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

[via cfe-commits]

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@@ -1381,21 +1405,58 @@ 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)
-          continue;
+        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, only remove from the
+          // existing AL if the region of the existing param is smaller than
+          // what we can propagate. AttributeList's merge API honours the
+          // already existing attribute value so we choose the "better"
+          // attribute by removing if the existing one is worse.
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goldsteinn wrote:

https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/Utils/InlineFunction.cpp#L1500

Is a bit confusing...

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