[VPlan] Perform optimizeMaskToEVL in terms of pattern matching (#155394)

Currently in optimizeMaskToEVL we convert every widened load, store or
reduction to a VP predicated recipe with EVL, regardless of whether or
not it uses the header mask.

So currently we have to be careful when working on other parts VPlan to
make sure that the EVL transform doesn't break or transform something
incorrectly, because it's not a semantics preserving transform.
Forgetting to do so has caused miscompiles before, like the case that
was fixed in #113667

This PR rewrites it to work in terms of pattern matching, so it now only
converts a recipe to a VP predicated recipe if it is exactly masked with
the header mask.

After this the transform should be a true optimisation and not change
any semantics, so it shouldn't miscompile things if other parts of VPlan
change.

This fixes #152541, and allows us to move addExplicitVectorLength into
tryToBuildVPlanWithVPRecipes in #153144

It also splits out the load/store transforms into separate patterns for
reversed and non-reversed, which should make #146525 easier to implement
and reason about.

1 files changed, 79 insertions, 67 deletions

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index b45536869c5a..d67b31d28e3a 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -2528,90 +2528,102 @@ void VPlanTransforms::addActiveLaneMask(
   HeaderMask->eraseFromParent();
 }
 
+template <typename Op0_t, typename Op1_t> struct RemoveMask_match {
+  Op0_t In;
+  Op1_t &Out;
+
+  RemoveMask_match(const Op0_t &In, Op1_t &Out) : In(In), Out(Out) {}
+
+  template <typename OpTy> bool match(OpTy *V) const {
+    if (m_Specific(In).match(V)) {
+      Out = nullptr;
+      return true;
+    }
+    if (m_LogicalAnd(m_Specific(In), m_VPValue(Out)).match(V))
+      return true;
+    return false;
+  }
+};
+
+/// Match a specific mask \p In, or a combination of it (logical-and In, Out).
+/// Returns the remaining part \p Out if so, or nullptr otherwise.
+template <typename Op0_t, typename Op1_t>
+static inline RemoveMask_match<Op0_t, Op1_t> m_RemoveMask(const Op0_t &In,
+                                                          Op1_t &Out) {
+  return RemoveMask_match<Op0_t, Op1_t>(In, Out);
+}
+
 /// Try to optimize a \p CurRecipe masked by \p HeaderMask to a corresponding
 /// EVL-based recipe without the header mask. Returns nullptr if no EVL-based
 /// recipe could be created.
 /// \p HeaderMask  Header Mask.
 /// \p CurRecipe   Recipe to be transform.
 /// \p TypeInfo    VPlan-based type analysis.
-/// \p AllOneMask  The vector mask parameter of vector-predication intrinsics.
 /// \p EVL         The explicit vector length parameter of vector-predication
 /// intrinsics.
 static VPRecipeBase *optimizeMaskToEVL(VPValue *HeaderMask,
                                        VPRecipeBase &CurRecipe,
-                                       VPTypeAnalysis &TypeInfo,
-                                       VPValue &AllOneMask, VPValue &EVL) {
-  // FIXME: Don't transform recipes to EVL recipes if they're not masked by the
-  // header mask.
-  auto GetNewMask = [&](VPValue *OrigMask) -> VPValue * {
-    assert(OrigMask && "Unmasked recipe when folding tail");
-    // HeaderMask will be handled using EVL.
-    VPValue *Mask;
-    if (match(OrigMask, m_LogicalAnd(m_Specific(HeaderMask), m_VPValue(Mask))))
-      return Mask;
-    return HeaderMask == OrigMask ? nullptr : OrigMask;
-  };
+                                       VPTypeAnalysis &TypeInfo, VPValue &EVL) {
+  VPlan *Plan = CurRecipe.getParent()->getPlan();
+  VPValue *Addr, *Mask, *EndPtr;
 
