[clang] [llvm] [Inliner] Propagate more attributes to params when inlining (PR #91101)

[Nikita Popov via llvm-commits]

================
@@ -1391,22 +1412,65 @@ static void AddParamAndFnBasicAttributes(const CallBase &CB,
 
       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));
-        const Argument *Arg = dyn_cast<Argument>(UnderlyingV);
-        if (!Arg)
+        // It's unsound or requires special handling to propagate attributes to
+        // byval arguments. For reach even if CalledFunction doesn't e.g. write
+        // to the argument (readonly), the call to NewInnerCB may write to its
+        // by-value copy.
+        if (AL.hasParamAttr(I, Attribute::ByVal))
           continue;
 
-        if (AL.hasParamAttr(I, Attribute::ByVal))
-          // It's unsound to propagate memory attributes to byval arguments.
-          // Even if CalledFunction doesn't e.g. write to the argument,
-          // the call to NewInnerCB may write to its by-value copy.
+        // Don't both propagating attrs to constants.
+        if (match(NewInnerCB->getArgOperand(I),
+                  llvm::PatternMatch::m_ImmConstant()))
           continue;
 
-        unsigned ArgNo = Arg->getArgNo();
+        // Check if the underlying value for the parameter is an argument.
+        const Argument *Arg = dyn_cast<Argument>(InnerCB->getArgOperand(I));
+        unsigned ArgNo;
+        if (Arg) {
+          ArgNo = Arg->getArgNo();
+          // For dereferenceable, dereferenceable_or_null, align, etc...
+          // we don't want to propagate if the existing param has the same
+          // attribute with "better" constraints. So  remove from the
+          // new AL if the region of the existing param is larger than
+          // what we can propagate.
+          AttrBuilder NewAL(Context);
+          for (auto Attr : ValidExactParamAttrs[ArgNo].attrs())
+            NewAL.addAttribute(Attr);
+          if (AL.getParamDereferenceableBytes(I) >
+              NewAL.getDereferenceableBytes())
+            NewAL.removeAttribute(Attribute::Dereferenceable);
+          if (AL.getParamDereferenceableOrNullBytes(I) >
+              NewAL.getDereferenceableOrNullBytes())
+            NewAL.removeAttribute(Attribute::Dereferenceable);
----------------
nikic wrote:

```suggestion
            NewAL.removeAttribute(Attribute::DereferenceableOrNull);
```

https://github.com/llvm/llvm-project/pull/91101