[PATCH] D98263: [LoopInterchange] fix tightlyNested() in LoopInterchange legality

[Congzhe Cao via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG829c1b644390: [LoopInterchange] fix tightlyNested() in LoopInterchange legality (authored by congzhe).

Changed prior to commit:
  https://reviews.llvm.org/D98263?vs=332847&id=333094#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D98263/new/

https://reviews.llvm.org/D98263

Files:
  llvm/lib/Transforms/Scalar/LoopInterchange.cpp
  llvm/test/Transforms/LoopInterchange/not-interchanged-tightly-nested.ll


Index: llvm/test/Transforms/LoopInterchange/not-interchanged-tightly-nested.ll
===================================================================
--- llvm/test/Transforms/LoopInterchange/not-interchanged-tightly-nested.ll
+++ llvm/test/Transforms/LoopInterchange/not-interchanged-tightly-nested.ll
@@ -103,3 +103,41 @@
 for.end12:
   ret void
 }
+
+;; The following Loop is not considered tightly nested and is not interchanged.
+;; The outer loop header does not branch to the inner loop preheader, or the
+;; inner loop header, or the outer loop latch.
+; CHECK: Not interchanging loops. Cannot prove legality.
+define void @interchange_07(i32 %k, i32 %N, i32 %ny) {
+entry:
+  br label %for1.header
+
+for1.header:
+  %j23 = phi i32 [ 0, %entry ], [ %j.next24, %for1.inc10 ]
+  %cmp21 = icmp slt i32 0, %ny
+  br label %singleSucc
+
+singleSucc:
+  br i1 %cmp21, label %preheader.j, label %for1.inc10
+
+preheader.j:
+  br label %for2
+
+for2:
+  %j = phi i32 [ %j.next, %for2 ], [ 0, %preheader.j ]
+  %arrayidx5 = getelementptr inbounds [100 x [100 x i32]], [100 x [100 x i32]]* @A, i32 0, i32 %j, i32 %j23
+  %lv = load i32, i32* %arrayidx5
+  %add = add nsw i32 %lv, %k
+  store i32 %add, i32* %arrayidx5
+  %j.next = add nuw nsw i32 %j, 1
+  %exitcond = icmp eq i32 %j, 99
+  br i1 %exitcond, label %for1.inc10, label %for2
+
+for1.inc10:
+  %j.next24 = add nuw nsw i32 %j23, 1
+  %exitcond26 = icmp eq i32 %j23, 99
+  br i1 %exitcond26, label %for.end12, label %for1.header
+
+for.end12:
+  ret void
+}
Index: llvm/lib/Transforms/Scalar/LoopInterchange.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -19,6 +19,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Analysis/DependenceAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopNestAnalysis.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/ScalarEvolution.h"
@@ -617,6 +618,22 @@
       containsUnsafeInstructions(InnerLoopPreHeader))
     return false;
 
+  BasicBlock *InnerLoopExit = InnerLoop->getExitBlock();
+  // Ensure the inner loop exit block flows to the outer loop latch possibly
+  // through empty blocks.
+  const BasicBlock &SuccInner =
+      LoopNest::skipEmptyBlockUntil(InnerLoopExit, OuterLoopLatch);
+  if (&SuccInner != OuterLoopLatch) {
+    LLVM_DEBUG(dbgs() << "Inner loop exit block " << *InnerLoopExit
+                      << " does not lead to the outer loop latch.\n";);
+    return false;
+  }
+  // The inner loop exit block does flow to the outer loop latch and not some
+  // other BBs, now make sure it contains safe instructions, since it will be
+  // moved into the (new) inner loop after interchange.
+  if (containsUnsafeInstructions(InnerLoopExit))
+    return false;
+
   LLVM_DEBUG(dbgs() << "Loops are perfectly nested\n");
   // We have a perfect loop nest.
   return true;


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