[LV] Provide utility routine to find uncounted exit recipes (#152530)

huntergr-arm · web-flow · commit 6b99a7bbed8d · 2025-09-18T15:45:23.000Z
Splitting out just the recipe finding code from #148626 into a utility function (along with the extra pattern matchers). Hopefully this makes reviewing a bit easier. Added a gtest, since this isn't actually used anywhere yet.
diff --git a/llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h b/llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h
@@ -356,6 +356,12 @@ m_BranchOnCount(const Op0_t &Op0, const Op1_t &Op1) {
   return m_VPInstruction<VPInstruction::BranchOnCount>(Op0, Op1);
 }
 
+template <typename Op0_t>
+inline VPInstruction_match<VPInstruction::AnyOf, Op0_t>
+m_AnyOf(const Op0_t &Op0) {
+  return m_VPInstruction<VPInstruction::AnyOf>(Op0);
+}
+
 template <unsigned Opcode, typename Op0_t>
 inline AllRecipe_match<Opcode, Op0_t> m_Unary(const Op0_t &Op0) {
   return AllRecipe_match<Opcode, Op0_t>(Op0);
@@ -714,6 +720,29 @@ m_Intrinsic(const T0 &Op0, const T1 &Op1, const T2 &Op2, const T3 &Op3) {
   return m_CombineAnd(m_Intrinsic<IntrID>(Op0, Op1, Op2), m_Argument<3>(Op3));
 }
 
+struct live_in_vpvalue {
+  template <typename ITy> bool match(ITy *V) const {
+    VPValue *Val = dyn_cast<VPValue>(V);
+    return Val && Val->isLiveIn();
+  }
+};
+
+inline live_in_vpvalue m_LiveIn() { return live_in_vpvalue(); }
+
+template <typename SubPattern_t> struct OneUse_match {
+  SubPattern_t SubPattern;
+
+  OneUse_match(const SubPattern_t &SP) : SubPattern(SP) {}
+
+  template <typename OpTy> bool match(OpTy *V) {
+    return V->hasOneUse() && SubPattern.match(V);
+  }
+};
+
+template <typename T> inline OneUse_match<T> m_OneUse(const T &SubPattern) {
+  return SubPattern;
+}
+
 } // namespace VPlanPatternMatch
 } // namespace llvm
 
