[AArch64] Enable RT and partial unrolling for loops with reductions.

Update unrolling preferences for Apple Silicon CPUs to enable partial
unrolling and runtime unrolling for small loops with reductions.

This builds on top of unroller changes to introduce parallel reduction
phis, if possible: #149470.

Author: fhahn

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -25,6 +25,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/TargetParser/AArch64TargetParser.h"
 #include "llvm/Transforms/InstCombine/InstCombiner.h"
+#include "llvm/Transforms/Utils/UnrollLoop.h"
 #include "llvm/Transforms/Vectorize/LoopVectorizationLegality.h"
 #include <algorithm>
 #include <optional>
@@ -4787,6 +4788,19 @@ getAppleRuntimeUnrollPreferences(Loop *L, ScalarEvolution &SE,
   if (!L->getExitBlock())
     return;
 
+  // Check if the loop contains any reductions that could be parallelized when unrolling.
+  // If so, enable partial unrolling, if the trip count is know to be a multiple of 2.
+  bool HasParellelizableReductions =
+      L->getNumBlocks() == 1 &&
+      any_of(L->getHeader()->phis(), [&SE, L](PHINode &Phi) {
+        return canParallelizeReductionWhenUnrolling(Phi, L, &SE);
+      }) && isLoopSizeWithinBudget(L, TTI, 12, nullptr);
+  if (HasParellelizableReductions &&
+      SE.getSmallConstantTripMultiple(L, L->getExitingBlock()) % 2 == 0) {
+    UP.Partial = true;
+    UP.MaxCount = 4;
+  }
+
   const SCEV *BTC = SE.getSymbolicMaxBackedgeTakenCount(L);
   if (isa<SCEVConstant>(BTC) || isa<SCEVCouldNotCompute>(BTC) ||
       (SE.getSmallConstantMaxTripCount(L) > 0 &&
@@ -4802,6 +4816,11 @@ getAppleRuntimeUnrollPreferences(Loop *L, ScalarEvolution &SE,
   // Limit to loops with trip counts that are cheap to expand.
   UP.SCEVExpansionBudget = 1;
 
+  if (HasParellelizableReductions) {
+    UP.Runtime = true;
+    UP.DefaultUnrollRuntimeCount = 4;
+  }
+
   // Try to unroll small, single block loops, if they have load/store
   // dependencies, to expose more parallel memory access streams.
   BasicBlock *Header = L->getHeader();

llvm/test/Transforms/LoopUnroll/AArch64/apple-unrolling.ll

@@ -585,16 +585,34 @@ define i32 @test_add_reduction_unroll_partial(ptr %a, i64 noundef %n) {
 ; APPLE-NEXT:  [[ENTRY:.*]]:
 ; APPLE-NEXT:    br label %[[LOOP:.*]]
 ; APPLE:       [[LOOP]]:
-; APPLE-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT_3:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_1:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT_1:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_2:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT_2:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_3:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT_3:%.*]], %[[LOOP]] ]
 ; APPLE-NEXT:    [[RDX:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT:%.*]], %[[LOOP]] ]
 ; APPLE-NEXT:    [[GEP_A:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV]]
 ; APPLE-NEXT:    [[TMP0:%.*]] = load i32, ptr [[GEP_A]], align 2
