[BasicAA] Treat different VScale intrinsics as the same value. (#81152)

The IR may contain multiple llvm.vscale intrinsics that have not been CSEd.
This patch ensures that multiple vscales can be treated the same, either in the
decomposition of geps and when we subtract one decomposition from another.

Author: davemgreen

llvm/lib/Analysis/BasicAliasAnalysis.cpp

@@ -188,6 +188,12 @@ static bool isObjectSize(const Value *V, TypeSize Size, const DataLayout &DL,
   return ObjectSize && *ObjectSize == Size;
 }
 
+/// Return true if both V1 and V2 are VScale
+static bool areBothVScale(const Value *V1, const Value *V2) {
+  return PatternMatch::match(V1, PatternMatch::m_VScale()) &&
+         PatternMatch::match(V2, PatternMatch::m_VScale());
+}
+
 //===----------------------------------------------------------------------===//
 // CaptureInfo implementations
 //===----------------------------------------------------------------------===//
@@ -679,7 +685,8 @@ BasicAAResult::DecomposeGEPExpression(const Value *V, const DataLayout &DL,
       //   A[x][x] -> x*16 + x*4 -> x*20
       // This also ensures that 'x' only appears in the index list once.
       for (unsigned i = 0, e = Decomposed.VarIndices.size(); i != e; ++i) {
-        if (Decomposed.VarIndices[i].Val.V == LE.Val.V &&
+        if ((Decomposed.VarIndices[i].Val.V == LE.Val.V ||
+             areBothVScale(Decomposed.VarIndices[i].Val.V, LE.Val.V)) &&
             Decomposed.VarIndices[i].Val.hasSameCastsAs(LE.Val)) {
           Scale += Decomposed.VarIndices[i].Scale;
           LE.IsNSW = false; // We cannot guarantee nsw for the merge.
@@ -1792,7 +1799,8 @@ void BasicAAResult::subtractDecomposedGEPs(DecomposedGEP &DestGEP,
     bool Found = false;
     for (auto I : enumerate(DestGEP.VarIndices)) {
       VariableGEPIndex &Dest = I.value();
-      if (!isValueEqualInPotentialCycles(Dest.Val.V, Src.Val.V, AAQI) ||
+      if ((!isValueEqualInPotentialCycles(Dest.Val.V, Src.Val.V, AAQI) &&
+           !areBothVScale(Dest.Val.V, Src.Val.V)) ||
           !Dest.Val.hasSameCastsAs(Src.Val))
         continue;
 

llvm/test/Analysis/BasicAA/vscale.ll

@@ -488,9 +488,9 @@ define void @onevscale(ptr %p) vscale_range(1,16) {
 }
 
 ; CHECK-LABEL: twovscales
-; CHECK-DAG:   MayAlias:     <vscale x 4 x i32>* %vp161, <vscale x 4 x i32>* %vp162
+; CHECK-DAG:   MustAlias:    <vscale x 4 x i32>* %vp161, <vscale x 4 x i32>* %vp162
 ; CHECK-DAG:   NoAlias:      <vscale x 4 x i32>* %vp161, <vscale x 4 x i32>* %vp161b
-; CHECK-DAG:   MayAlias:     <vscale x 4 x i32>* %vp161b, <vscale x 4 x i32>* %vp162
+; CHECK-DAG:   NoAlias:      <vscale x 4 x i32>* %vp161b, <vscale x 4 x i32>* %vp162
 define void @twovscales(ptr %p) vscale_range(1,16) {
   %v1 = call i64 @llvm.vscale.i64()
   %v2 = call i64 @llvm.vscale.i64()