[llvm] [Inliner] Propagate callee argument memory access attributes before inlining (PR #89024)

[Nikita Popov via llvm-commits]

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@@ -1344,6 +1344,71 @@ static bool MayContainThrowingOrExitingCallAfterCB(CallBase *Begin,
       ++BeginIt, End->getIterator(), InlinerAttributeWindow + 1);
 }
 
+// Add attributes from CB params and Fn attributes that can always be propagated
+// to the corresponding argument / inner callbases.
+static void AddParamAndFnBasicAttributes(const CallBase &CB,
+                                         ValueToValueMapTy &VMap) {
+  auto *CalledFunction = CB.getCalledFunction();
+  auto &Context = CalledFunction->getContext();
+
+  // Collect valid attributes for all params.
+  SmallVector<AttrBuilder> ValidParamAttrs;
+  bool HasAttrToPropagate = false;
+
+  for (unsigned I = 0, E = CB.arg_size(); I < E; ++I) {
+    ValidParamAttrs.emplace_back(AttrBuilder{CB.getContext()});
+    // Access attributes can be propagated to any param with the same underlying
+    // object as the argument.
+    if (CB.paramHasAttr(I, Attribute::ReadNone))
+      ValidParamAttrs.back().addAttribute(Attribute::ReadNone);
+    if (CB.paramHasAttr(I, Attribute::ReadOnly))
+      ValidParamAttrs.back().addAttribute(Attribute::ReadOnly);
+    if (CB.paramHasAttr(I, Attribute::WriteOnly))
+      ValidParamAttrs.back().addAttribute(Attribute::WriteOnly);
+    HasAttrToPropagate |= ValidParamAttrs.back().hasAttributes();
+  }
+
+  // Won't be able to propagate anything.
+  if (!HasAttrToPropagate)
+    return;
+
+  for (BasicBlock &BB : *CalledFunction) {
+    for (Instruction &Ins : BB) {
+      if (const auto *InnerCB = dyn_cast<CallBase>(&Ins)) {
+        if (auto *NewInnerCB =
+                dyn_cast_or_null<CallBase>(VMap.lookup(InnerCB))) {
+          AttributeList AL = NewInnerCB->getAttributes();
+          for (unsigned I = 0, E = InnerCB->arg_size(); I < E; ++I) {
+            // Check if the underlying value for the parameter is an argument.
+            const Value *UnderlyingV =
+                getUnderlyingObject(InnerCB->getArgOperand(I));
+            if (const Argument *Arg = dyn_cast<Argument>(UnderlyingV)) {
+              unsigned ArgNo = Arg->getArgNo();
+              // If so, propagate its access attributes.
+              AL = AL.addParamAttributes(Context, I, ValidParamAttrs[ArgNo]);
+              // We can have conflicting attributes from the inner callsite and
+              // to-be-inlined callsite. In that case, choose the most
+              // restrictive.
+
+              // readonly + writeonly means we can never deref so make readnone.
+              if (AL.hasParamAttr(I, Attribute::ReadOnly) &&
+                  AL.hasParamAttr(I, Attribute::WriteOnly))
+                AL = AL.addParamAttribute(Context, I, Attribute::ReadNone);
+
+              // If have readnone, need to clear readonly/writeonly
+              if (AL.hasParamAttr(I, Attribute::ReadNone)) {
+                AL = AL.removeParamAttribute(Context, I, Attribute::ReadOnly);
+                AL = AL.removeParamAttribute(Context, I, Attribute::WriteOnly);
+              }
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nikic wrote:

You could also have a conflict with writable.

https://github.com/llvm/llvm-project/pull/89024