-; APPLE-NEXT:    [[RDX_NEXT]] = add nuw nsw i32 [[RDX]], [[TMP0]]
-; APPLE-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
-; APPLE-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], 1024
-; APPLE-NEXT:    br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; APPLE-NEXT:    [[RDX_NEXT]] = add i32 [[RDX]], [[TMP0]]
+; APPLE-NEXT:    [[IV_NEXT:%.*]] = add nuw nsw i64 [[IV]], 1
+; APPLE-NEXT:    [[GEP_A_1:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT]]
+; APPLE-NEXT:    [[TMP1:%.*]] = load i32, ptr [[GEP_A_1]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_1]] = add i32 [[RDX_1]], [[TMP1]]
+; APPLE-NEXT:    [[IV_NEXT_1:%.*]] = add nuw nsw i64 [[IV]], 2
+; APPLE-NEXT:    [[GEP_A_2:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT_1]]
+; APPLE-NEXT:    [[TMP2:%.*]] = load i32, ptr [[GEP_A_2]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_2]] = add i32 [[RDX_2]], [[TMP2]]
+; APPLE-NEXT:    [[IV_NEXT_2:%.*]] = add nuw nsw i64 [[IV]], 3
+; APPLE-NEXT:    [[GEP_A_3:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT_2]]
+; APPLE-NEXT:    [[TMP3:%.*]] = load i32, ptr [[GEP_A_3]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_3]] = add i32 [[RDX_3]], [[TMP3]]
+; APPLE-NEXT:    [[IV_NEXT_3]] = add nuw nsw i64 [[IV]], 4
+; APPLE-NEXT:    [[EC_3:%.*]] = icmp eq i64 [[IV_NEXT_3]], 1024
+; APPLE-NEXT:    br i1 [[EC_3]], label %[[EXIT:.*]], label %[[LOOP]]
 ; APPLE:       [[EXIT]]:
-; APPLE-NEXT:    [[BIN_RDX2:%.*]] = phi i32 [ [[RDX_NEXT]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RES:%.*]] = phi i32 [ [[RDX_NEXT_3]], %[[LOOP]] ]
+; APPLE-NEXT:    [[BIN_RDX:%.*]] = add i32 [[RDX_NEXT_1]], [[RDX_NEXT]]
+; APPLE-NEXT:    [[BIN_RDX1:%.*]] = add i32 [[RDX_NEXT_2]], [[BIN_RDX]]
+; APPLE-NEXT:    [[BIN_RDX2:%.*]] = add i32 [[RDX_NEXT_3]], [[BIN_RDX1]]
 ; APPLE-NEXT:    ret i32 [[BIN_RDX2]]
 ;
 ; OTHER-LABEL: define i32 @test_add_reduction_unroll_partial(
@@ -731,21 +749,42 @@ define i32 @test_add_and_mul_reduction_unroll_partial(ptr %a, i64 noundef %n) {
 ; APPLE-NEXT:  [[ENTRY:.*]]:
 ; APPLE-NEXT:    br label %[[LOOP:.*]]
 ; APPLE:       [[LOOP]]:
-; APPLE-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
-; APPLE-NEXT:    [[RDX:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT:%.*]], %[[LOOP]] ]
-; APPLE-NEXT:    [[RDX_2:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_2_NEXT:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[IV:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT_3:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_1:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[BIN_RDX3:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_21:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT_2:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_3:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT_3:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RES_2:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_2:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_2_NEXT_3:%.*]], %[[LOOP]] ]
