[llvm] 37bde7a - [SLP]Fix hanging on small trees with phis only with adjusted cost threshold

[Alexey Bataev via llvm-commits]

Author: Alexey Bataev
Date: 2025-02-18T07:56:47-08:00
New Revision: 37bde7ae5baa85889c9fcc647bdac149c646116e

URL: https://github.com/llvm/llvm-project/commit/37bde7ae5baa85889c9fcc647bdac149c646116e
DIFF: https://github.com/llvm/llvm-project/commit/37bde7ae5baa85889c9fcc647bdac149c646116e.diff

LOG: [SLP]Fix hanging on small trees with phis only with adjusted cost threshold

Need to check if the tree is too small before attempting to vectorize the tree to prevent hanging on small trees with phis only.

Added: 
    llvm/test/Transforms/SLPVectorizer/RISCV/small-phi-tree.ll

Modified: 
    llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index e946620406c2e..703fc7e3f9fa2 100644
--- a/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -12130,6 +12130,30 @@ bool BoUpSLP::isTreeTinyAndNotFullyVectorizable(bool ForReduction) const {
       }))
     return true;
 
+  // Do not vectorize small tree of phis only, if all vector phis are also
+  // gathered.
+  if (!ForReduction && SLPCostThreshold.getNumOccurrences() &&
+      VectorizableTree.size() <= Limit &&
+      all_of(VectorizableTree,
+             [&](const std::unique_ptr<TreeEntry> &TE) {
+               return (TE->isGather() &&
+                       (!TE->hasState() ||
+                        TE->getOpcode() != Instruction::ExtractElement) &&
+                       count_if(TE->Scalars, IsaPred<ExtractElementInst>) <=
+                           Limit) ||
+                      (TE->hasState() &&
+                       (TE->getOpcode() == Instruction::InsertElement ||
+                        (TE->getOpcode() == Instruction::PHI &&
+                         all_of(TE->Scalars, [&](Value *V) {
+                           return isa<PoisonValue>(V) || MustGather.contains(V);
+                         }))));
+             }) &&
+      any_of(VectorizableTree, [&](const std::unique_ptr<TreeEntry> &TE) {
+        return TE->State == TreeEntry::Vectorize &&
+               TE->getOpcode() == Instruction::PHI;
+      }))
+    return true;
+
   // We can vectorize the tree if its size is greater than or equal to the
   // minimum size specified by the MinTreeSize command line option.
   if (VectorizableTree.size() >= MinTreeSize)

diff  --git a/llvm/test/Transforms/SLPVectorizer/RISCV/small-phi-tree.ll b/llvm/test/Transforms/SLPVectorizer/RISCV/small-phi-tree.ll
new file mode 100644
index 0000000000000..c4f35d8dfc219
--- /dev/null
+++ b/llvm/test/Transforms/SLPVectorizer/RISCV/small-phi-tree.ll
@@ -0,0 +1,40 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -mtriple=riscv64 -mcpu=sifive-x280 -passes=slp-vectorizer -S -slp-threshold=-11 < %s | FileCheck %s
+
+define float @test(ptr %call78) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = insertelement <2 x ptr> <ptr null, ptr poison>, ptr [[CALL78:%.*]], i32 1
+; CHECK-NEXT:    br label [[FOR_BODY194:%.*]]
+; CHECK:       for.body194:
+; CHECK-NEXT:    [[INDVARS_IV132:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ 0, [[FOR_BODY194]] ]
+; CHECK-NEXT:    [[CURRENTW_031:%.*]] = phi ptr [ [[CALL78]], [[ENTRY]] ], [ [[PREVIOUSW_030:%.*]], [[FOR_BODY194]] ]
+; CHECK-NEXT:    [[PREVIOUSW_030]] = phi ptr [ null, [[ENTRY]] ], [ [[CURRENTW_031]], [[FOR_BODY194]] ]
+; CHECK-NEXT:    [[TMP1:%.*]] = phi <2 x ptr> [ [[TMP0]], [[ENTRY]] ], [ [[TMP3:%.*]], [[FOR_BODY194]] ]
+; CHECK-NEXT:    store float 0.000000e+00, ptr [[CURRENTW_031]], align 4
+; CHECK-NEXT:    tail call void null(ptr [[PREVIOUSW_030]], ptr null, ptr null, i32 0, i32 0, ptr null, ptr null, i32 0)
+; CHECK-NEXT:    [[TMP2:%.*]] = insertelement <2 x ptr> poison, ptr [[CURRENTW_031]], i32 0
+; CHECK-NEXT:    [[TMP3]] = insertelement <2 x ptr> [[TMP2]], ptr [[PREVIOUSW_030]], i32 1
+; CHECK-NEXT:    br i1 false, label [[FOR_END286_LOOPEXIT:%.*]], label [[FOR_BODY194]]
+; CHECK:       for.end286.loopexit:
+; CHECK-NEXT:    [[TMP4:%.*]] = phi <2 x ptr> [ [[TMP1]], [[FOR_BODY194]] ]
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+entry:
+  br label %for.body194
+
+for.body194:
+  %indvars.iv132 = phi i64 [ 0, %entry ], [ 0, %for.body194 ]
+  %currentw.031 = phi ptr [ %call78, %entry ], [ %previousw.030, %for.body194 ]
+  %previousw.030 = phi ptr [ null, %entry ], [ %currentw.031, %for.body194 ]
+  store float 0.000000e+00, ptr %currentw.031, align 4
+  tail call void null(ptr %previousw.030, ptr null, ptr null, i32 0, i32 0, ptr null, ptr null, i32 0)
+  br i1 false, label %for.end286.loopexit, label %for.body194
+
+for.end286.loopexit:
+  %currentw.031.lcssa = phi ptr [ %currentw.031, %for.body194 ]
+  %previousw.030.lcssa = phi ptr [ %previousw.030, %for.body194 ]
+  ret float 0.000000e+00
+}
+
+