[SLP] Stop counting cost of gather sequences with multiple uses

When building the SLP tree, we look for reuse among the vectorized tree
entries. However, each gather sequence is represented by a unique tree entry,
even though the sequence may be identical to another one. This means, for
example, that a gather sequence with two uses will be counted twice when
computing the cost of the tree. We should only count the cost of the definition
of a gather sequence rather than its uses. During code generation, the
redundant gather sequences are emitted, but we optimize them away with CSE. So
it looks like this problem just affects the cost model.

Differential Revision: https://reviews.llvm.org/D44742

llvm-svn: 328316

diff --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index b21a9e0250ae28bfb54743396bccddc6e3502d28..af74acb415042b235c03540095e04d3effe56107 100644 (file)
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -2457,7 +2457,28 @@ int BoUpSLP::getTreeCost() {
 
   unsigned BundleWidth = VectorizableTree[0].Scalars.size();
 
-  for (TreeEntry &TE : VectorizableTree) {
+  for (unsigned I = 0, E = VectorizableTree.size(); I < E; ++I) {
+    TreeEntry &TE = VectorizableTree[I];
+
+    // We create duplicate tree entries for gather sequences that have multiple
+    // uses. However, we should not compute the cost of duplicate sequences.
+    // For example, if we have a build vector (i.e., insertelement sequence)
+    // that is used by more than one vector instruction, we only need to
+    // compute the cost of the insertelement instructions once. The redundent
+    // instructions will be eliminated by CSE.
+    //
+    // We should consider not creating duplicate tree entries for gather
+    // sequences, and instead add additional edges to the tree representing
+    // their uses. Since such an approach results in fewer total entries,
+    // existing heuristics based on tree size may yeild different results.
+    //
+    if (TE.NeedToGather &&
+        std::any_of(std::next(VectorizableTree.begin(), I + 1),
+                    VectorizableTree.end(), [TE](TreeEntry &Entry) {
+                      return Entry.NeedToGather && Entry.isSame(TE.Scalars);
+                    }))
+      continue;
+
     int C = getEntryCost(&TE);
     DEBUG(dbgs() << "SLP: Adding cost " << C << " for bundle that starts with "
                  << *TE.Scalars[0] << ".\n");

diff --git a/llvm/test/Transforms/SLPVectorizer/AArch64/gather-cost.ll b/llvm/test/Transforms/SLPVectorizer/AArch64/gather-cost.ll
index aec33c57160a04c3960e3d5f13236780c4d20000..a4c655ca3cb0b74d99ac09829dbfe3698cda6187 100644 (file)
--- a/llvm/test/Transforms/SLPVectorizer/AArch64/gather-cost.ll
+++ b/llvm/test/Transforms/SLPVectorizer/AArch64/gather-cost.ll
@@ -7,36 +7,22 @@ target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 target triple = "aarch64--linux-gnu"
 