 ; APPLE-NEXT:    [[GEP_A:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV]]
 ; APPLE-NEXT:    [[TMP0:%.*]] = load i32, ptr [[GEP_A]], align 2
-; APPLE-NEXT:    [[RDX_NEXT]] = add nuw nsw i32 [[RDX]], [[TMP0]]
-; APPLE-NEXT:    [[RDX_2_NEXT]] = mul i32 [[RDX_2]], [[TMP0]]
-; APPLE-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
-; APPLE-NEXT:    [[EC:%.*]] = icmp eq i64 [[IV_NEXT]], 1024
-; APPLE-NEXT:    br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
+; APPLE-NEXT:    [[RES_2]] = add i32 [[RDX]], [[TMP0]]
+; APPLE-NEXT:    [[RDX_2_NEXT:%.*]] = mul i32 [[RDX_2]], [[TMP0]]
+; APPLE-NEXT:    [[IV_NEXT:%.*]] = add nuw nsw i64 [[IV]], 1
+; APPLE-NEXT:    [[GEP_A_1:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT]]
+; APPLE-NEXT:    [[TMP1:%.*]] = load i32, ptr [[GEP_A_1]], align 2
+; APPLE-NEXT:    [[BIN_RDX3]] = add i32 [[RDX_1]], [[TMP1]]
+; APPLE-NEXT:    [[RDX_2_NEXT_1:%.*]] = mul i32 [[RDX_2_NEXT]], [[TMP1]]
+; APPLE-NEXT:    [[IV_NEXT_1:%.*]] = add nuw nsw i64 [[IV]], 2
+; APPLE-NEXT:    [[GEP_A_2:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT_1]]
+; APPLE-NEXT:    [[TMP2:%.*]] = load i32, ptr [[GEP_A_2]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_2]] = add i32 [[RDX_21]], [[TMP2]]
+; APPLE-NEXT:    [[RDX_2_NEXT_2:%.*]] = mul i32 [[RDX_2_NEXT_1]], [[TMP2]]
+; APPLE-NEXT:    [[IV_NEXT_2:%.*]] = add nuw nsw i64 [[IV]], 3
+; APPLE-NEXT:    [[GEP_A_3:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT_2]]
+; APPLE-NEXT:    [[TMP3:%.*]] = load i32, ptr [[GEP_A_3]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_3]] = add i32 [[RDX_3]], [[TMP3]]
+; APPLE-NEXT:    [[RDX_2_NEXT_3]] = mul i32 [[RDX_2_NEXT_2]], [[TMP3]]
+; APPLE-NEXT:    [[IV_NEXT_3]] = add nuw nsw i64 [[IV]], 4
+; APPLE-NEXT:    [[EC_3:%.*]] = icmp eq i64 [[IV_NEXT_3]], 1024
+; APPLE-NEXT:    br i1 [[EC_3]], label %[[EXIT:.*]], label %[[LOOP]]
 ; APPLE:       [[EXIT]]:
-; APPLE-NEXT:    [[BIN_RDX3:%.*]] = phi i32 [ [[RDX_NEXT]], %[[LOOP]] ]
-; APPLE-NEXT:    [[RES_2:%.*]] = phi i32 [ [[RDX_2_NEXT]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RES_1:%.*]] = phi i32 [ [[RDX_NEXT_3]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RES_3:%.*]] = phi i32 [ [[RDX_2_NEXT_3]], %[[LOOP]] ]
 ; APPLE-NEXT:    [[SUM:%.*]] = add i32 [[BIN_RDX3]], [[RES_2]]
-; APPLE-NEXT:    ret i32 [[SUM]]
+; APPLE-NEXT:    [[BIN_RDX2:%.*]] = add i32 [[RDX_NEXT_2]], [[SUM]]
+; APPLE-NEXT:    [[BIN_RDX4:%.*]] = add i32 [[RDX_NEXT_3]], [[BIN_RDX2]]
+; APPLE-NEXT:    [[SUM1:%.*]] = add i32 [[BIN_RDX4]], [[RES_3]]
+; APPLE-NEXT:    ret i32 [[SUM1]]
 ;
 ; OTHER-LABEL: define i32 @test_add_and_mul_reduction_unroll_partial(
 ; OTHER-SAME: ptr [[A:%.*]], i64 noundef [[N:%.*]]) #[[ATTR0]] {
@@ -802,18 +841,72 @@ define i32 @test_add_reduction_runtime(ptr %a, i64 noundef %n) {
 ; APPLE-LABEL: define i32 @test_add_reduction_runtime(
 ; APPLE-SAME: ptr [[A:%.*]], i64 noundef [[N:%.*]]) #[[ATTR0]] {
 ; APPLE-NEXT:  [[ENTRY:.*]]:
+; APPLE-NEXT:    [[TMP0:%.*]] = add i64 [[N]], -1
