[PATCH] D29156: [LoopUnroll] Properly update loopinfo for runtime unrolling by 2

[Michael Kuperstein via Phabricator via llvm-commits]

mkuper created this revision.

Even when we don't actually create a remainder loop (that is, when we unroll by 2), we may have nested loops that we need to create.
This is complicated by the fact the remainder may either live in an outer loop or in the top-level, which means we may create new top-level loops.

I'm not too happy with this patch, better suggestions are welcome.


https://reviews.llvm.org/D29156

Files:
  lib/Transforms/Utils/LoopUnroll.cpp
  lib/Transforms/Utils/LoopUnrollRuntime.cpp
  test/Transforms/LoopUnroll/runtime-li.ll


Index: test/Transforms/LoopUnroll/runtime-li.ll
===================================================================
--- test/Transforms/LoopUnroll/runtime-li.ll
+++ test/Transforms/LoopUnroll/runtime-li.ll
@@ -0,0 +1,34 @@
+; RUN: opt -S -loop-unroll -unroll-runtime -unroll-count=2 -verify-loop-info -pass-remarks=loop-unroll < %s 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: remark: {{.*}}: unrolled loop by a factor of 2 with run-time trip count
+; CHECK: @widget
+; CHECK: ret void
+define void @widget(double* %arg, double* %arg1) local_unnamed_addr {
+bb:
+  br label %bb2
+
+bb2:                                              ; preds = %bb7, %bb
+  %tmp = phi double* [ %tmp8, %bb7 ], [ undef, %bb ]
+  br label %bb3
+
+bb3:                                              ; preds = %bb4, %bb2
+  br i1 undef, label %bb4, label %bb7
+
+bb4:                                              ; preds = %bb3
+  %tmp5 = load i64, i64* undef, align 8
+  store i64 %tmp5, i64* undef, align 8
+  %tmp6 = icmp eq double* undef, %arg
+  br label %bb3
+
+bb7:                                              ; preds = %bb3
+  store double undef, double* undef, align 8
+  %tmp8 = getelementptr inbounds double, double* %tmp, i64 1
+  %tmp9 = icmp eq double* %tmp8, %arg1
+  br i1 %tmp9, label %bb10, label %bb2
+
+bb10:                                             ; preds = %bb7
+  ret void
+}
Index: lib/Transforms/Utils/LoopUnrollRuntime.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -311,17 +311,21 @@
   }
 
   NewLoopsMap NewLoops;
-  NewLoops[L] = NewLoop;
+  if (NewLoop)
+    NewLoops[L] = NewLoop;
+  else if (ParentLoop)
+    NewLoops[L] = ParentLoop;
   // For each block in the original loop, create a new copy,
   // and update the value map with the newly created values.
   for (LoopBlocksDFS::RPOIterator BB = BlockBegin; BB != BlockEnd; ++BB) {
     BasicBlock *NewBB = CloneBasicBlock(*BB, VMap, "." + suffix, F);
     NewBlocks.push_back(NewBB);
-
-    if (NewLoop) {
-      addClonedBlockToLoopInfo(*BB, NewBB, LI, NewLoops);
-    } else if (ParentLoop)
-      ParentLoop->addBasicBlockToLoop(NewBB, *LI);
+   
+    // If we're unrolling the outernmost loop, there's no remainder loop,
+    // and this block isn't in a nested loop, then the new block is not
+    // in any loop. Otherwise, add it to loopinfo.
+    if (CreateRemainderLoop || LI->getLoopFor(*BB) != L || ParentLoop)
+        addClonedBlockToLoopInfo(*BB, NewBB, LI, NewLoops);
 
     VMap[*BB] = NewBB;
     if (Header == *BB) {
Index: lib/Transforms/Utils/LoopUnroll.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnroll.cpp
+++ lib/Transforms/Utils/LoopUnroll.cpp
@@ -199,11 +199,15 @@
     assert(OriginalBB == OldLoop->getHeader() &&
            "Header should be first in RPO");
 
+    NewLoop = new Loop();
     Loop *NewLoopParent = NewLoops.lookup(OldLoop->getParentLoop());
-    assert(NewLoopParent &&
-           "Expected parent loop before sub-loop in RPO");
-    NewLoop = new Loop;
-    NewLoopParent->addChildLoop(NewLoop);
+
+    if (NewLoopParent) {
+      NewLoopParent->addChildLoop(NewLoop);
+    } else {
+      LI->addTopLevelLoop(NewLoop);
+    }
+
     NewLoop->addBasicBlockToLoop(ClonedBB, *LI);
     return OldLoop;
   } else {


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