 ; CHECK-LABEL:  @gather_multiple_use(
-; CHECK-NEXT:     [[TMP00:%.*]] = lshr i32 [[A:%.*]], 15
-; CHECK-NEXT:     [[TMP01:%.*]] = and i32 [[TMP00]], 65537
-; CHECK-NEXT:     [[TMP02:%.*]] = mul nuw i32 [[TMP01]], 65535
-; CHECK-NEXT:     [[TMP03:%.*]] = add i32 [[TMP02]], [[A]]
-; CHECK-NEXT:     [[TMP04:%.*]] = xor i32 [[TMP03]], [[TMP02]]
-; CHECK-NEXT:     [[TMP05:%.*]] = lshr i32 [[C:%.*]], 15
-; CHECK-NEXT:     [[TMP06:%.*]] = and i32 [[TMP05]], 65537
-; CHECK-NEXT:     [[TMP07:%.*]] = mul nuw i32 [[TMP06]], 65535
-; CHECK-NEXT:     [[TMP08:%.*]] = add i32 [[TMP07]], [[C]]
-; CHECK-NEXT:     [[TMP09:%.*]] = xor i32 [[TMP08]], [[TMP07]]
-; CHECK-NEXT:     [[TMP10:%.*]] = lshr i32 [[B:%.*]], 15
-; CHECK-NEXT:     [[TMP11:%.*]] = and i32 [[TMP10]], 65537
-; CHECK-NEXT:     [[TMP12:%.*]] = mul nuw i32 [[TMP11]], 65535
-; CHECK-NEXT:     [[TMP13:%.*]] = add i32 [[TMP12]], [[B]]
-; CHECK-NEXT:     [[TMP14:%.*]] = xor i32 [[TMP13]], [[TMP12]]
-; CHECK-NEXT:     [[TMP15:%.*]] = lshr i32 [[D:%.*]], 15
-; CHECK-NEXT:     [[TMP16:%.*]] = and i32 [[TMP15]], 65537
-; CHECK-NEXT:     [[TMP17:%.*]] = mul nuw i32 [[TMP16]], 65535
-; CHECK-NEXT:     [[TMP18:%.*]] = add i32 [[TMP17]], [[D]]
-; CHECK-NEXT:     [[TMP19:%.*]] = xor i32 [[TMP18]], [[TMP17]]
-; CHECK-NEXT:     [[TMP20:%.*]] = add i32 [[TMP09]], [[TMP04]]
-; CHECK-NEXT:     [[TMP21:%.*]] = add i32 [[TMP20]], [[TMP14]]
-; CHECK-NEXT:     [[TMP22:%.*]] = add i32 [[TMP21]], [[TMP19]]
-; CHECK-NEXT:     ret i32 [[TMP22]]
+; CHECK-NEXT:     [[TMP1:%.*]] = insertelement <4 x i32> undef, i32 [[C:%.*]], i32 0
+; CHECK-NEXT:     [[TMP2:%.*]] = insertelement <4 x i32> [[TMP1]], i32 [[A:%.*]], i32 1
+; CHECK-NEXT:     [[TMP3:%.*]] = insertelement <4 x i32> [[TMP2]], i32 [[B:%.*]], i32 2
+; CHECK-NEXT:     [[TMP4:%.*]] = insertelement <4 x i32> [[TMP3]], i32 [[D:%.*]], i32 3
+; CHECK-NEXT:     [[TMP5:%.*]] = lshr <4 x i32> [[TMP4]], <i32 15, i32 15, i32 15, i32 15>
+; CHECK-NEXT:     [[TMP6:%.*]] = and <4 x i32> [[TMP5]], <i32 65537, i32 65537, i32 65537, i32 65537>
+; CHECK-NEXT:     [[TMP7:%.*]] = mul nuw <4 x i32> [[TMP6]], <i32 65535, i32 65535, i32 65535, i32 65535>
+; CHECK-NEXT:     [[TMP8:%.*]] = add <4 x i32> [[TMP4]], [[TMP7]]
+; CHECK-NEXT:     [[TMP9:%.*]] = xor <4 x i32> [[TMP8]], [[TMP7]]
+; CHECK-NEXT:     [[TMP10:%.*]] = call i32 @llvm.experimental.vector.reduce.add.i32.v4i32(<4 x i32> [[TMP9]])
+; CHECK-NEXT:     ret i32 [[TMP10]]
 ;
 ; REMARK-LABEL: Function: gather_multiple_use
 ; REMARK:       Args:
-; REMARK-NEXT:    - String: Vectorizing horizontal reduction is possible
-; REMARK-NEXT:    - String: 'but not beneficial with cost '
-; REMARK-NEXT:    - Cost: '2'
+; REMARK-NEXT:    - String: 'Vectorized horizontal reduction with cost '
+; REMARK-NEXT:    - Cost: '-7'
 ;
 define internal i32 @gather_multiple_use(i32 %a, i32 %b, i32 %c, i32 %d) {
   %tmp00 = lshr i32 %a, 15

diff --git a/llvm/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll b/llvm/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll
index 00ac87d6a997be339c2752e481482cb4d136fbe9..54dbc13934e46eae5b5854eb1eb52520542074b6 100644 (file)
--- a/llvm/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll
+++ b/llvm/test/Transforms/SLPVectorizer/X86/blending-shuffle.ll
@@ -141,15 +141,16 @@ define i8 @k_bb(<4 x i8> %x) {
 ; CHECK-NEXT:    br label [[BB1:%.*]]
 ; CHECK:       bb1:
 ; CHECK-NEXT:    [[X3:%.*]] = extractelement <4 x i8> [[X]], i32 3
+; CHECK-NEXT:    [[X1:%.*]] = extractelement <4 x i8> [[X]], i32 1
+; CHECK-NEXT:    [[X2:%.*]] = extractelement <4 x i8> [[X]], i32 2
 ; CHECK-NEXT:    [[X0X0:%.*]] = mul i8 [[X0]], [[X0]]
 ; CHECK-NEXT:    [[X3X3:%.*]] = mul i8 [[X3]], [[X3]]
-; CHECK-NEXT:    [[TMP1:%.*]] = mul <4 x i8> [[X]], [[X]]
-; CHECK-NEXT:    [[TMP2:%.*]] = add i8 [[X0X0]], [[X3X3]]
-; CHECK-NEXT:    [[TMP3:%.*]] = extractelement <4 x i8> [[TMP1]], i32 1
-; CHECK-NEXT:    [[TMP4:%.*]] = extractelement <4 x i8> [[TMP1]], i32 2
-; CHECK-NEXT:    [[TMP5:%.*]] = add i8 [[TMP3]], [[TMP4]]
-; CHECK-NEXT:    [[TMP6:%.*]] = sdiv i8 [[TMP2]], [[TMP5]]
-; CHECK-NEXT:    ret i8 [[TMP6]]
+; CHECK-NEXT:    [[X1X1:%.*]] = mul i8 [[X1]], [[X1]]
+; CHECK-NEXT:    [[X2X2:%.*]] = mul i8 [[X2]], [[X2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[X0X0]], [[X3X3]]
+; CHECK-NEXT:    [[TMP2:%.*]] = add i8 [[X1X1]], [[X2X2]]
+; CHECK-NEXT:    [[TMP3:%.*]] = sdiv i8 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    ret i8 [[TMP3]]
 ;
   %x0 = extractelement <4 x i8> %x, i32 0
   br label %bb1