[LoopRotate] add ability to repeat loop rotation until non-deoptimizing exit is found

In case of loops with multiple exit where all-but-one exit are deoptimizing
it might happen that the first rotation will end up with latch having a deoptimizing
exit. This makes the loop unsuitable for trip-count analysis (say, getLoopEstimatedTripCount)
as well as for loop transformations that know how to handle multple deoptimizing exits.

It pretty much means that canonical form in multple-deoptimizing-exits case should be
with non-deoptimizing exit at latch.
Teach loop-rotation to reach this canonical form by repeating rotation.

-loop-rotate-multi option introduced to control this behavior, currently disabled by default.

Reviewers: skatkov, asbirlea, reames, fhahn
Reviewed By: skatkov

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73058

llvm/lib/Transforms/Utils/LoopRotationUtils.cpp

@@ -46,6 +46,11 @@ using namespace llvm;
 
 STATISTIC(NumRotated, "Number of loops rotated");
 
+static cl::opt<bool>
+    MultiRotate("loop-rotate-multi", cl::init(false), cl::Hidden,
+                cl::desc("Allow loop rotation multiple times in order to reach "
+                         "a better latch exit"));
+
 namespace {
 /// A simple loop rotation transformation.
 class LoopRotate {
@@ -177,14 +182,16 @@ static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
   }
 }
 
-// Look for a phi which is only used outside the loop (via a LCSSA phi)
-// in the exit from the header. This means that rotating the loop can
-// remove the phi.
-static bool shouldRotateLoopExitingLatch(Loop *L) {
+// Assuming both header and latch are exiting, look for a phi which is only
+// used outside the loop (via a LCSSA phi) in the exit from the header.
+// This means that rotating the loop can remove the phi.
+static bool profitableToRotateLoopExitingLatch(Loop *L) {
   BasicBlock *Header = L->getHeader();
-  BasicBlock *HeaderExit = Header->getTerminator()->getSuccessor(0);
+  BranchInst *BI = dyn_cast<BranchInst>(Header->getTerminator());
+  assert(BI && BI->isConditional() && "need header with conditional exit");
+  BasicBlock *HeaderExit = BI->getSuccessor(0);
   if (L->contains(HeaderExit))
-    HeaderExit = Header->getTerminator()->getSuccessor(1);
+    HeaderExit = BI->getSuccessor(1);
 
   for (auto &Phi : Header->phis()) {
     // Look for uses of this phi in the loop/via exits other than the header.
@@ -194,7 +201,50 @@ static bool shouldRotateLoopExitingLatch(Loop *L) {
       continue;
     return true;
   }
+  return false;
+}
 
+// Check that latch exit is deoptimizing (which means - very unlikely to happen)
+// and there is another exit from the loop which is non-deoptimizing.
+// If we rotate latch to that exit our loop has a better chance of being fully
+// canonical.
+//
+// It can give false positives in some rare cases.
+static bool canRotateDeoptimizingLatchExit(Loop *L) {
+  BasicBlock *Latch = L->getLoopLatch();
+  assert(Latch && "need latch");
+  BranchInst *BI = dyn_cast<BranchInst>(Latch->getTerminator());
+  // Need normal exiting latch.
+  if (!BI || !BI->isConditional())
+    return false;
+
+  BasicBlock *Exit = BI->getSuccessor(1);
+  if (L->contains(Exit))
+    Exit = BI->getSuccessor(0);
+
+  // Latch exit is non-deoptimizing, no need to rotate.
+  if (!Exit->getPostdominatingDeoptimizeCall())
+    return false;
+
+  SmallVector<BasicBlock *, 4> Exits;
+  L->getUniqueExitBlocks(Exits);
+  if (!Exits.empty()) {
+    // There is at least one non-deoptimizing exit.
+    //
+    // Note, that BasicBlock::getPostdominatingDeoptimizeCall is not exact,
+    // as it can conservatively return false for deoptimizing exits with
+    // complex enough control flow down to deoptimize call.
+    //
+    // That means here we can report success for a case where
+    // all exits are deoptimizing but one of them has complex enough
+    // control flow (e.g. with loops).
+    //
+    // That should be a very rare case and false positives for this function
+    // have compile-time effect only.
+    return any_of(Exits, [](const BasicBlock *BB) {
+      return !BB->getPostdominatingDeoptimizeCall();
+    });
+  }
   return false;
 }
 