diff --git a/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp b/llvm/lib/Transforms/Vectorize/VPlanUtils.cpp
@@ -140,3 +140,101 @@ VPBasicBlock *vputils::getFirstLoopHeader(VPlan &Plan, VPDominatorTree &VPDT) {
   });
   return I == DepthFirst.end() ? nullptr : cast<VPBasicBlock>(*I);
 }
+
+std::optional<VPValue *>
+vputils::getRecipesForUncountableExit(VPlan &Plan,
+                                      SmallVectorImpl<VPRecipeBase *> &Recipes,
+                                      SmallVectorImpl<VPRecipeBase *> &GEPs) {
+  using namespace llvm::VPlanPatternMatch;
+  // Given a VPlan like the following (just including the recipes contributing
+  // to loop control exiting here, not the actual work), we're looking to match
+  // the recipes contributing to the uncountable exit condition comparison
+  // (here, vp<%4>) back to either live-ins or the address nodes for the load
+  // used as part of the uncountable exit comparison so that we can copy them
+  // to a preheader and rotate the address in the loop to the next vector
+  // iteration.
+  //
+  // Currently, the address of the load is restricted to a GEP with 2 operands
+  // and a live-in base address. This constraint may be relaxed later.
+  //
+  // VPlan ' for UF>=1' {
+  // Live-in vp<%0> = VF
+  // Live-in ir<64> = original trip-count
+  //
+  // entry:
+  // Successor(s): preheader, vector.ph
+  //
+  // vector.ph:
+  // Successor(s): vector loop
+  //
+  // <x1> vector loop: {
+  //   vector.body:
+  //     EMIT vp<%2> = CANONICAL-INDUCTION ir<0>
+  //     vp<%3> = SCALAR-STEPS vp<%2>, ir<1>, vp<%0>
+  //     CLONE ir<%ee.addr> = getelementptr ir<0>, vp<%3>
+  //     WIDEN ir<%ee.load> = load ir<%ee.addr>
+  //     WIDEN vp<%4> = icmp eq ir<%ee.load>, ir<0>
+  //     EMIT vp<%5> = any-of vp<%4>
+  //     EMIT vp<%6> = add vp<%2>, vp<%0>
+  //     EMIT vp<%7> = icmp eq vp<%6>, ir<64>
+  //     EMIT vp<%8> = or vp<%5>, vp<%7>
+  //     EMIT branch-on-cond vp<%8>
+  //   No successors
+  // }
+  // Successor(s): middle.block
+  //
+  // middle.block:
+  // Successor(s): preheader
+  //
+  // preheader:
+  // No successors
+  // }
+
+  // Find the uncountable loop exit condition.
+  auto *Region = Plan.getVectorLoopRegion();
+  VPValue *UncountableCondition = nullptr;
+  if (!match(Region->getExitingBasicBlock()->getTerminator(),
+             m_BranchOnCond(m_OneUse(m_c_BinaryOr(
+                 m_AnyOf(m_VPValue(UncountableCondition)), m_VPValue())))))
+    return std::nullopt;
+
+  SmallVector<VPValue *, 4> Worklist;
+  Worklist.push_back(UncountableCondition);
+  while (!Worklist.empty()) {
+    VPValue *V = Worklist.pop_back_val();
+
+    // Any value defined outside the loop does not need to be copied.
+    if (V->isDefinedOutsideLoopRegions())
+      continue;
+
+    // FIXME: Remove the single user restriction; it's here because we're
+    //        starting with the simplest set of loops we can, and multiple
+    //        users means needing to add PHI nodes in the transform.
+    if (V->getNumUsers() > 1)
+      return std::nullopt;
+
+    VPValue *Op1, *Op2;
+    // Walk back through recipes until we find at least one load from memory.
+    if (match(V, m_ICmp(m_VPValue(Op1), m_VPValue(Op2)))) {
+      Worklist.push_back(Op1);
+      Worklist.push_back(Op2);
+      Recipes.push_back(V->getDefiningRecipe());
+    } else if (auto *Load = dyn_cast<VPWidenLoadRecipe>(V)) {
+      // Reject masked loads for the time being; they make the exit condition
+      // more complex.
+      if (Load->isMasked())
+        return std::nullopt;
+
+      VPValue *GEP = Load->getAddr();
+      if (!match(GEP, m_GetElementPtr(m_LiveIn(), m_VPValue())))
+        return std::nullopt;
+
+      Recipes.push_back(Load);
+      Recipes.push_back(GEP->getDefiningRecipe());
+      GEPs.push_back(GEP->getDefiningRecipe());
+    } else
+      return std::nullopt;
+  }
+
+  return UncountableCondition;
+}
diff --git a/llvm/lib/Transforms/Vectorize/VPlanUtils.h b/llvm/lib/Transforms/Vectorize/VPlanUtils.h
@@ -101,6 +101,17 @@ bool isUniformAcrossVFsAndUFs(VPValue *V);
 /// Returns the header block of the first, top-level loop, or null if none
 /// exist.
 VPBasicBlock *getFirstLoopHeader(VPlan &Plan, VPDominatorTree &VPDT);
+
+/// Returns the VPValue representing the uncountable exit comparison used by
+/// AnyOf if the recipes it depends on can be traced back to live-ins and
+/// the addresses (in GEP/PtrAdd form) of any (non-masked) load used in
+/// generating the values for the comparison. The recipes are stored in
+/// \p Recipes, and recipes forming an address for a load are also added to
+/// \p GEPs.
+std::optional<VPValue *>
+getRecipesForUncountableExit(VPlan &Plan,
+                             SmallVectorImpl<VPRecipeBase *> &Recipes,
+                             SmallVectorImpl<VPRecipeBase *> &GEPs);
 } // namespace vputils
 