   /// Adjust any end pointers so that they point to the end of EVL lanes not VF.
-  auto GetNewAddr = [&CurRecipe, &EVL](VPValue *Addr) -> VPValue * {
-    auto *EndPtr = dyn_cast<VPVectorEndPointerRecipe>(Addr);
-    if (!EndPtr)
-      return Addr;
-    assert(EndPtr->getOperand(1) == &EndPtr->getParent()->getPlan()->getVF() &&
-           "VPVectorEndPointerRecipe with non-VF VF operand?");
-    assert(
-        all_of(EndPtr->users(),
-               [](VPUser *U) {
-                 return cast<VPWidenMemoryRecipe>(U)->isReverse();
-               }) &&
-        "VPVectorEndPointRecipe not used by reversed widened memory recipe?");
-    VPVectorEndPointerRecipe *EVLAddr = EndPtr->clone();
-    EVLAddr->insertBefore(&CurRecipe);
-    EVLAddr->setOperand(1, &EVL);
-    return EVLAddr;
+  auto AdjustEndPtr = [&CurRecipe, &EVL](VPValue *EndPtr) {
+    auto *EVLEndPtr = cast<VPVectorEndPointerRecipe>(EndPtr)->clone();
+    EVLEndPtr->insertBefore(&CurRecipe);
+    EVLEndPtr->setOperand(1, &EVL);
+    return EVLEndPtr;
   };
 
-  return TypeSwitch<VPRecipeBase *, VPRecipeBase *>(&CurRecipe)
-      .Case<VPWidenLoadRecipe>([&](VPWidenLoadRecipe *L) {
-        VPValue *NewMask = GetNewMask(L->getMask());
-        VPValue *NewAddr = GetNewAddr(L->getAddr());
-        return new VPWidenLoadEVLRecipe(*L, NewAddr, EVL, NewMask);
-      })
-      .Case<VPWidenStoreRecipe>([&](VPWidenStoreRecipe *S) {
-        VPValue *NewMask = GetNewMask(S->getMask());
-        VPValue *NewAddr = GetNewAddr(S->getAddr());
-        return new VPWidenStoreEVLRecipe(*S, NewAddr, EVL, NewMask);
-      })
-      .Case<VPInterleaveRecipe>([&](VPInterleaveRecipe *IR) {
-        VPValue *NewMask = GetNewMask(IR->getMask());
-        return new VPInterleaveEVLRecipe(*IR, EVL, NewMask);
-      })
-      .Case<VPReductionRecipe>([&](VPReductionRecipe *Red) {
-        VPValue *NewMask = GetNewMask(Red->getCondOp());
-        return new VPReductionEVLRecipe(*Red, EVL, NewMask);
-      })
-      .Case<VPInstruction>([&](VPInstruction *VPI) -> VPRecipeBase * {
-        VPValue *LHS, *RHS;
-        // Transform select with a header mask condition
-        //   select(header_mask, LHS, RHS)
-        // into vector predication merge.
-        //   vp.merge(all-true, LHS, RHS, EVL)
-        if (!match(VPI, m_Select(m_Specific(HeaderMask), m_VPValue(LHS),
-                                 m_VPValue(RHS))))
-          return nullptr;
-        // Use all true as the condition because this transformation is
-        // limited to selects whose condition is a header mask.
-        return new VPWidenIntrinsicRecipe(
-            Intrinsic::vp_merge, {&AllOneMask, LHS, RHS, &EVL},
-            TypeInfo.inferScalarType(LHS), VPI->getDebugLoc());
-      })
-      .Default([&](VPRecipeBase *R) { return nullptr; });
+  if (match(&CurRecipe,
+            m_MaskedLoad(m_VPValue(Addr), m_RemoveMask(HeaderMask, Mask))) &&
+      !cast<VPWidenLoadRecipe>(CurRecipe).isReverse())
+    return new VPWidenLoadEVLRecipe(cast<VPWidenLoadRecipe>(CurRecipe), Addr,
+                                    EVL, Mask);
+
+  if (match(&CurRecipe,
+            m_MaskedLoad(m_VPValue(EndPtr), m_RemoveMask(HeaderMask, Mask))) &&
+      match(EndPtr, m_VecEndPtr(m_VPValue(Addr), m_Specific(&Plan->getVF()))) &&
+      cast<VPWidenLoadRecipe>(CurRecipe).isReverse())
+    return new VPWidenLoadEVLRecipe(cast<VPWidenLoadRecipe>(CurRecipe),
+                                    AdjustEndPtr(EndPtr), EVL, Mask);
+
+  if (match(&CurRecipe, m_MaskedStore(m_VPValue(Addr), m_VPValue(),
+                                      m_RemoveMask(HeaderMask, Mask))) &&
+      !cast<VPWidenStoreRecipe>(CurRecipe).isReverse())
+    return new VPWidenStoreEVLRecipe(cast<VPWidenStoreRecipe>(CurRecipe), Addr,
+                                     EVL, Mask);
+
+  if (match(&CurRecipe, m_MaskedStore(m_VPValue(EndPtr), m_VPValue(),
+                                      m_RemoveMask(HeaderMask, Mask))) &&
+      match(EndPtr, m_VecEndPtr(m_VPValue(Addr), m_Specific(&Plan->getVF()))) &&
+      cast<VPWidenStoreRecipe>(CurRecipe).isReverse())
+    return new VPWidenStoreEVLRecipe(cast<VPWidenStoreRecipe>(CurRecipe),
+                                     AdjustEndPtr(EndPtr), EVL, Mask);
+
+  if (auto *Rdx = dyn_cast<VPReductionRecipe>(&CurRecipe))
+    if (Rdx->isConditional() &&
+        match(Rdx->getCondOp(), m_RemoveMask(HeaderMask, Mask)))
+      return new VPReductionEVLRecipe(*Rdx, EVL, Mask);
+
+  if (auto *Interleave = dyn_cast<VPInterleaveRecipe>(&CurRecipe))
+    if (Interleave->getMask() &&
+        match(Interleave->getMask(), m_RemoveMask(HeaderMask, Mask)))
+      return new VPInterleaveEVLRecipe(*Interleave, EVL, Mask);
+
+  VPValue *LHS, *RHS;
+  if (match(&CurRecipe,
+            m_Select(m_Specific(HeaderMask), m_VPValue(LHS), m_VPValue(RHS))))
+    return new VPWidenIntrinsicRecipe(
+        Intrinsic::vp_merge, {Plan->getTrue(), LHS, RHS, &EVL},
+        TypeInfo.inferScalarType(LHS), CurRecipe.getDebugLoc());
+
+  return nullptr;
 }
 
