[llvm] [LAA] Consider accessed addrspace when mapping underlying obj to access. (PR #129087)

[Florian Hahn via llvm-commits]

https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/129087

In some cases, it is possible for the same underlying object to be accessed via pointers to different address spaces. This could lead to pointers from different address spaces ending up in the same dependency set, which isn't allowed (and triggers an assertion).

Update the mapping from underlying object -> last access to also include the accessing address space.

Fixes https://github.com/llvm/llvm-project/issues/124759.

>From 3a00d3993e04249a55f3f21bd036d363ceb72717 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Thu, 27 Feb 2025 16:57:14 +0000
Subject: [PATCH] [LAA] Consider accessed addrspace when mapping underlying obj
 to access.

In some cases, it is possible for the same underlying object to be
accessed via pointers to different address spaces. This could lead to
pointers from different address spaces ending up in the same dependency
set, which isn't allowed (and triggers an assertion).

Update the mapping from underlying object -> last access to also include
the accessing address space.

Fixes https://github.com/llvm/llvm-project/issues/124759.
---
 llvm/lib/Analysis/LoopAccessAnalysis.cpp      | 12 ++++--
 ...erlying-object-different-address-spaces.ll | 39 +++++++++++++++++++
 2 files changed, 47 insertions(+), 4 deletions(-)
 create mode 100644 llvm/test/Analysis/LoopAccessAnalysis/underlying-object-different-address-spaces.ll

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index cf3bb6a8eae1c..38ee82b77a946 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1362,8 +1362,10 @@ void AccessAnalysis::processMemAccesses() {
 
     bool SetHasWrite = false;
 
-    // Map of pointers to last access encountered.
-    typedef DenseMap<const Value*, MemAccessInfo> UnderlyingObjToAccessMap;
+    // Map of (pointer to underlying objects, accessed address space) to last
+    // access encountered.
+    typedef DenseMap<std::pair<const Value *, unsigned>, MemAccessInfo>
+        UnderlyingObjToAccessMap;
     UnderlyingObjToAccessMap ObjToLastAccess;
 
     // Set of access to check after all writes have been processed.
@@ -1443,8 +1445,10 @@ void AccessAnalysis::processMemAccesses() {
                     UnderlyingObj->getType()->getPointerAddressSpace()))
               continue;
 
-            auto [It, Inserted] =
-                ObjToLastAccess.try_emplace(UnderlyingObj, Access);
+            auto [It, Inserted] = ObjToLastAccess.try_emplace(
+                {UnderlyingObj,
+                 cast<PointerType>(Ptr->getType())->getAddressSpace()},
+                Access);
             if (!Inserted) {
               DepCands.unionSets(Access, It->second);
               It->second = Access;
diff --git a/llvm/test/Analysis/LoopAccessAnalysis/underlying-object-different-address-spaces.ll b/llvm/test/Analysis/LoopAccessAnalysis/underlying-object-different-address-spaces.ll
new file mode 100644
index 0000000000000..adf73c091be00
--- /dev/null
+++ b/llvm/test/Analysis/LoopAccessAnalysis/underlying-object-different-address-spaces.ll
@@ -0,0 +1,39 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes='print<access-info>' -disable-output %s 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+
+; Test case for https://github.com/llvm/llvm-project/issues/124759. The same
+; underlying object is access through pointers with different address spaces.
+define void @same_underlying_object_different_address_spaces(ptr %dst1.as1, ptr %dst2.as1) {
+; CHECK-LABEL: 'same_underlying_object_different_address_spaces'
+; CHECK-NEXT:    loop:
+; CHECK-NEXT:      Report: cannot identify array bounds
+; CHECK-NEXT:      Dependences:
+; CHECK-NEXT:      Run-time memory checks:
+; CHECK-NEXT:      Grouped accesses:
+; CHECK-EMPTY:
+; CHECK-NEXT:      Non vectorizable stores to invariant address were not found in loop.
+; CHECK-NEXT:      SCEV assumptions:
+; CHECK-EMPTY:
+; CHECK-NEXT:      Expressions re-written:
+;
+entry:
+  %alloc = alloca i8, i64 0, align 128
+  %as3 = addrspacecast ptr %alloc to ptr addrspace(3)
+  %as4 = addrspacecast ptr %alloc to ptr addrspace(4)
+  br label %loop
+
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  store i32 0, ptr addrspace(4) %as4, align 4
+  store i32 0, ptr %dst1.as1, align 4
+  %l = load i64, ptr addrspace(3) %as3, align 4
+  store i64 %l, ptr %dst2.as1, align 4
+  %iv.next = add i64 %iv, 1
+  %c = icmp eq i64 %iv.next, 100
+  br i1 %c, label %loop, label %exit
+
+exit:
+  ret void
+}