[LoopInterhcange] Handle movement of reduction phis appropriately during transformation (pr43326 && pr48212)

[congzhe]

Summary

This patch fixes pr43326(https://bugs.llvm.org/show_bug.cgi?id=43326) and pr48212(https://bugs.llvm.org/show_bug.cgi?id=48212). The test cases in pr43326 and pr48212 are added in lit tests.

Currently when we move reduction phis to the right place, this pass assumes the first phi in loop headers is an induction phi, skips the first phi and assume the rest of phis are candidate reduction phis to move. However, it may not always be the case.

This patch loops over all phis in loop headers and consider an phi as a candidate reduction phi to move only when it is indeed a reduction phi across outer and inner loop.

[congzhe]

ping @bmahjour @Whitney @fhahn

[Whitney]

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

6

This line can now be removed.

[congzhe]

Minor comments addressed

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

 //===- LoopInterchange.cpp - Loop interchange pass-------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This Pass handles loop interchange transform.
 // This pass interchanges loops to provide a more cache-friendly memory access
 // patterns.
 //
 //===----------------------------------------------------------------------===//
 
bool LoopInterchangeTransform::adjustLoopBranches() {
 
   moveLCSSAPhis(InnerLoopLatchSuccessor, InnerLoopHeader, InnerLoopLatch,
                 OuterLoopHeader, OuterLoopLatch, InnerLoop->getExitBlock(),
                 InnerLoop, LI);
   // For PHIs in the exit block of the outer loop, outer's latch has been
   // replaced by Inners'.
   OuterLoopLatchSuccessor->replacePhiUsesWith(OuterLoopLatch, InnerLoopLatch);
 
+  auto &OuterInnerReductions = LIL.getOuterInnerReductions();
   // Now update the reduction PHIs in the inner and outer loop headers.
   SmallVector<PHINode *, 4> InnerLoopPHIs, OuterLoopPHIs;
-  for (PHINode &PHI : drop_begin(InnerLoopHeader->phis()))
+  for (PHINode &PHI : InnerLoopHeader->phis()) {
+    if (OuterInnerReductions.find(&PHI) == OuterInnerReductions.end())
+      continue;
     InnerLoopPHIs.push_back(cast<PHINode>(&PHI));
-  for (PHINode &PHI : drop_begin(OuterLoopHeader->phis()))
+  }
+  for (PHINode &PHI : OuterLoopHeader->phis()) {
+    if (OuterInnerReductions.find(&PHI) == OuterInnerReductions.end())
+      continue;
     OuterLoopPHIs.push_back(cast<PHINode>(&PHI));
-
-  auto &OuterInnerReductions = LIL.getOuterInnerReductions();
-  (void)OuterInnerReductions;
+  }
 
   // Now move the remaining reduction PHIs from outer to inner loop header and
   // vice versa. The PHI nodes must be part of a reduction across the inner and
   // outer loop and all the remains to do is and updating the incoming blocks.
   for (PHINode *PHI : OuterLoopPHIs) {
     PHI->moveBefore(InnerLoopHeader->getFirstNonPHI());
     assert(OuterInnerReductions.count(PHI) && "Expected a reduction PHI node");
   }

