[SLP]Attempt to vectorize long stores, if short one failed.

[alexey-bataev]

We can try to vectorize long store sequences, if short ones were
unsuccessful because of the non-profitable vectorization. It should not
increase compile time significantly (stores are sorted already,
complexity is n x log n), but vectorize extra code.

Metric: size..text

Program size..text
results results0 diff
test-suite :: External/SPEC/CINT2006/400.perlbench/400.perlbench.test 1088012.00 1088236.00 0.0%
test-suite :: SingleSource/UnitTests/matrix-types-spec.test 480396.00 480476.00 0.0%
test-suite :: External/SPEC/CINT2017rate/525.x264_r/525.x264_r.test 664613.00 664661.00 0.0%
test-suite :: External/SPEC/CINT2017speed/625.x264_s/625.x264_s.test 664613.00 664661.00 0.0%
test-suite :: External/SPEC/CFP2017rate/510.parest_r/510.parest_r.test 2041105.00 2040961.00 -0.0%
test-suite :: MultiSource/Applications/JM/lencod/lencod.test 836563.00 836387.00 -0.0%
test-suite :: MultiSource/Benchmarks/7zip/7zip-benchmark.test 1035100.00 1032140.00 -0.3%

In all benchmarks extra code gets vectorized

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Alexey Bataev (alexey-bataev)

Changes

We can try to vectorize long store sequences, if short ones were
unsuccessful because of the non-profitable vectorization. It should not
increase compile time significantly (stores are sorted already,
complexity is n x log n), but vectorize extra code.

Metric: size..text

Program size..text
results results0 diff
test-suite :: External/SPEC/CINT2006/400.perlbench/400.perlbench.test 1088012.00 1088236.00 0.0%
test-suite :: SingleSource/UnitTests/matrix-types-spec.test 480396.00 480476.00 0.0%
test-suite :: External/SPEC/CINT2017rate/525.x264_r/525.x264_r.test 664613.00 664661.00 0.0%
test-suite :: External/SPEC/CINT2017speed/625.x264_s/625.x264_s.test 664613.00 664661.00 0.0%
test-suite :: External/SPEC/CFP2017rate/510.parest_r/510.parest_r.test 2041105.00 2040961.00 -0.0%
test-suite :: MultiSource/Applications/JM/lencod/lencod.test 836563.00 836387.00 -0.0%
test-suite :: MultiSource/Benchmarks/7zip/7zip-benchmark.test 1035100.00 1032140.00 -0.3%

In all benchmarks extra code gets vectorized

---

Full diff: https://github.com/llvm/llvm-project/pull/88563.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp (+51-30)
• (modified) llvm/test/Transforms/SLPVectorizer/X86/pr46983.ll (+11-35)