@@ -208,34 +258,40 @@ static bool shouldRotateLoopExitingLatch(Loop *L) {
 /// rotation. LoopRotate should be repeatable and converge to a canonical
 /// form. This property is satisfied because simplifying the loop latch can only
 /// happen once across multiple invocations of the LoopRotate pass.
+///
+/// If -loop-rotate-multi is enabled we can do multiple rotations in one go
+/// so to reach a suitable (non-deoptimizing) exit.
 bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
   // If the loop has only one block then there is not much to rotate.
   if (L->getBlocks().size() == 1)
     return false;
 
+  bool Rotated = false;
+  do {
     BasicBlock *OrigHeader = L->getHeader();
     BasicBlock *OrigLatch = L->getLoopLatch();
 
     BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
     if (!BI || BI->isUnconditional())
-    return false;
+      return Rotated;
 
     // If the loop header is not one of the loop exiting blocks then
     // either this loop is already rotated or it is not
     // suitable for loop rotation transformations.
     if (!L->isLoopExiting(OrigHeader))
-    return false;
+      return Rotated;
 
     // If the loop latch already contains a branch that leaves the loop then the
     // loop is already rotated.
     if (!OrigLatch)
-    return false;
+      return Rotated;
 
     // Rotate if either the loop latch does *not* exit the loop, or if the loop
     // latch was just simplified. Or if we think it will be profitable.
     if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch && IsUtilMode == false &&
-      !shouldRotateLoopExitingLatch(L))
-    return false;
+        !profitableToRotateLoopExitingLatch(L) &&
+        !canRotateDeoptimizingLatchExit(L))
+      return Rotated;
 
     // Check size of original header and reject loop if it is very big or we can't
     // duplicate blocks inside it.
@@ -250,16 +306,16 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
                    dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
                    << " instructions: ";
                    L->dump());
-      return false;
+        return Rotated;
       }
       if (Metrics.convergent) {
         LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
                    "instructions: ";
                    L->dump());
-      return false;
+        return Rotated;
       }
       if (Metrics.NumInsts > MaxHeaderSize)
-      return false;
+        return Rotated;
     }
 
     // Now, this loop is suitable for rotation.
@@ -268,7 +324,7 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
     // If the loop could not be converted to canonical form, it must have an
     // indirectbr in it, just give up.
     if (!OrigPreheader || !L->hasDedicatedExits())
-    return false;
+      return Rotated;
 
     // Anything ScalarEvolution may know about this loop or the PHI nodes
     // in its header will soon be invalidated. We should also invalidate
@@ -521,6 +577,17 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
     LLVM_DEBUG(dbgs() << "LoopRotation: into "; L->dump());
 
     ++NumRotated;
+
+    Rotated = true;
+    SimplifiedLatch = false;
+
+    // Check that new latch is a deoptimizing exit and then repeat rotation if possible.
+    // Deoptimizing latch exit is not a generally typical case, so we just loop over.
+    // TODO: if it becomes a performance bottleneck extend rotation algorithm
+    // to handle multiple rotations in one go.
+  } while (MultiRotate && canRotateDeoptimizingLatchExit(L));
+
+
   return true;
 }
 

