[SLP] Fix for PR32036: Vectorized horizontal reduction returning wrong

result

Summary:
If the same value is used several times as an extra value, SLP
vectorizer takes it into account only once instead of actual number of
using.
For example:
```
int val = 1;
for (int y = 0; y < 8; y++) {
  for (int x = 0; x < 8; x++) {
    val = val + input[y * 8 + x] + 3;
  }
}
```
We have 2 extra rguments: `1` - initial value of horizontal reduction
and `3`, which is added 8*8 times to the reduction. Before the patch we
added `1` to the reduction value and added once `3`, though it must be
added 64 times.

Reviewers: mkuper, mzolotukhin

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30262

llvm-svn: 295949

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -304,6 +304,7 @@ public:
   typedef SmallVector<Instruction *, 16> InstrList;
   typedef SmallPtrSet<Value *, 16> ValueSet;
   typedef SmallVector<StoreInst *, 8> StoreList;
+  typedef MapVector<Value *, std::vector<DebugLoc>> ExtraValueToDebugLocsMap;
 
   BoUpSLP(Function *Func, ScalarEvolution *Se, TargetTransformInfo *Tti,
           TargetLibraryInfo *TLi, AliasAnalysis *Aa, LoopInfo *Li,
@@ -333,7 +334,7 @@ public:
   /// Vectorize the tree but with the list of externally used values \p
   /// ExternallyUsedValues. Values in this MapVector can be replaced but the
   /// generated extractvalue instructions.
-  Value *vectorizeTree(MapVector<Value *, DebugLoc> &ExternallyUsedValues);
+  Value *vectorizeTree(ExtraValueToDebugLocsMap &ExternallyUsedValues);
 
   /// \returns the cost incurred by unwanted spills and fills, caused by
   /// holding live values over call sites.
@@ -352,7 +353,7 @@ public:
   /// into account (anf updating it, if required) list of externally used
   /// values stored in \p ExternallyUsedValues.
   void buildTree(ArrayRef<Value *> Roots,
-                 MapVector<Value *, DebugLoc> &ExternallyUsedValues,
+                 ExtraValueToDebugLocsMap &ExternallyUsedValues,
                  ArrayRef<Value *> UserIgnoreLst = None);
 
   /// Clear the internal data structures that are created by 'buildTree'.
@@ -953,11 +954,11 @@ private:
 
 void BoUpSLP::buildTree(ArrayRef<Value *> Roots,
                         ArrayRef<Value *> UserIgnoreLst) {
-  MapVector<Value *, DebugLoc> ExternallyUsedValues;
+  ExtraValueToDebugLocsMap ExternallyUsedValues;
   buildTree(Roots, ExternallyUsedValues, UserIgnoreLst);
 }
 void BoUpSLP::buildTree(ArrayRef<Value *> Roots,
-                        MapVector<Value *, DebugLoc> &ExternallyUsedValues,
+                        ExtraValueToDebugLocsMap &ExternallyUsedValues,
                         ArrayRef<Value *> UserIgnoreLst) {
   deleteTree();
   UserIgnoreList = UserIgnoreLst;
@@ -2801,12 +2802,12 @@ Value *BoUpSLP::vectorizeTree(ArrayRef<Value *> VL, TreeEntry *E) {
 }
 
 Value *BoUpSLP::vectorizeTree() {
-  MapVector<Value *, DebugLoc> ExternallyUsedValues;
+  ExtraValueToDebugLocsMap ExternallyUsedValues;
   return vectorizeTree(ExternallyUsedValues);
 }
 
 Value *
-BoUpSLP::vectorizeTree(MapVector<Value *, DebugLoc> &ExternallyUsedValues) {
+BoUpSLP::vectorizeTree(ExtraValueToDebugLocsMap &ExternallyUsedValues) {
 
   // All blocks must be scheduled before any instructions are inserted.
   for (auto &BSIter : BlocksSchedules) {
@@ -2868,7 +2869,6 @@ BoUpSLP::vectorizeTree(MapVector<Value *, DebugLoc> &ExternallyUsedValues) {
       assert(ExternallyUsedValues.count(Scalar) &&
              "Scalar with nullptr as an external user must be registered in "
              "ExternallyUsedValues map");
-      DebugLoc DL = ExternallyUsedValues[Scalar];
       if (auto *VecI = dyn_cast<Instruction>(Vec)) {
         Builder.SetInsertPoint(VecI->getParent(),
                                std::next(VecI->getIterator()));
@@ -2878,8 +2878,8 @@ BoUpSLP::vectorizeTree(MapVector<Value *, DebugLoc> &ExternallyUsedValues) {
       Value *Ex = Builder.CreateExtractElement(Vec, Lane);
       Ex = extend(ScalarRoot, Ex, Scalar->getType());
       CSEBlocks.insert(cast<Instruction>(Scalar)->getParent());
+      std::swap(ExternallyUsedValues[Ex], ExternallyUsedValues[Scalar]);
       ExternallyUsedValues.erase(Scalar);
-      ExternallyUsedValues[Ex] = DL;
       continue;
     }
 
