[LV] Fix ScalarIVSteps vplan pattern matcher, remove m_CanonicalIV() (#138298)

783a846 changed VPScalarIVStepsRecipe to take 3 arguments (adding
VF explicitly) instead of 2, but didn't change the corresponding
pattern matcher.

This matcher was only used in vputils::isHeaderMask, and no test
ever reached that function with a ScalarIVSteps recipe for the
value being matched -- it was always a WideCanonicalIV. So the
matcher bailed out immediately before checking arguments and
asserting that the number of arguments in the recipe was the
same provided by the matcher.

Since the constructors for ScalarIVSteps take 3 values, we should
be safe to update the matcher and guard it with a dedicated gtest.

m_CanonicalIV() on the other hand is removed; as a phi recipe it
may not have a consistent number of arguments to match, only
requiring one (the start value) when being constructed with the
assumption that a second incoming value is added for the backedge
later. In order to keep the matcher we would need to add multiple
matchers with different numbers of arguments for it depending on
what phase of vplan construction we were in, and ensure that we
never reorder matcher usage vs. vplan transformation. Since the
main IR PatternMatch.h doesn't contain any matchers for PHI nodes,
I think we can just remove it and match via m_Specific() using the
VPValue we get from Plan.getCanonicalIV().

Author: huntergr-arm

llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h

@@ -461,21 +461,14 @@ m_LogicalOr(const Op0_t &Op0, const Op1_t &Op1) {
   return m_Select(Op0, m_True(), Op1);
 }
 
-using VPCanonicalIVPHI_match =
-    Recipe_match<std::tuple<>, 0, false, VPCanonicalIVPHIRecipe>;
-
-inline VPCanonicalIVPHI_match m_CanonicalIV() {
-  return VPCanonicalIVPHI_match();
-}
-
-template <typename Op0_t, typename Op1_t>
+template <typename Op0_t, typename Op1_t, typename Op2_t>
 using VPScalarIVSteps_match =
-    Recipe_match<std::tuple<Op0_t, Op1_t>, 0, false, VPScalarIVStepsRecipe>;
+    TernaryRecipe_match<Op0_t, Op1_t, Op2_t, 0, false, VPScalarIVStepsRecipe>;
 
-template <typename Op0_t, typename Op1_t>
-inline VPScalarIVSteps_match<Op0_t, Op1_t> m_ScalarIVSteps(const Op0_t &Op0,
-                                                           const Op1_t &Op1) {
-  return VPScalarIVSteps_match<Op0_t, Op1_t>(Op0, Op1);
+template <typename Op0_t, typename Op1_t, typename Op2_t>
+inline VPScalarIVSteps_match<Op0_t, Op1_t, Op2_t>
+m_ScalarIVSteps(const Op0_t &Op0, const Op1_t &Op1, const Op2_t &Op2) {
+  return VPScalarIVSteps_match<Op0_t, Op1_t, Op2_t>({Op0, Op1, Op2});
 }
 
 template <typename Op0_t, typename Op1_t, typename Op2_t>

llvm/lib/Transforms/Vectorize/VPlanUtils.cpp

@@ -62,7 +62,9 @@ bool vputils::isHeaderMask(const VPValue *V, VPlan &Plan) {
 
   if (match(V, m_ActiveLaneMask(m_VPValue(A), m_VPValue(B))))
     return B == Plan.getTripCount() &&
-           (match(A, m_ScalarIVSteps(m_CanonicalIV(), m_SpecificInt(1))) ||
+           (match(A, m_ScalarIVSteps(m_Specific(Plan.getCanonicalIV()),
+                                     m_SpecificInt(1),
+                                     m_Specific(&Plan.getVF()))) ||
             IsWideCanonicalIV(A));
 
   return match(V, m_Binary<Instruction::ICmp>(m_VPValue(A), m_VPValue(B))) &&

llvm/unittests/Transforms/Vectorize/CMakeLists.txt

@@ -12,6 +12,7 @@ add_llvm_unittest(VectorizeTests
   VPlanTest.cpp
   VPDomTreeTest.cpp
   VPlanHCFGTest.cpp
+  VPlanPatternMatchTest.cpp
   VPlanSlpTest.cpp
   VPlanVerifierTest.cpp
   )

llvm/unittests/Transforms/Vectorize/VPlanPatternMatchTest.cpp

@@ -0,0 +1,55 @@
+//===- llvm/unittests/Transforms/Vectorize/VPlanPatternMatchTest.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/VPlanPatternMatch.h"
+#include "../lib/Transforms/Vectorize/LoopVectorizationPlanner.h"
+#include "../lib/Transforms/Vectorize/VPlan.h"
+#include "../lib/Transforms/Vectorize/VPlanHelpers.h"
+#include "VPlanTestBase.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "gtest/gtest.h"
+
+namespace llvm {
+
+namespace {
+using VPPatternMatchTest = VPlanTestBase;
+
+TEST_F(VPPatternMatchTest, ScalarIVSteps) {
+  VPlan &Plan = getPlan();
+  VPBasicBlock *VPBB = Plan.createVPBasicBlock("");
+  VPBuilder Builder(VPBB);
+
+  IntegerType *I64Ty = IntegerType::get(C, 64);
+  VPValue *StartV = Plan.getOrAddLiveIn(ConstantInt::get(I64Ty, 0));
+  auto *CanonicalIVPHI = new VPCanonicalIVPHIRecipe(StartV, DebugLoc());
+  Builder.insert(CanonicalIVPHI);
+
+  VPValue *Inc = Plan.getOrAddLiveIn(ConstantInt::get(I64Ty, 1));
+  VPValue *VF = &Plan.getVF();
+  VPValue *Steps = Builder.createScalarIVSteps(
+      Instruction::Add, nullptr, CanonicalIVPHI, Inc, VF, DebugLoc());
+
+  VPValue *Inc2 = Plan.getOrAddLiveIn(ConstantInt::get(I64Ty, 2));
+  VPValue *Steps2 = Builder.createScalarIVSteps(
+      Instruction::Add, nullptr, CanonicalIVPHI, Inc2, VF, DebugLoc());
+
+  using namespace VPlanPatternMatch;
+
+  ASSERT_TRUE(match(Steps, m_ScalarIVSteps(m_Specific(CanonicalIVPHI),
+                                           m_SpecificInt(1), m_Specific(VF))));
+  ASSERT_FALSE(
+      match(Steps2, m_ScalarIVSteps(m_Specific(CanonicalIVPHI),
+                                    m_SpecificInt(1), m_Specific(VF))));
+  ASSERT_TRUE(match(Steps2, m_ScalarIVSteps(m_Specific(CanonicalIVPHI),
+                                            m_SpecificInt(2), m_Specific(VF))));
+}
+
+} // namespace
+} // namespace llvm