llvm/test/Transforms/LoopRotate/multiple-deopt-exits.ll

@@ -0,0 +1,165 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S < %s -loop-rotate -loop-rotate-multi=true | FileCheck %s
+; RUN: opt -S < %s -passes='loop(rotate)' -loop-rotate-multi=true | FileCheck %s
+
+; Test loop rotation with multiple exits, some of them - deoptimizing.
+; We should end up with a latch which exit is non-deoptimizing, so we should rotate
+; more than once.
+
+declare i32 @llvm.experimental.deoptimize.i32(...)
+
+define i32 @test_cond_with_one_deopt_exit(i32 * nonnull %a, i64 %x) {
+; Rotation done twice.
+; Latch should be at the 2nd condition (for.cond2), exiting to %return.
+;
+; CHECK-LABEL: @test_cond_with_one_deopt_exit(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[VAL_A_IDX3:%.*]] = load i32, i32* %a, align 4
+; CHECK-NEXT:    [[ZERO_CHECK4:%.*]] = icmp eq i32 [[VAL_A_IDX3]], 0
+; CHECK-NEXT:    br i1 [[ZERO_CHECK4]], label %deopt.exit, label %for.cond2.lr.ph
+; CHECK:       for.cond2.lr.ph:
+; CHECK-NEXT:    [[FOR_CHECK8:%.*]] = icmp ult i64 0, %x
+; CHECK-NEXT:    br i1 [[FOR_CHECK8]], label %for.body.lr.ph, label %return
+; CHECK:       for.body.lr.ph:
+; CHECK-NEXT:    br label %for.body
+; CHECK:       for.cond2:
+; CHECK:         [[FOR_CHECK:%.*]] = icmp ult i64 {{%.*}}, %x
+; CHECK-NEXT:    br i1 [[FOR_CHECK]], label %for.body, label %for.cond2.return_crit_edge
+; CHECK:       for.body:
+; CHECK:         br label %for.tail
+; CHECK:       for.tail:
+; CHECK:         [[VAL_A_IDX:%.*]] = load i32, i32*
+; CHECK-NEXT:    [[ZERO_CHECK:%.*]] = icmp eq i32 [[VAL_A_IDX]], 0
+; CHECK-NEXT:    br i1 [[ZERO_CHECK]], label %for.cond1.deopt.exit_crit_edge, label %for.cond2
+; CHECK:       for.cond2.return_crit_edge:
+; CHECK-NEXT:    {{%.*}} = phi i32
+; CHECK-NEXT:    br label %return
+; CHECK:       return:
+; CHECK-NEXT:    [[SUM_LCSSA2:%.*]] = phi i32
+; CHECK-NEXT:    ret i32 [[SUM_LCSSA2]]
+; CHECK:       for.cond1.deopt.exit_crit_edge:
+; CHECK-NEXT:    {{%.*}} = phi i32
+; CHECK-NEXT:    br label %deopt.exit
+; CHECK:       deopt.exit:
+; CHECK:         [[DEOPT_VAL:%.*]] = call i32 (...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 {{%.*}}) ]
+; CHECK-NEXT:    ret i32 [[DEOPT_VAL]]
+;
+entry:
+  br label %for.cond1
+
+for.cond1:
+  %idx = phi i64 [ 0, %entry ], [ %idx.next, %for.tail ]
+  %sum = phi i32 [ 0, %entry ], [ %sum.next, %for.tail ]
+  %a.idx = getelementptr inbounds i32, i32 *%a, i64 %idx
+  %val.a.idx = load i32, i32* %a.idx, align 4
+  %zero.check = icmp eq i32 %val.a.idx, 0
+  br i1 %zero.check, label %deopt.exit, label %for.cond2
+
+for.cond2:
+  %for.check = icmp ult i64 %idx, %x
+  br i1 %for.check, label %for.body, label %return
+
+for.body:
+  br label %for.tail
+
+for.tail:
+  %sum.next = add i32 %sum, %val.a.idx
+  %idx.next = add nuw nsw i64 %idx, 1
+  br label %for.cond1
+
+return:
+  ret i32 %sum
+
+deopt.exit:
+  %deopt.val = call i32(...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 %val.a.idx) ]
+  ret i32 %deopt.val
+}
+
+define i32 @test_cond_with_two_deopt_exits(i32 ** nonnull %a, i64 %x) {
+; Rotation done three times.
+; Latch should be at the 3rd condition (for.cond3), exiting to %return.
+;
+; CHECK-LABEL: @test_cond_with_two_deopt_exits(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[A_IDX_DEREF4:%.*]] = load i32*, i32** %a