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index df891371fdf758..4f70490f5171cc 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -15111,39 +15111,60 @@ bool SLPVectorizerPass::vectorizeStores(ArrayRef<StoreInst *> Stores,
         Size /= 2;
       });
       unsigned StartIdx = 0;
-      for (unsigned Size : CandidateVFs) {
-        for (unsigned Cnt = StartIdx, E = Operands.size(); Cnt + Size <= E;) {
-          ArrayRef<Value *> Slice = ArrayRef(Operands).slice(Cnt, Size);
-          assert(
-              all_of(
-                  Slice,
-                  [&](Value *V) {
-                    return cast<StoreInst>(V)->getValueOperand()->getType() ==
-                           cast<StoreInst>(Slice.front())
-                               ->getValueOperand()
-                               ->getType();
-                  }) &&
-              "Expected all operands of same type.");
-          if (!VectorizedStores.count(Slice.front()) &&
-              !VectorizedStores.count(Slice.back()) &&
-              TriedSequences.insert(std::make_pair(Slice.front(), Slice.back()))
-                  .second &&
-              vectorizeStoreChain(Slice, R, Cnt, MinVF)) {
-            // Mark the vectorized stores so that we don't vectorize them again.
-            VectorizedStores.insert(Slice.begin(), Slice.end());
-            Changed = true;
-            // If we vectorized initial block, no need to try to vectorize it
-            // again.
-            if (Cnt == StartIdx)
-              StartIdx += Size;
-            Cnt += Size;
-            continue;
+      unsigned Repeat = 0;
+      constexpr unsigned MaxAttempts = 2;
+      while (true) {
+        ++Repeat;
+        for (unsigned Size : CandidateVFs) {
+          for (unsigned Cnt = StartIdx, E = Operands.size(); Cnt + Size <= E;) {
+            ArrayRef<Value *> Slice = ArrayRef(Operands).slice(Cnt, Size);
+            assert(
+                all_of(
+                    Slice,
+                    [&](Value *V) {
+                      return cast<StoreInst>(V)->getValueOperand()->getType() ==
+                             cast<StoreInst>(Slice.front())
+                                 ->getValueOperand()
+                                 ->getType();
+                    }) &&
+                "Expected all operands of same type.");
+            if (!VectorizedStores.count(Slice.front()) &&
+                !VectorizedStores.count(Slice.back()) &&
+                TriedSequences
+                    .insert(std::make_pair(Slice.front(), Slice.back()))
+                    .second &&
+                vectorizeStoreChain(Slice, R, Cnt, MinVF)) {
+              // Mark the vectorized stores so that we don't vectorize them
+              // again.
+              VectorizedStores.insert(Slice.begin(), Slice.end());
+              Changed = true;
+              // If we vectorized initial block, no need to try to vectorize
+              // it again.
+              if (Cnt == StartIdx)
+                StartIdx += Size;
+              Cnt += Size;
+              continue;
+            }
+            ++Cnt;
+          }
+          // Check if the whole array was vectorized already - exit.
+          if (StartIdx >= Operands.size()) {
+            Repeat = MaxAttempts;
+            break;
           }
-          ++Cnt;
         }
-        // Check if the whole array was vectorized already - exit.
-        if (StartIdx >= Operands.size())
+        // Check if tried all attempts or no need for the last attempts at all.
+        if (Repeat >= MaxAttempts)
           break;
+        const unsigned MaxTotalNum = bit_floor(Operands.size() - StartIdx);
+        if (MaxVF >= MaxTotalNum)
+          break;
+        // Last attempt to vectorize max number of elements, if all previous
+        // attempts were unsuccessful because of the cost issues.
+        CandidateVFs.clear();
+        for (unsigned Size = MaxTotalNum; Size > MaxVF; Size /= 2) {
+          CandidateVFs.push_back(Size);
+        }
       }
     }
   };
diff --git a/llvm/test/Transforms/SLPVectorizer/X86/pr46983.ll b/llvm/test/Transforms/SLPVectorizer/X86/pr46983.ll
index 75505f632a43f3..3deab0975ce764 100644
--- a/llvm/test/Transforms/SLPVectorizer/X86/pr46983.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/pr46983.ll
@@ -100,41 +100,17 @@ define void @store_i8(ptr nocapture %0, i32 %1, i32 %2) {
 define void @store_i64(ptr nocapture %0, i32 %1, i32 %2) {
 ; SSE-LABEL: @store_i64(
 ; SSE-NEXT:    [[TMP4:%.*]] = zext i32 [[TMP1:%.*]] to i64
-; SSE-NEXT:    [[TMP5:%.*]] = load i64, ptr [[TMP0:%.*]], align 8, !tbaa [[TBAA5:![0-9]+]]
-; SSE-NEXT:    [[TMP6:%.*]] = mul i64 [[TMP5]], [[TMP4]]
-; SSE-NEXT:    [[TMP7:%.*]] = lshr i64 [[TMP6]], 15
-; SSE-NEXT:    [[TMP8:%.*]] = trunc i64 [[TMP7]] to i32
-; SSE-NEXT:    [[TMP9:%.*]] = icmp ult i32 [[TMP8]], 255
-; SSE-NEXT:    [[TMP10:%.*]] = and i64 [[TMP7]], 4294967295
-; SSE-NEXT:    [[TMP11:%.*]] = select i1 [[TMP9]], i64 [[TMP10]], i64 255
-; SSE-NEXT:    store i64 [[TMP11]], ptr [[TMP0]], align 8, !tbaa [[TBAA5]]
-; SSE-NEXT:    [[TMP12:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 8
-; SSE-NEXT:    [[TMP13:%.*]] = load i64, ptr [[TMP12]], align 8, !tbaa [[TBAA5]]
-; SSE-NEXT:    [[TMP14:%.*]] = mul i64 [[TMP13]], [[TMP4]]
-; SSE-NEXT:    [[TMP15:%.*]] = lshr i64 [[TMP14]], 15
-; SSE-NEXT:    [[TMP16:%.*]] = trunc i64 [[TMP15]] to i32
-; SSE-NEXT:    [[TMP17:%.*]] = icmp ult i32 [[TMP16]], 255
-; SSE-NEXT:    [[TMP18:%.*]] = and i64 [[TMP15]], 4294967295
-; SSE-NEXT:    [[TMP19:%.*]] = select i1 [[TMP17]], i64 [[TMP18]], i64 255
-; SSE-NEXT:    store i64 [[TMP19]], ptr [[TMP12]], align 8, !tbaa [[TBAA5]]
-; SSE-NEXT:    [[TMP20:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 16
-; SSE-NEXT:    [[TMP21:%.*]] = load i64, ptr [[TMP20]], align 8, !tbaa [[TBAA5]]
-; SSE-NEXT:    [[TMP22:%.*]] = mul i64 [[TMP21]], [[TMP4]]
-; SSE-NEXT:    [[TMP23:%.*]] = lshr i64 [[TMP22]], 15
-; SSE-NEXT:    [[TMP24:%.*]] = trunc i64 [[TMP23]] to i32
-; SSE-NEXT:    [[TMP25:%.*]] = icmp ult i32 [[TMP24]], 255
-; SSE-NEXT:    [[TMP26:%.*]] = and i64 [[TMP23]], 4294967295
-; SSE-NEXT:    [[TMP27:%.*]] = select i1 [[TMP25]], i64 [[TMP26]], i64 255
-; SSE-NEXT:    store i64 [[TMP27]], ptr [[TMP20]], align 8, !tbaa [[TBAA5]]
-; SSE-NEXT:    [[TMP28:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 24
-; SSE-NEXT:    [[TMP29:%.*]] = load i64, ptr [[TMP28]], align 8, !tbaa [[TBAA5]]
-; SSE-NEXT:    [[TMP30:%.*]] = mul i64 [[TMP29]], [[TMP4]]
-; SSE-NEXT:    [[TMP31:%.*]] = lshr i64 [[TMP30]], 15
-; SSE-NEXT:    [[TMP32:%.*]] = trunc i64 [[TMP31]] to i32
-; SSE-NEXT:    [[TMP33:%.*]] = icmp ult i32 [[TMP32]], 255
-; SSE-NEXT:    [[TMP34:%.*]] = and i64 [[TMP31]], 4294967295
-; SSE-NEXT:    [[TMP35:%.*]] = select i1 [[TMP33]], i64 [[TMP34]], i64 255
-; SSE-NEXT:    store i64 [[TMP35]], ptr [[TMP28]], align 8, !tbaa [[TBAA5]]
+; SSE-NEXT:    [[TMP5:%.*]] = load <4 x i64>, ptr [[TMP0:%.*]], align 8, !tbaa [[TBAA5:![0-9]+]]
+; SSE-NEXT:    [[TMP6:%.*]] = insertelement <4 x i64> poison, i64 [[TMP4]], i64 0
+; SSE-NEXT:    [[TMP7:%.*]] = shufflevector <4 x i64> [[TMP6]], <4 x i64> poison, <4 x i32> zeroinitializer
+; SSE-NEXT:    [[TMP8:%.*]] = mul <4 x i64> [[TMP5]], [[TMP7]]
+; SSE-NEXT:    [[TMP9:%.*]] = lshr <4 x i64> [[TMP8]], <i64 15, i64 15, i64 15, i64 15>
+; SSE-NEXT:    [[TMP10:%.*]] = trunc <4 x i64> [[TMP9]] to <4 x i32>
+; SSE-NEXT:    [[TMP11:%.*]] = icmp ult <4 x i32> [[TMP10]], <i32 255, i32 255, i32 255, i32 255>
+; SSE-NEXT:    [[TMP12:%.*]] = trunc <4 x i64> [[TMP9]] to <4 x i32>
+; SSE-NEXT:    [[TMP13:%.*]] = select <4 x i1> [[TMP11]], <4 x i32> [[TMP12]], <4 x i32> <i32 255, i32 255, i32 255, i32 255>
+; SSE-NEXT:    [[TMP14:%.*]] = zext <4 x i32> [[TMP13]] to <4 x i64>
+; SSE-NEXT:    store <4 x i64> [[TMP14]], ptr [[TMP0]], align 8, !tbaa [[TBAA5]]
 ; SSE-NEXT:    ret void
 ;
 ; AVX-LABEL: @store_i64(

