[llvm] [LLVM][PatternMatch] Simplify m_VScale to only match against llvm.vscale(). (PR #142773)

[Paul Walker via llvm-commits]

https://github.com/paulwalker-arm created https://github.com/llvm/llvm-project/pull/142773

The getelementptr based representation of vscale only existed to allow a constant representation of vscale, which has long since been removed.

Whilst it's possible for m_VScale to match against the non-constant sequence, this is not a desirable representation when compared to using llvm.vscale(), which is born out from there being no IR tests.

>From 67710923fb8ae3569160c844bd6476ff0fca7c06 Mon Sep 17 00:00:00 2001
From: Paul Walker <paul.walker at arm.com>
Date: Wed, 4 Jun 2025 12:09:55 +0000
Subject: [PATCH] [LLVM][PatternMatch] Simplify m_VScale to only match against
 llvm.vscale().

The getelementptr based representation of vscale only existed to
allow a constant representation of vscale, which has long since been
removed.

Whilst it's possible for m_VScale to match against the non-constant
sequence, this is not a desirable representation when compared to
using llvm.vscale(), which is born out from there being no IR tests.
---
 llvm/include/llvm/IR/PatternMatch.h | 31 +++--------------------------
 llvm/unittests/IR/PatternMatch.cpp  | 19 ------------------
 2 files changed, 3 insertions(+), 47 deletions(-)

diff --git a/llvm/include/llvm/IR/PatternMatch.h b/llvm/include/llvm/IR/PatternMatch.h
index 6242a686e7bc0..a00d0813fab1b 100644
--- a/llvm/include/llvm/IR/PatternMatch.h
+++ b/llvm/include/llvm/IR/PatternMatch.h
@@ -3046,34 +3046,9 @@ inline InsertValue_match<Ind, Val_t, Elt_t> m_InsertValue(const Val_t &Val,
   return InsertValue_match<Ind, Val_t, Elt_t>(Val, Elt);
 }
 
-/// Matches patterns for `vscale`. This can either be a call to `llvm.vscale` or
-/// the constant expression
-///  `ptrtoint(gep <vscale x 1 x i8>, <vscale x 1 x i8>* null, i32 1>`
-/// under the right conditions determined by DataLayout.
-struct VScaleVal_match {
-  template <typename ITy> bool match(ITy *V) const {
-    if (m_Intrinsic<Intrinsic::vscale>().match(V))
-      return true;
-
-    Value *Ptr;
-    if (m_PtrToInt(m_Value(Ptr)).match(V)) {
-      if (auto *GEP = dyn_cast<GEPOperator>(Ptr)) {
-        auto *DerefTy =
-            dyn_cast<ScalableVectorType>(GEP->getSourceElementType());
-        if (GEP->getNumIndices() == 1 && DerefTy &&
-            DerefTy->getElementType()->isIntegerTy(8) &&
-            m_Zero().match(GEP->getPointerOperand()) &&
-            m_SpecificInt(1).match(GEP->idx_begin()->get()))
-          return true;
-      }
-    }
-
-    return false;
-  }
-};
-
-inline VScaleVal_match m_VScale() {
-  return VScaleVal_match();
+/// Matches a call to `llvm.vscale()`.
+inline IntrinsicID_match m_VScale() {
+  return m_Intrinsic<Intrinsic::vscale>();
 }
 
 template <typename Opnd0, typename Opnd1>
diff --git a/llvm/unittests/IR/PatternMatch.cpp b/llvm/unittests/IR/PatternMatch.cpp
index 7b3a4ce365453..bb7cc0802b1df 100644
--- a/llvm/unittests/IR/PatternMatch.cpp
+++ b/llvm/unittests/IR/PatternMatch.cpp
@@ -2355,25 +2355,6 @@ TEST_F(PatternMatchTest, VectorLogicalSelects) {
   EXPECT_FALSE(match(MixedTypeOr, m_LogicalOr(m_Value(), m_Value())));
 }
 
-TEST_F(PatternMatchTest, VScale) {
-  DataLayout DL = M->getDataLayout();
-
-  Type *VecTy = ScalableVectorType::get(IRB.getInt8Ty(), 1);
-  Value *NullPtrVec =
-      Constant::getNullValue(PointerType::getUnqual(VecTy->getContext()));
-  Value *GEP = IRB.CreateGEP(VecTy, NullPtrVec, IRB.getInt64(1));
-  Value *PtrToInt = IRB.CreatePtrToInt(GEP, DL.getIntPtrType(GEP->getType()));
-  EXPECT_TRUE(match(PtrToInt, m_VScale()));
-
-  Type *VecTy2 = ScalableVectorType::get(IRB.getInt8Ty(), 2);
-  Value *NullPtrVec2 =
-      Constant::getNullValue(PointerType::getUnqual(VecTy2->getContext()));
-  Value *GEP2 = IRB.CreateGEP(VecTy, NullPtrVec2, IRB.getInt64(1));
-  Value *PtrToInt2 =
-      IRB.CreatePtrToInt(GEP2, DL.getIntPtrType(GEP2->getType()));
-  EXPECT_TRUE(match(PtrToInt2, m_VScale()));
-}
-
 TEST_F(PatternMatchTest, NotForbidPoison) {
   Type *ScalarTy = IRB.getInt8Ty();
   Type *VectorTy = FixedVectorType::get(ScalarTy, 3);