@@ -4439,9 +4439,11 @@ public:
     Builder.setFastMathFlags(Unsafe);
     unsigned i = 0;
 
-    MapVector<Value *, DebugLoc> ExternallyUsedValues;
+    BoUpSLP::ExtraValueToDebugLocsMap ExternallyUsedValues;
+    // The same extra argument may be used several time, so log each attempt
+    // to use it.
     for (auto &Pair : ExtraArgs)
-      ExternallyUsedValues[Pair.second] = Pair.first->getDebugLoc();
+      ExternallyUsedValues[Pair.second].push_back(Pair.first->getDebugLoc());
     while (i < NumReducedVals - ReduxWidth + 1 && ReduxWidth > 2) {
       auto VL = makeArrayRef(&ReducedVals[i], ReduxWidth);
       V.buildTree(VL, ExternallyUsedValues, ReductionOps);
@@ -4489,10 +4491,14 @@ public:
             Builder.CreateBinOp(ReductionOpcode, VectorizedTree, I);
       }
       for (auto &Pair : ExternallyUsedValues) {
-        Builder.SetCurrentDebugLocation(Pair.second);
+        // Add each externally used value to the final reduction.
+        assert(!Pair.second.empty() && "At least one DebugLoc must be added.");
+        for (auto &DL : Pair.second) {
+          Builder.SetCurrentDebugLocation(DL);
           VectorizedTree = Builder.CreateBinOp(ReductionOpcode, VectorizedTree,
                                                Pair.first, "bin.extra");
         }
+      }
       // Update users.
       if (ReductionPHI && !isa<UndefValue>(ReductionPHI)) {
         assert(ReductionRoot && "Need a reduction operation");

llvm/test/Transforms/SLPVectorizer/X86/horizontal-list.ll

@@ -1473,9 +1473,10 @@ define float @extra_args_same_several_times(float* nocapture readonly %x, i32 %a
 ; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <8 x float> [[BIN_RDX4]], i32 0
 ; CHECK-NEXT:    [[BIN_EXTRA:%.*]] = fadd fast float [[TMP2]], [[ADD]]
 ; CHECK-NEXT:    [[BIN_EXTRA5:%.*]] = fadd fast float [[BIN_EXTRA]], 5.000000e+00
-; CHECK-NEXT:    [[BIN_EXTRA6:%.*]] = fadd fast float [[BIN_EXTRA5]], [[CONV]]
+; CHECK-NEXT:    [[BIN_EXTRA6:%.*]] = fadd fast float [[BIN_EXTRA5]], 5.000000e+00
+; CHECK-NEXT:    [[BIN_EXTRA7:%.*]] = fadd fast float [[BIN_EXTRA6]], [[CONV]]
 ; CHECK-NEXT:    [[ADD4_6:%.*]] = fadd fast float undef, [[ADD4_5]]
-; CHECK-NEXT:    ret float [[BIN_EXTRA6]]
+; CHECK-NEXT:    ret float [[BIN_EXTRA7]]
 ;
 ; THRESHOLD-LABEL: @extra_args_same_several_times(
 ; THRESHOLD-NEXT:  entry:
@@ -1510,9 +1511,10 @@ define float @extra_args_same_several_times(float* nocapture readonly %x, i32 %a
 ; THRESHOLD-NEXT:    [[TMP2:%.*]] = extractelement <8 x float> [[BIN_RDX4]], i32 0
 ; THRESHOLD-NEXT:    [[BIN_EXTRA:%.*]] = fadd fast float [[TMP2]], [[ADD]]
 ; THRESHOLD-NEXT:    [[BIN_EXTRA5:%.*]] = fadd fast float [[BIN_EXTRA]], 5.000000e+00
-; THRESHOLD-NEXT:    [[BIN_EXTRA6:%.*]] = fadd fast float [[BIN_EXTRA5]], [[CONV]]
+; THRESHOLD-NEXT:    [[BIN_EXTRA6:%.*]] = fadd fast float [[BIN_EXTRA5]], 5.000000e+00
+; THRESHOLD-NEXT:    [[BIN_EXTRA7:%.*]] = fadd fast float [[BIN_EXTRA6]], [[CONV]]
 ; THRESHOLD-NEXT:    [[ADD4_6:%.*]] = fadd fast float undef, [[ADD4_5]]
-; THRESHOLD-NEXT:    ret float [[BIN_EXTRA6]]
+; THRESHOLD-NEXT:    ret float [[BIN_EXTRA7]]
 ;
   entry:
   %mul = mul nsw i32 %b, %a