[llvm] Attributor: Do not assume function context in AANoCapture (PR #91462)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

If the calling function has the null_pointer_is_valid attribute, somehow a null constant reaches here. I'm not sure why exactly, it doesn't happen for other types of constants.

Fixes #<!-- -->87856

---
Full diff: https://github.com/llvm/llvm-project/pull/91462.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/IPO/AttributorAttributes.cpp (+8-2) 
- (added) llvm/test/Transforms/Attributor/issue87856.ll (+61) 


``````````diff
diff --git a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
index 41b66aafe7d34..1b3bf3c732ed0 100644
--- a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -5690,6 +5690,9 @@ bool AANoCapture::isImpliedByIR(Attributor &A, const IRPosition &IRP,
     return V.use_empty();
 
   // You cannot "capture" null in the default address space.
+  //
+  // FIXME: This should use NullPointerIsDefined to account for the function
+  // attribute.
   if (isa<UndefValue>(V) || (isa<ConstantPointerNull>(V) &&
                              V.getType()->getPointerAddressSpace() == 0)) {
     return true;
@@ -5899,10 +5902,13 @@ ChangeStatus AANoCaptureImpl::updateImpl(Attributor &A) {
 
   const Function *F =
       isArgumentPosition() ? IRP.getAssociatedFunction() : IRP.getAnchorScope();
-  assert(F && "Expected a function!");
-  const IRPosition &FnPos = IRPosition::function(*F);
+
+  // TODO: Is the checkForAllUses below useful for constants?
+  if (!F)
+    return indicatePessimisticFixpoint();
 
   AANoCapture::StateType T;
+  const IRPosition &FnPos = IRPosition::function(*F);
 
   // Readonly means we cannot capture through memory.
   bool IsKnown;
diff --git a/llvm/test/Transforms/Attributor/issue87856.ll b/llvm/test/Transforms/Attributor/issue87856.ll
new file mode 100644
index 0000000000000..4da29cc4448d4
--- /dev/null
+++ b/llvm/test/Transforms/Attributor/issue87856.ll
@@ -0,0 +1,61 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --version 4
+; RUN: opt -S -passes=attributor < %s | FileCheck %s
+
+define void @null_ptr_is_valid_call_with_null() #0 {
+; CHECK-LABEL: define void @null_ptr_is_valid_call_with_null(
+; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    call void @store_as0(ptr nofree noundef writeonly align 4294967296 null) #[[ATTR4:[0-9]+]]
+; CHECK-NEXT:    ret void
+;
+  call void @store_as0(ptr null)
+  ret void
+}
+
+define void @null_ptr_is_valid_call_with_undef() #0 {
+; CHECK-LABEL: define void @null_ptr_is_valid_call_with_undef(
+; CHECK-SAME: ) #[[ATTR1:[0-9]+]] {
+; CHECK-NEXT:    call void @store_as0(ptr undef) #[[ATTR4]]
+; CHECK-NEXT:    ret void
+;
+  call void @store_as0(ptr undef)
+  ret void
+}
+
+define void @store_as0(ptr %0) {
+; CHECK-LABEL: define void @store_as0(
+; CHECK-SAME: ptr nocapture nofree noundef nonnull writeonly align 2 dereferenceable(2) [[TMP0:%.*]]) #[[ATTR2:[0-9]+]] {
+; CHECK-NEXT:    store i16 0, ptr [[TMP0]], align 2
+; CHECK-NEXT:    ret void
+;
+  store i16 0, ptr %0, align 2
+  ret void
+}
+
+define void @call_store_as1() {
+; CHECK-LABEL: define void @call_store_as1(
+; CHECK-SAME: ) #[[ATTR3:[0-9]+]] {
+; CHECK-NEXT:    call void @store_as1(ptr addrspace(1) nocapture nofree noundef writeonly align 4294967296 null) #[[ATTR4]]
+; CHECK-NEXT:    ret void
+;
+  call void @store_as1(ptr addrspace(1) null)
+  ret void
+}
+
+define void @store_as1(ptr addrspace(1) %arg) {
+; CHECK-LABEL: define void @store_as1(
+; CHECK-SAME: ptr addrspace(1) nocapture nofree noundef writeonly align 2 dereferenceable_or_null(2) [[ARG:%.*]]) #[[ATTR2]] {
+; CHECK-NEXT:    store i16 0, ptr addrspace(1) [[ARG]], align 2
+; CHECK-NEXT:    ret void
+;
+  store i16 0, ptr addrspace(1) %arg, align 2
+  ret void
+}
+
+attributes #0 = { null_pointer_is_valid }
+;.
+; CHECK: attributes #[[ATTR0]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(write) }
+; CHECK: attributes #[[ATTR1]] = { mustprogress nofree norecurse nosync nounwind null_pointer_is_valid willreturn memory(none) }
+; CHECK: attributes #[[ATTR2]] = { mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: write) }
+; CHECK: attributes #[[ATTR3]] = { mustprogress nofree norecurse nosync nounwind willreturn memory(none) }
+; CHECK: attributes #[[ATTR4]] = { nofree nosync nounwind willreturn memory(write) }
+;.

``````````

</details>


https://github.com/llvm/llvm-project/pull/91462