[llvm] 5e6b4be - [BasicAA] Treat different VScale intrinsics as the same value. (#81152)

[via llvm-commits]

Author: David Green
Date: 2024-02-12T11:27:49Z
New Revision: 5e6b4be5cbddbc7538cdae0f0889b116e386fcca

URL: https://github.com/llvm/llvm-project/commit/5e6b4be5cbddbc7538cdae0f0889b116e386fcca
DIFF: https://github.com/llvm/llvm-project/commit/5e6b4be5cbddbc7538cdae0f0889b116e386fcca.diff

LOG: [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.

Added: 
    

Modified: 
    llvm/lib/Analysis/BasicAliasAnalysis.cpp
    llvm/test/Analysis/BasicAA/vscale.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 2ea29177a5cf0f..8dfc4b2a1cb1f4 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/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;
 

diff  --git a/llvm/test/Analysis/BasicAA/vscale.ll b/llvm/test/Analysis/BasicAA/vscale.ll
index 18aad4ffe73f49..05b9b6b3c3a970 100644
--- a/llvm/test/Analysis/BasicAA/vscale.ll
+++ b/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()