+; CHECK-NEXT:    [[NULL_CHECK5:%.*]] = icmp eq i32* [[A_IDX_DEREF4]], null
+; CHECK-NEXT:    br i1 [[NULL_CHECK5]], label %deopt.exit1, label %for.cond2.lr.ph
+; CHECK:       for.cond2.lr.ph:
+; CHECK-NEXT:    [[VAL_A_IDX9:%.*]] = load i32, i32* [[A_IDX_DEREF4]], align 4
+; CHECK-NEXT:    [[ZERO_CHECK10:%.*]] = icmp eq i32 [[VAL_A_IDX9]], 0
+; CHECK-NEXT:    br i1 [[ZERO_CHECK10]], label %deopt.exit2, label %for.cond3.lr.ph
+; CHECK:       for.cond3.lr.ph:
+; CHECK-NEXT:    [[FOR_CHECK14:%.*]] = icmp ult i64 0, %x
+; CHECK-NEXT:    br i1 [[FOR_CHECK14]], label %for.body.lr.ph, label %return
+; CHECK:       for.body.lr.ph:
+; CHECK-NEXT:    br label %for.body
+; CHECK:       for.cond2:
+; CHECK:         [[VAL_A_IDX:%.*]] = load i32, i32*
+; CHECK-NEXT:    [[ZERO_CHECK:%.*]] = icmp eq i32 [[VAL_A_IDX]], 0
+; CHECK-NEXT:    br i1 [[ZERO_CHECK]], label %for.cond2.deopt.exit2_crit_edge, label %for.cond3
+; CHECK:       for.cond3:
+; CHECK:         [[FOR_CHECK:%.*]] = icmp ult i64 {{%.*}}, %x
+; CHECK-NEXT:    br i1 [[FOR_CHECK]], label %for.body, label %for.cond3.return_crit_edge
+; CHECK:       for.body:
+; CHECK:         br label %for.tail
+; CHECK:       for.tail:
+; CHECK:         [[IDX_NEXT:%.*]] = add nuw nsw i64 {{%.*}}, 1
+; CHECK:         [[NULL_CHECK:%.*]] = icmp eq i32* {{%.*}}, null
+; CHECK-NEXT:    br i1 [[NULL_CHECK]], label %for.cond1.deopt.exit1_crit_edge, label %for.cond2
+; CHECK:       for.cond3.return_crit_edge:
+; CHECK-NEXT:    [[SPLIT18:%.*]] = phi i32
+; CHECK-NEXT:    br label %return
+; CHECK:       return:
+; CHECK-NEXT:    [[SUM_LCSSA2:%.*]] = phi i32
+; CHECK-NEXT:    ret i32 [[SUM_LCSSA2]]
+; CHECK:       for.cond1.deopt.exit1_crit_edge:
+; CHECK-NEXT:    br label %deopt.exit1
+; CHECK:       deopt.exit1:
+; CHECK-NEXT:    [[DEOPT_VAL1:%.*]] = call i32 (...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 0) ]
+; CHECK-NEXT:    ret i32 [[DEOPT_VAL1]]
+; CHECK:       for.cond2.deopt.exit2_crit_edge:
+; CHECK-NEXT:    [[SPLIT:%.*]] = phi i32
+; CHECK-NEXT:    br label %deopt.exit2
+; CHECK:       deopt.exit2:
+; CHECK-NEXT:    [[VAL_A_IDX_LCSSA:%.*]] = phi i32
+; CHECK-NEXT:    [[DEOPT_VAL2:%.*]] = call i32 (...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 [[VAL_A_IDX_LCSSA]]) ]
+; CHECK-NEXT:    ret i32 [[DEOPT_VAL2]]
+;
+entry:
+  br label %for.cond1
+
+for.cond1:
+  %idx = phi i64 [ 0, %entry ], [ %idx.next, %for.tail ]
+  %sum = phi i32 [ 0, %entry ], [ %sum.next, %for.tail ]
+  %a.idx = getelementptr inbounds i32*, i32 **%a, i64 %idx
+  %a.idx.deref = load i32*, i32** %a.idx
+  %null.check = icmp eq i32* %a.idx.deref, null
+  br i1 %null.check, label %deopt.exit1, label %for.cond2
+
+for.cond2:
+  %val.a.idx = load i32, i32* %a.idx.deref, align 4
+  %zero.check = icmp eq i32 %val.a.idx, 0
+  br i1 %zero.check, label %deopt.exit2, label %for.cond3
+
+for.cond3:
+  %for.check = icmp ult i64 %idx, %x
+  br i1 %for.check, label %for.body, label %return
+
+for.body:
+  br label %for.tail
+
+for.tail:
+  %sum.next = add i32 %sum, %val.a.idx
+  %idx.next = add nuw nsw i64 %idx, 1
+  br label %for.cond1
+
+return:
+  ret i32 %sum
+
+deopt.exit1:
+  %deopt.val1 = call i32(...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 0) ]
+  ret i32 %deopt.val1
+deopt.exit2:
+  %deopt.val2 = call i32(...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 %val.a.idx) ]
+  ret i32 %deopt.val2
+}