 /// Replace recipes with their EVL variants.
 static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
   VPTypeAnalysis TypeInfo(Plan);
-  VPValue *AllOneMask = Plan.getTrue();
   VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
   VPBasicBlock *Header = LoopRegion->getEntryBasicBlock();
 
@@ -2671,7 +2683,7 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
             ConstantInt::getSigned(Type::getInt32Ty(Plan.getContext()), -1));
         VPWidenIntrinsicRecipe *VPSplice = new VPWidenIntrinsicRecipe(
             Intrinsic::experimental_vp_splice,
-            {V1, V2, Imm, AllOneMask, PrevEVL, &EVL},
+            {V1, V2, Imm, Plan.getTrue(), PrevEVL, &EVL},
             TypeInfo.inferScalarType(R.getVPSingleValue()), R.getDebugLoc());
         VPSplice->insertBefore(&R);
         R.getVPSingleValue()->replaceAllUsesWith(VPSplice);
@@ -2705,7 +2717,7 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
   for (VPUser *U : collectUsersRecursively(EVLMask)) {
     auto *CurRecipe = cast<VPRecipeBase>(U);
     VPRecipeBase *EVLRecipe =
-        optimizeMaskToEVL(EVLMask, *CurRecipe, TypeInfo, *AllOneMask, EVL);
+        optimizeMaskToEVL(EVLMask, *CurRecipe, TypeInfo, EVL);
     if (!EVLRecipe)
       continue;