llvm/test/Transforms/LoopInterchange/pr43326.ll

+; RUN: opt < %s -basic-aa -loop-interchange -pass-remarks-missed='loop-interchange' -pass-remarks-output=%t -S \
+; RUN:     -verify-dom-info -verify-loop-info -verify-loop-lcssa -stats 2>&1
+; RUN: FileCheck --input-file=%t --check-prefix=REMARKS %s
+
+@a = global i32 0
+@b = global i8 0
+@c = global i32 0
+@d = global i32 0
+@e = global [1 x [1 x i32]] zeroinitializer
+
+; REMARKS: --- !Passed
+; REMARKS-NEXT: Pass:            loop-interchange
+; REMARKS-NEXT: Name:            Interchanged
+; REMARKS-NEXT: Function:        pr43326
+
+define void @pr43326() {
+entry:
+  %0 = load i32, i32* @a
+  %tobool.not2 = icmp eq i32 %0, 0
+  br i1 %tobool.not2, label %for.end14, label %for.body.lr.ph
+
+for.body.lr.ph:                                   ; preds = %entry
+  %d.promoted = load i32, i32* @d
+  %a.promoted = load i32, i32* @a
+  br label %for.body
+
+for.body:                                         ; preds = %for.body.lr.ph, %for.inc12
+  %inc1312 = phi i32 [ %a.promoted, %for.body.lr.ph ], [ %inc13, %for.inc12 ]
+  %xor.lcssa.lcssa11 = phi i32 [ %d.promoted, %for.body.lr.ph ], [ %xor.lcssa.lcssa, %for.inc12 ]
+  br label %for.body3
+
+for.body3:                                        ; preds = %for.body, %for.inc10
+  %xor.lcssa9 = phi i32 [ %xor.lcssa.lcssa11, %for.body ], [ %xor.lcssa, %for.inc10 ]
+  %dec7 = phi i8 [ 0, %for.body ], [ %dec, %for.inc10 ]
+  %idxprom8 = sext i8 %dec7 to i64
+  br label %for.body7
+
+for.body7:                                        ; preds = %for.body3, %for.inc
+  %xor5 = phi i32 [ %xor.lcssa9, %for.body3 ], [ %xor, %for.inc ]
+  %inc4 = phi i32 [ 0, %for.body3 ], [ %inc, %for.inc ]
+  %idxprom = sext i32 %inc4 to i64
+  %arrayidx9 = getelementptr inbounds [1 x [1 x i32]], [1 x [1 x i32]]* @e, i64 0, i64 %idxprom, i64 %idxprom8
+  %1 = load i32, i32* %arrayidx9
+  %xor = xor i32 %xor5, %1
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body7
+  %inc = add nsw i32 %inc4, 1
+  %cmp5 = icmp slt i32 %inc, 1
+  br i1 %cmp5, label %for.body7, label %for.end
+
+for.end:                                          ; preds = %for.inc
+  %xor.lcssa = phi i32 [ %xor, %for.inc ]
+  %inc.lcssa = phi i32 [ %inc, %for.inc ]
+  br label %for.inc10
+
+for.inc10:                                        ; preds = %for.end
+  %dec = add i8 %dec7, -1
+  %cmp = icmp sgt i8 %dec, -1
+  br i1 %cmp, label %for.body3, label %for.end11
+
+for.end11:                                        ; preds = %for.inc10
+  %xor.lcssa.lcssa = phi i32 [ %xor.lcssa, %for.inc10 ]
+  %dec.lcssa = phi i8 [ %dec, %for.inc10 ]
+  %inc.lcssa.lcssa = phi i32 [ %inc.lcssa, %for.inc10 ]
+  br label %for.inc12
+
+for.inc12:                                        ; preds = %for.end11
+  %inc13 = add nsw i32 %inc1312, 1
+  %tobool.not = icmp eq i32 %inc13, 0
+  br i1 %tobool.not, label %for.cond.for.end14_crit_edge, label %for.body
+
+for.cond.for.end14_crit_edge:                     ; preds = %for.inc12
+  %inc13.lcssa = phi i32 [ %inc13, %for.inc12 ]
+  %inc.lcssa.lcssa.lcssa = phi i32 [ %inc.lcssa.lcssa, %for.inc12 ]
+  %xor.lcssa.lcssa.lcssa = phi i32 [ %xor.lcssa.lcssa, %for.inc12 ]
+  %dec.lcssa.lcssa = phi i8 [ %dec.lcssa, %for.inc12 ]
+  store i8 %dec.lcssa.lcssa, i8* @b
+  store i32 %xor.lcssa.lcssa.lcssa, i32* @d
+  store i32 %inc.lcssa.lcssa.lcssa, i32* @c
+  store i32 %inc13.lcssa, i32* @a
+  br label %for.end14
+
+for.end14:                                        ; preds = %for.cond.for.end14_crit_edge, %entry
+  ret void
+}

llvm/test/Transforms/LoopInterchange/pr48212.ll

+; RUN: opt < %s -basic-aa -loop-interchange -pass-remarks-missed='loop-interchange' -pass-remarks-output=%t -S \
+; RUN:     -verify-dom-info -verify-loop-info -verify-loop-lcssa 2>&1
+; RUN: FileCheck --input-file=%t --check-prefix=REMARKS %s
+
+; REMARKS: --- !Passed
+; REMARKS-NEXT: Pass:            loop-interchange
+; REMARKS-NEXT: Name:            Interchanged
+; REMARKS-NEXT: Function:        pr48212
+
+define void @pr48212([5 x i32]* %filter) #0 {
+entry:
+  br label %L1
+
+L1:                                               ; preds = %entry
+  br label %for.body
+
+for.body:                                         ; preds = %L1, %for.inc6
+  %temp.04 = phi i32 [ undef, %L1 ], [ %temp.1.lcssa, %for.inc6 ]
+  %k1.03 = phi i32 [ 0, %L1 ], [ %inc7, %for.inc6 ]
+  br label %L2
+
+L2:                                               ; preds = %for.body
+  br label %for.body3
+
+for.body3:                                        ; preds = %L2, %for.inc
+  %temp.12 = phi i32 [ %temp.04, %L2 ], [ %add, %for.inc ]
+  %k2.01 = phi i32 [ 0, %L2 ], [ %inc, %for.inc ]
+  %idxprom = sext i32 %k2.01 to i64
+  %arrayidx = getelementptr inbounds [5 x i32], [5 x i32]* %filter, i64 %idxprom
+  %idxprom4 = sext i32 %k1.03 to i64
+  %arrayidx5 = getelementptr inbounds [5 x i32], [5 x i32]* %arrayidx, i64 0, i64 %idxprom4
+  %0 = load i32, i32* %arrayidx5
+  %add = add nsw i32 %temp.12, %0
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body3
+  %inc = add nsw i32 %k2.01, 1
+  %cmp2 = icmp slt i32 %inc, 3
+  br i1 %cmp2, label %for.body3, label %for.end
+
+for.end:                                          ; preds = %for.inc
+  %temp.1.lcssa = phi i32 [ %add, %for.inc ]
+  br label %for.inc6
+
+for.inc6:                                         ; preds = %for.end
+  %inc7 = add nsw i32 %k1.03, 1
+  %cmp = icmp slt i32 %inc7, 5
+  br i1 %cmp, label %for.body, label %for.end8
+
+for.end8:                                         ; preds = %for.inc6
+  ret void
+}
+
+