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/Transforms/Vectorize/VPlanValue.h b/llvm/lib/Transforms/Vectorize/VPlanValue.h
@@ -148,6 +148,8 @@ class LLVM_ABI_FOR_TEST VPValue {
     return Current != user_end();
   }
 
+  bool hasOneUse() const { return getNumUsers() == 1; }
+
   void replaceAllUsesWith(VPValue *New);
 
   /// Go through the uses list for this VPValue and make each use point to \p
diff --git a/llvm/unittests/Transforms/Vectorize/CMakeLists.txt b/llvm/unittests/Transforms/Vectorize/CMakeLists.txt
@@ -14,5 +14,6 @@ add_llvm_unittest(VectorizeTests
   VPlanHCFGTest.cpp
   VPlanPatternMatchTest.cpp
   VPlanSlpTest.cpp
+  VPlanUncountableExitTest.cpp
   VPlanVerifierTest.cpp
   )
diff --git a/llvm/unittests/Transforms/Vectorize/VPlanTestBase.h b/llvm/unittests/Transforms/Vectorize/VPlanTestBase.h
@@ -65,7 +65,7 @@ class VPlanTestIRBase : public testing::Test {
   }
 
   /// Build the VPlan for the loop starting from \p LoopHeader.
-  VPlanPtr buildVPlan(BasicBlock *LoopHeader) {
+  VPlanPtr buildVPlan(BasicBlock *LoopHeader, bool HasUncountableExit = false) {
     Function &F = *LoopHeader->getParent();
     assert(!verifyFunction(F) && "input function must be valid");
     doAnalysis(F);
@@ -75,7 +75,7 @@ class VPlanTestIRBase : public testing::Test {
     auto Plan = VPlanTransforms::buildVPlan0(L, *LI, IntegerType::get(*Ctx, 64),
                                              {}, PSE);
 
-    VPlanTransforms::handleEarlyExits(*Plan, false);
+    VPlanTransforms::handleEarlyExits(*Plan, HasUncountableExit);
     VPlanTransforms::addMiddleCheck(*Plan, true, false);
 