+; APPLE-NEXT:    [[XTRAITER:%.*]] = and i64 [[N]], 3
+; APPLE-NEXT:    [[TMP1:%.*]] = icmp ult i64 [[TMP0]], 3
+; APPLE-NEXT:    br i1 [[TMP1]], label %[[EXIT_UNR_LCSSA:.*]], label %[[ENTRY_NEW:.*]]
+; APPLE:       [[ENTRY_NEW]]:
+; APPLE-NEXT:    [[UNROLL_ITER:%.*]] = sub i64 [[N]], [[XTRAITER]]
 ; APPLE-NEXT:    br label %[[LOOP:.*]]
 ; APPLE:       [[LOOP]]:
-; APPLE-NEXT:    [[IV_EPIL:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT_EPIL:%.*]], %[[LOOP]] ]
-; APPLE-NEXT:    [[RDX_EPIL:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[RDX_NEXT_EPIL:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[IV_EPIL:%.*]] = phi i64 [ 0, %[[ENTRY_NEW]] ], [ [[IV_NEXT_3:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_1:%.*]] = phi i32 [ 0, %[[ENTRY_NEW]] ], [ [[RDX_NEXT_1:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_2:%.*]] = phi i32 [ 0, %[[ENTRY_NEW]] ], [ [[RDX_NEXT_2:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_3:%.*]] = phi i32 [ 0, %[[ENTRY_NEW]] ], [ [[RDX_NEXT_3:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX:%.*]] = phi i32 [ 0, %[[ENTRY_NEW]] ], [ [[RDX_NEXT:%.*]], %[[LOOP]] ]
+; APPLE-NEXT:    [[NITER:%.*]] = phi i64 [ 0, %[[ENTRY_NEW]] ], [ [[NITER_NEXT_3:%.*]], %[[LOOP]] ]
 ; APPLE-NEXT:    [[GEP_A_EPIL:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_EPIL]]
 ; APPLE-NEXT:    [[TMP6:%.*]] = load i32, ptr [[GEP_A_EPIL]], align 2
-; APPLE-NEXT:    [[RDX_NEXT_EPIL]] = add nuw nsw i32 [[RDX_EPIL]], [[TMP6]]
-; APPLE-NEXT:    [[IV_NEXT_EPIL]] = add nuw nsw i64 [[IV_EPIL]], 1
+; APPLE-NEXT:    [[RDX_NEXT]] = add i32 [[RDX]], [[TMP6]]
+; APPLE-NEXT:    [[IV_NEXT:%.*]] = add nuw nsw i64 [[IV_EPIL]], 1
+; APPLE-NEXT:    [[GEP_A_1:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT]]
+; APPLE-NEXT:    [[TMP3:%.*]] = load i32, ptr [[GEP_A_1]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_1]] = add i32 [[RDX_1]], [[TMP3]]
+; APPLE-NEXT:    [[IV_NEXT_1:%.*]] = add nuw nsw i64 [[IV_EPIL]], 2
+; APPLE-NEXT:    [[GEP_A_2:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT_1]]
+; APPLE-NEXT:    [[TMP4:%.*]] = load i32, ptr [[GEP_A_2]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_2]] = add i32 [[RDX_2]], [[TMP4]]
+; APPLE-NEXT:    [[IV_NEXT_2:%.*]] = add nuw nsw i64 [[IV_EPIL]], 3
+; APPLE-NEXT:    [[GEP_A_3:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_NEXT_2]]
+; APPLE-NEXT:    [[TMP5:%.*]] = load i32, ptr [[GEP_A_3]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_3]] = add i32 [[RDX_3]], [[TMP5]]
+; APPLE-NEXT:    [[IV_NEXT_3]] = add nuw nsw i64 [[IV_EPIL]], 4
+; APPLE-NEXT:    [[NITER_NEXT_3]] = add nuw i64 [[NITER]], 4
+; APPLE-NEXT:    [[NITER_NCMP_3:%.*]] = icmp eq i64 [[NITER_NEXT_3]], [[UNROLL_ITER]]
+; APPLE-NEXT:    br i1 [[NITER_NCMP_3]], label %[[EXIT_UNR_LCSSA_LOOPEXIT:.*]], label %[[LOOP]]
+; APPLE:       [[EXIT_UNR_LCSSA_LOOPEXIT]]:
+; APPLE-NEXT:    [[RES_PH_PH:%.*]] = phi i32 [ [[RDX_NEXT_3]], %[[LOOP]] ]
