner.body
   %j.0 = phi i64 [ %add10, %inner.body ], [ %ii.0, %outer.header ]
   %add = add nuw nsw i64 %ii.0, 16
-  %cmp2 = icmp ult i64 %j.0, %add
-  br i1 %cmp2, label %inner.body, label %outer.header, !llvm.loop !2
+  %sub = sub i64 %add, %j.0
+; corner case: latch to outer loop is switch with duplicate edges
+  switch i64 %sub, label %inner.body [
+    i64 0, label %outer.header
+    i64 1, label %outer.header
+  ], !llvm.loop !2
 
 inner.body:                                        ; preds = %inner.header
   %add10 = add nuw nsw i64 %j.0, 1
Index: lib/Transforms/Utils/LoopUtils.cpp
===================================================================
--- lib/Transforms/Utils/LoopUtils.cpp
+++ lib/Transforms/Utils/LoopUtils.cpp
@@ -68,6 +68,11 @@
         IsDedicatedExit = false;
       }
 
+    // Remove duplicate pred blocks (ex: switch pred with duplicate edges)
+    auto LastPred =
+        std::unique(InLoopPredecessors.begin(), InLoopPredecessors.end());
+    InLoopPredecessors.erase(LastPred, InLoopPredecessors.end());
+
     assert(!InLoopPredecessors.empty() && "Must have *some* loop predecessor!");
 
     // Nothing to do if this is already a dedicated exit.


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