llvm/unittests/Transforms/Utils/CMakeLists.txt

@@ -15,6 +15,7 @@ add_llvm_unittest(UtilsTests
   FunctionComparatorTest.cpp
   IntegerDivisionTest.cpp
   LocalTest.cpp
+  LoopRotationUtilsTest.cpp
   LoopUtilsTest.cpp
   SizeOptsTest.cpp
   SSAUpdaterBulkTest.cpp

llvm/unittests/Transforms/Utils/LoopRotationUtilsTest.cpp

@@ -0,0 +1,166 @@
+//===- LoopRotationUtilsTest.cpp - Unit tests for LoopRotation utility ----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/LoopRotationUtils.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+static std::unique_ptr<Module> parseIR(LLVMContext &C, const char *IR) {
+  SMDiagnostic Err;
+  std::unique_ptr<Module> Mod = parseAssemblyString(IR, Err, C);
+  if (!Mod)
+    Err.print("LoopRotationUtilsTest", errs());
+  return Mod;
+}
+
+/// This test contains multi-deopt-exits pattern that might allow loop rotation
+/// to trigger multiple times if multiple rotations are enabled.
+/// At least one rotation should be performed, no matter what loop rotation settings are.
+TEST(LoopRotate, MultiDeoptExit) {
+  LLVMContext C;
+
+  std::unique_ptr<Module> M = parseIR(
+    C,
+    R"(
+declare i32 @llvm.experimental.deoptimize.i32(...)
+
+define i32 @test(i32 * nonnull %a, i64 %x) {
+entry:
+  br label %for.cond1
+
+for.cond1:
+  %idx = phi i64 [ 0, %entry ], [ %idx.next, %for.tail ]
+  %sum = phi i32 [ 0, %entry ], [ %sum.next, %for.tail ]
+  %a.idx = getelementptr inbounds i32, i32 *%a, i64 %idx
+  %val.a.idx = load i32, i32* %a.idx, align 4
+  %zero.check = icmp eq i32 %val.a.idx, 0
+  br i1 %zero.check, label %deopt.exit, label %for.cond2
+
+for.cond2:
+  %for.check = icmp ult i64 %idx, %x
+  br i1 %for.check, label %for.body, label %return
+
+for.body:
+  br label %for.tail
+
+for.tail:
+  %sum.next = add i32 %sum, %val.a.idx
+  %idx.next = add nuw nsw i64 %idx, 1
+  br label %for.cond1
+
+return:
+  ret i32 %sum
+
+deopt.exit:
+  %deopt.val = call i32(...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 %val.a.idx) ]
+  ret i32 %deopt.val
+})"
+    );
+
+  auto *F = M->getFunction("test");
+  DominatorTree DT(*F);
+  LoopInfo LI(DT);
+  AssumptionCache AC(*F);
+  TargetTransformInfo TTI(M->getDataLayout());
+  TargetLibraryInfoImpl TLII;
+  TargetLibraryInfo TLI(TLII);
+  ScalarEvolution SE(*F, TLI, AC, DT, LI);
+  SimplifyQuery SQ(M->getDataLayout());
+
+  Loop *L = *LI.begin();