+; APPLE-NEXT:    [[IV_UNR_PH:%.*]] = phi i64 [ [[IV_NEXT_3]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RDX_UNR_PH:%.*]] = phi i32 [ [[RDX_NEXT_3]], %[[LOOP]] ]
+; APPLE-NEXT:    [[BIN_RDX:%.*]] = add i32 [[RDX_NEXT_1]], [[RDX_NEXT]]
+; APPLE-NEXT:    [[BIN_RDX2:%.*]] = add i32 [[RDX_NEXT_2]], [[BIN_RDX]]
+; APPLE-NEXT:    [[BIN_RDX3:%.*]] = add i32 [[RDX_NEXT_3]], [[BIN_RDX2]]
+; APPLE-NEXT:    br label %[[EXIT_UNR_LCSSA]]
+; APPLE:       [[EXIT_UNR_LCSSA]]:
+; APPLE-NEXT:    [[RES_PH:%.*]] = phi i32 [ poison, %[[ENTRY]] ], [ [[BIN_RDX3]], %[[EXIT_UNR_LCSSA_LOOPEXIT]] ]
+; APPLE-NEXT:    [[IV_UNR:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_UNR_PH]], %[[EXIT_UNR_LCSSA_LOOPEXIT]] ]
+; APPLE-NEXT:    [[RDX_UNR:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[BIN_RDX3]], %[[EXIT_UNR_LCSSA_LOOPEXIT]] ]
+; APPLE-NEXT:    [[LCMP_MOD:%.*]] = icmp ne i64 [[XTRAITER]], 0
+; APPLE-NEXT:    br i1 [[LCMP_MOD]], label %[[LOOP_EPIL_PREHEADER:.*]], label %[[EXIT:.*]]
+; APPLE:       [[LOOP_EPIL_PREHEADER]]:
+; APPLE-NEXT:    br label %[[LOOP_EPIL:.*]]
+; APPLE:       [[LOOP_EPIL]]:
+; APPLE-NEXT:    [[IV_EPIL1:%.*]] = phi i64 [ [[IV_UNR]], %[[LOOP_EPIL_PREHEADER]] ], [ [[IV_NEXT_EPIL:%.*]], %[[LOOP_EPIL]] ]
+; APPLE-NEXT:    [[RDX_EPIL:%.*]] = phi i32 [ [[RDX_UNR]], %[[LOOP_EPIL_PREHEADER]] ], [ [[RDX_NEXT_EPIL:%.*]], %[[LOOP_EPIL]] ]
+; APPLE-NEXT:    [[EPIL_ITER:%.*]] = phi i64 [ 0, %[[LOOP_EPIL_PREHEADER]] ], [ [[EPIL_ITER_NEXT:%.*]], %[[LOOP_EPIL]] ]
+; APPLE-NEXT:    [[GEP_A_EPIL1:%.*]] = getelementptr inbounds nuw i32, ptr [[A]], i64 [[IV_EPIL1]]
+; APPLE-NEXT:    [[TMP7:%.*]] = load i32, ptr [[GEP_A_EPIL1]], align 2
+; APPLE-NEXT:    [[RDX_NEXT_EPIL]] = add nuw nsw i32 [[RDX_EPIL]], [[TMP7]]
+; APPLE-NEXT:    [[IV_NEXT_EPIL]] = add nuw nsw i64 [[IV_EPIL1]], 1
 ; APPLE-NEXT:    [[EC_EPIL:%.*]] = icmp eq i64 [[IV_NEXT_EPIL]], [[N]]
-; APPLE-NEXT:    br i1 [[EC_EPIL]], label %[[EXIT:.*]], label %[[LOOP]]
+; APPLE-NEXT:    [[EPIL_ITER_NEXT]] = add i64 [[EPIL_ITER]], 1
+; APPLE-NEXT:    [[EPIL_ITER_CMP:%.*]] = icmp ne i64 [[EPIL_ITER_NEXT]], [[XTRAITER]]
+; APPLE-NEXT:    br i1 [[EPIL_ITER_CMP]], label %[[LOOP_EPIL]], label %[[EXIT_EPILOG_LCSSA:.*]], !llvm.loop [[LOOP3:![0-9]+]]
+; APPLE:       [[EXIT_EPILOG_LCSSA]]:
+; APPLE-NEXT:    [[RES_PH1:%.*]] = phi i32 [ [[RDX_NEXT_EPIL]], %[[LOOP_EPIL]] ]
+; APPLE-NEXT:    br label %[[EXIT]]
 ; APPLE:       [[EXIT]]:
-; APPLE-NEXT:    [[RES:%.*]] = phi i32 [ [[RDX_NEXT_EPIL]], %[[LOOP]] ]
+; APPLE-NEXT:    [[RES:%.*]] = phi i32 [ [[RES_PH]], %[[EXIT_UNR_LCSSA]] ], [ [[RES_PH1]], %[[EXIT_EPILOG_LCSSA]] ]
 ; APPLE-NEXT:    ret i32 [[RES]]
 ;
 ; OTHER-LABEL: define i32 @test_add_reduction_runtime(
@@ -908,6 +1001,7 @@ exit:
 ; APPLE: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]]}
 ; APPLE: [[META1]] = !{!"llvm.loop.unroll.disable"}
 ; APPLE: [[LOOP2]] = distinct !{[[LOOP2]], [[META1]]}
+; APPLE: [[LOOP3]] = distinct !{[[LOOP3]], [[META1]]}
 ;.
 ; OTHER: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]]}
 ; OTHER: [[META1]] = !{!"llvm.loop.unroll.disable"}