     VPlanTransforms::createLoopRegions(*Plan);
diff --git a/llvm/unittests/Transforms/Vectorize/VPlanUncountableExitTest.cpp b/llvm/unittests/Transforms/Vectorize/VPlanUncountableExitTest.cpp
@@ -0,0 +1,102 @@
+//===- llvm/unittests/Transforms/Vectorize/VPlanUncountableExitTest.cpp ---===//
+//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "../lib/Transforms/Vectorize/VPlan.h"
+#include "../lib/Transforms/Vectorize/VPlanUtils.h"
+#include "VPlanTestBase.h"
+#include "llvm/ADT/SmallVector.h"
+#include "gtest/gtest.h"
+
+namespace llvm {
+
+namespace {
+class VPUncountableExitTest : public VPlanTestIRBase {};
+
+TEST_F(VPUncountableExitTest, FindUncountableExitRecipes) {
+  const char *ModuleString =
+      "define void @f(ptr %array, ptr %pred) {\n"
+      "entry:\n"
+      "  br label %for.body\n"
+      "for.body:\n"
+      "  %iv = phi i64 [ 0, %entry ], [ %iv.next, %for.inc ]\n"
+      "  %st.addr = getelementptr inbounds i16, ptr %array, i64 %iv\n"
+      "  %data = load i16, ptr %st.addr, align 2\n"
+      "  %inc = add nsw i16 %data, 1\n"
+      "  store i16 %inc, ptr %st.addr, align 2\n"
+      "  %uncountable.addr = getelementptr inbounds nuw i16, ptr %pred, i64 "
+      "%iv\n"
+      "  %uncountable.val = load i16, ptr %uncountable.addr, align 2\n"
+      "  %uncountable.cond = icmp sgt i16 %uncountable.val, 500\n"
+      "  br i1 %uncountable.cond, label %exit, label %for.inc\n"
+      "for.inc:\n"
+      "  %iv.next = add nuw nsw i64 %iv, 1\n"
+      "  %countable.cond = icmp eq i64 %iv.next, 20\n"
+      " br i1 %countable.cond, label %exit, label %for.body\n"
+      "exit:\n"
+      "  ret void\n"
+      "}\n";
+
+  Module &M = parseModule(ModuleString);
+
+  Function *F = M.getFunction("f");
+  BasicBlock *LoopHeader = F->getEntryBlock().getSingleSuccessor();
+  auto Plan = buildVPlan(LoopHeader, /*HasUncountableExit=*/true);
+  VPlanTransforms::tryToConvertVPInstructionsToVPRecipes(
+      Plan, [](PHINode *P) { return nullptr; }, *TLI);
+  VPlanTransforms::runPass(VPlanTransforms::optimize, *Plan);
+
+  SmallVector<VPRecipeBase *> Recipes;
+  SmallVector<VPRecipeBase *> GEPs;
+
+  std::optional<VPValue *> UncountableCondition =
+      vputils::getRecipesForUncountableExit(*Plan, Recipes, GEPs);
+  ASSERT_TRUE(UncountableCondition.has_value());
+  ASSERT_EQ(GEPs.size(), 1ull);
+  ASSERT_EQ(Recipes.size(), 3ull);
+}
+
+TEST_F(VPUncountableExitTest, NoUncountableExit) {
+  const char *ModuleString =
+      "define void @f(ptr %array, ptr %pred) {\n"
+      "entry:\n"
+      "  br label %for.body\n"
+      "for.body:\n"
+      "  %iv = phi i64 [ 0, %entry ], [ %iv.next, %for.body ]\n"
+      "  %st.addr = getelementptr inbounds i16, ptr %array, i64 %iv\n"
+      "  %data = load i16, ptr %st.addr, align 2\n"
+      "  %inc = add nsw i16 %data, 1\n"
+      "  store i16 %inc, ptr %st.addr, align 2\n"
+      "  %iv.next = add nuw nsw i64 %iv, 1\n"
+      "  %countable.cond = icmp eq i64 %iv.next, 20\n"
+      " br i1 %countable.cond, label %exit, label %for.body\n"
+      "exit:\n"
+      "  ret void\n"
+      "}\n";
+
+  Module &M = parseModule(ModuleString);
+
+  Function *F = M.getFunction("f");
+  BasicBlock *LoopHeader = F->getEntryBlock().getSingleSuccessor();
+  auto Plan = buildVPlan(LoopHeader);
+  VPlanTransforms::tryToConvertVPInstructionsToVPRecipes(
+      Plan, [](PHINode *P) { return nullptr; }, *TLI);
+  VPlanTransforms::runPass(VPlanTransforms::optimize, *Plan);
+
+  SmallVector<VPRecipeBase *> Recipes;
+  SmallVector<VPRecipeBase *> GEPs;
+
+  std::optional<VPValue *> UncountableCondition =
+      vputils::getRecipesForUncountableExit(*Plan, Recipes, GEPs);
+  ASSERT_FALSE(UncountableCondition.has_value());
+  ASSERT_EQ(GEPs.size(), 0ull);
+  ASSERT_EQ(Recipes.size(), 0ull);
+}
+
+} // namespace
+} // namespace llvm

Original file line number	Diff line number	Diff line change
`@@ -148,6 +148,8 @@ class LLVM_ABI_FOR_TEST VPValue {`
`148`	`148`	`return Current != user_end();`
`149`	`149`	`}`
`150`	`150`
	`151`	`+ bool hasOneUse() const { return getNumUsers() == 1; }`
	`152`	`+`
`151`	`153`	`void replaceAllUsesWith(VPValue *New);`
`152`	`154`
`153`	`155`	`/// Go through the uses list for this VPValue and make each use point to \p`
Original file line number	Diff line number	Diff line change
`@@ -14,5 +14,6 @@ add_llvm_unittest(VectorizeTests`
`14`	`14`	`VPlanHCFGTest.cpp`
`15`	`15`	`VPlanPatternMatchTest.cpp`
`16`	`16`	`VPlanSlpTest.cpp`
	`17`	`+ VPlanUncountableExitTest.cpp`
`17`	`18`	`VPlanVerifierTest.cpp`
`18`	`19`	`)`