+
+  bool ret = LoopRotation(L, &LI, &TTI,
+                          &AC, &DT,
+                          &SE, nullptr,
+                          SQ, true, -1, false);
+  EXPECT_TRUE(ret);
+}
+
+/// Checking a special case of multi-deopt exit loop that can not perform
+/// required amount of rotations due to the desired header containing
+/// non-duplicatable code.
+/// Similar to MultiDeoptExit test this one should do at least one rotation and
+/// pass no matter what loop rotation settings are.
+TEST(LoopRotate, MultiDeoptExit_Nondup) {
+  LLVMContext C;
+
+  std::unique_ptr<Module> M = parseIR(
+    C,
+    R"(
+; Rotation should be done once, attempted twice.
+; Second time fails due to non-duplicatable header.
+
+declare i32 @llvm.experimental.deoptimize.i32(...)
+
+declare void @nondup()
+
+define i32 @test_nondup(i32 * nonnull %a, i64 %x) {
+entry:
+  br label %for.cond1
+
+for.cond1:
+  %idx = phi i64 [ 0, %entry ], [ %idx.next, %for.tail ]
+  %sum = phi i32 [ 0, %entry ], [ %sum.next, %for.tail ]
+  %a.idx = getelementptr inbounds i32, i32 *%a, i64 %idx
+  %val.a.idx = load i32, i32* %a.idx, align 4
+  %zero.check = icmp eq i32 %val.a.idx, 0
+  br i1 %zero.check, label %deopt.exit, label %for.cond2
+
+for.cond2:
+  call void @nondup() noduplicate
+  %for.check = icmp ult i64 %idx, %x
+  br i1 %for.check, label %for.body, label %return
+
+for.body:
+  br label %for.tail
+
+for.tail:
+  %sum.next = add i32 %sum, %val.a.idx
+  %idx.next = add nuw nsw i64 %idx, 1
+  br label %for.cond1
+
+return:
+  ret i32 %sum
+
+deopt.exit:
+  %deopt.val = call i32(...) @llvm.experimental.deoptimize.i32() [ "deopt"(i32 %val.a.idx) ]
+  ret i32 %deopt.val
+})"
+    );
+
+  auto *F = M->getFunction("test_nondup");
+  DominatorTree DT(*F);
+  LoopInfo LI(DT);
+  AssumptionCache AC(*F);
+  TargetTransformInfo TTI(M->getDataLayout());
+  TargetLibraryInfoImpl TLII;
+  TargetLibraryInfo TLI(TLII);
+  ScalarEvolution SE(*F, TLI, AC, DT, LI);
+  SimplifyQuery SQ(M->getDataLayout());
+
+  Loop *L = *LI.begin();
+
+  bool ret = LoopRotation(L, &LI, &TTI,
+                          &AC, &DT,
+                          &SE, nullptr,
+                          SQ, true, -1, false);
+  /// LoopRotation should properly report "true" as we still perform the first rotation
+  /// so we do change the IR.
+  EXPECT_TRUE(ret);
+}