[alexey-bataev]

Ping!

[RKSimon]

LGTM

[nikic]

I've reverted this change due to large compile-time regressions (https://llvm-compile-time-tracker.com/compare.php?from=c7657cf7d1ee57f9cb9133164536591a1842b43c&to=7d4e8c1f3bbfe976f4871c9cf953f76d771b0eda&stat=instructions:u).

The regressions go up to 10% on individual files (https://llvm-compile-time-tracker.com/compare.php?from=c7657cf7d1ee57f9cb9133164536591a1842b43c&to=7d4e8c1f3bbfe976f4871c9cf953f76d771b0eda&stat=instructions%3Au&details=on). Though the 10% regressions are in LTO builds on small files, so easier to investigate is probably something like constants.c from pairlocalalign that regresses by 5% in a normal O3 build.

[nikic]

I've reverted the new version again -- it looks like the pairlocalalign regressions have been fixed, but all the other ones are still there (https://llvm-compile-time-tracker.com/compare.php?from=693a458287d019c5c6a66fe3019d099df2978cdb&to=6f7160eedb2db02f37d4ffd52fff7b0cf88b3fdc&stat=instructions:u)

For example libclamav_nsis_LZMADecode.c from clamscan has a 5-6% regression, transform8x8.c from lencod as well, Ppmd7.c from 7zip has 7%.

[nikic]

I've added your LLVM fork the the compile-time tracker, in case you want to test changes before landing them upstream.

[alexey-bataev]

I tried it locally and did not see significant compile time regressions, will double check tomorrow