[PATCH] D127202: [InlineFunction] Handle early exit during getUnderlyingObjects due to MaxLookup

[Ting Wang via Phabricator via llvm-commits]

tingwang updated this revision to Diff 436272.
tingwang retitled this revision from "[InlineFunction] Call to getUnderlyingObjects inside AddAliasScopeMetadata shall set MaxLookup = 0" to "[InlineFunction] Handle early exit during getUnderlyingObjects due to MaxLookup".
tingwang edited the summary of this revision.
tingwang added a comment.

(1) Conditionally detect early exit during getUnderlyingObjects by invoke getUnderlyingObjects a second time. If we got new pointers, then the first walk had trouble, and be conservative in this case.
(2) Updated using nikic's simple test case.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D127202/new/

https://reviews.llvm.org/D127202

Files:
  llvm/lib/Transforms/Utils/InlineFunction.cpp
  llvm/test/Transforms/Inline/inline-noalias.ll


Index: llvm/test/Transforms/Inline/inline-noalias.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/Inline/inline-noalias.ll
@@ -0,0 +1,23 @@
+; RUN: opt < %s -passes=inline -S | FileCheck %s
+
+define i32 @caller(ptr %p) {
+  %v = call i32 @callee(ptr %p)
+    ret i32 %v
+}
+
+define internal i32 @callee(ptr noalias %p) {
+  %p.8 = getelementptr i8, ptr %p, i64 8
+; CHECK: %v.i = load i32, ptr %p.8.i, align 4, !alias.scope ![[ALIAS0:[0-9]+]]
+  %v = load i32, ptr %p.8
+  %p.1 = getelementptr i8, ptr %p, i64 1
+  %p.2 = getelementptr i8, ptr %p.1, i64 1
+  %p.3 = getelementptr i8, ptr %p.2, i64 1
+  %p.4 = getelementptr i8, ptr %p.3, i64 1
+  %p.5 = getelementptr i8, ptr %p.4, i64 1
+  %p.6 = getelementptr i8, ptr %p.5, i64 1
+  %p.7 = getelementptr i8, ptr %p.6, i64 1
+  %p.8.alias = getelementptr i8, ptr %p.7, i64 1
+; CHECK-NOT: store i32 42, ptr %p.8.alias.i, align 4, !noalias ![[ALIAS0:[0-9]+]]
+  store i32 42, ptr %p.8.alias
+  ret i32 %v
+}
Index: llvm/lib/Transforms/Utils/InlineFunction.cpp
===================================================================
--- llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -1068,15 +1068,41 @@
       SmallPtrSet<const Value *, 4> ObjSet;
       SmallVector<Metadata *, 4> Scopes, NoAliases;
 
+      bool ObjNotIdentified = false;
       SmallSetVector<const Argument *, 4> NAPtrArgs;
       for (const Value *V : PtrArgs) {
         SmallVector<const Value *, 4> Objects;
         getUnderlyingObjects(V, Objects, /* LI = */ nullptr);
 
+        // It is not guaranteed that getUnderlyingObjects produce identifiable
+        // object. In this case, try a second walk starting from previous
+        // result. If the end result is different, it is possible that first
+        // walk exited early due to MaxLookup limit.
+        if (!all_of(Objects, isIdentifiedObject)) {
+          SmallVector<const Value *, 4> MoreObjects;
+          DenseMap<const Value *, bool> Objs;
+          for (const Value *V : Objects)
+            getUnderlyingObjects(V, MoreObjects, /* LI = */ nullptr);
+
+          for (const Value *V : Objects)
+            Objs[V] = true;
+
+          for (const Value *V : MoreObjects)
+            if (Objs.find(V) == Objs.end()) {
+              ObjNotIdentified = true;
+              break;
+            }
+        }
+
         for (const Value *O : Objects)
           ObjSet.insert(O);
       }
 
+      // Be conservative since getUnderlyingObjects stopped the walk in the
+      // middle.
+      if (ObjNotIdentified)
+        continue;
+
       // Figure out if we're derived from anything that is not a noalias
       // argument.
       bool CanDeriveViaCapture = false, UsesAliasingPtr = false;


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