[flang-commits] [flang] [mlir] [mlir][func] Refactor FuncToLLVM discardable attributes algorithm (PR #188232)

[Mehdi Amini via flang-commits]

================
@@ -59,19 +61,82 @@ static bool shouldUseBarePtrCallConv(Operation *op,
          typeConverter->getOptions().useBarePtrCallConv;
 }
 
+static bool isDiscardableAttr(StringRef name) {
+  return name == linkageAttrName || name == varargsAttrName ||
+         name == LLVM::LLVMDialect::getReadnoneAttrName();
+}
+
 /// Only retain those attributes that are not constructed by
 /// `LLVMFuncOp::build`.
 static void filterFuncAttributes(FunctionOpInterface func,
                                  SmallVectorImpl<NamedAttribute> &result) {
   for (const NamedAttribute &attr : func->getDiscardableAttrs()) {
-    if (attr.getName() == linkageAttrName ||
-        attr.getName() == varargsAttrName ||
-        attr.getName() == LLVM::LLVMDialect::getReadnoneAttrName())
+    if (isDiscardableAttr(attr.getName().strref()))
       continue;
     result.push_back(attr);
   }
 }
 
+/// Add custom lowered funcOp to llvm.func attributes here.
+struct LoweredFuncAttrs {
+  LLVM::LLVMFuncOp::Properties properties;
+  NamedAttrList discardableAttrs;
+};
+
+/// Lower discardable function attributes on `func.func` to attributes expected
+/// by `llvm.func`.static FailureOr<LoweredFuncAttrs>
+static FailureOr<LoweredFuncAttrs>
+lowerFuncAttributes(FunctionOpInterface func) {
+  MLIRContext *ctx = func->getContext();
+  LoweredFuncAttrs lowered;
+
+  llvm::SmallDenseSet<StringRef> odsAttrNames(
+      LLVM::LLVMFuncOp::getAttributeNames().begin(),
+      LLVM::LLVMFuncOp::getAttributeNames().end());
+
+  NamedAttrList inherentAttrs;
+
+  for (const NamedAttribute &attr : func->getDiscardableAttrs()) {
+    StringRef attrName = attr.getName().strref();
+
+    if (odsAttrNames.contains(attrName)) {
+      LDBG() << "LLVM specific attributes: " << attrName
+             << "should use llvm.* prefix, discarding it";
+      continue;
+    }
+
+    StringRef inherent = attrName;
+    if (inherent.consume_front("llvm.") && odsAttrNames.contains(inherent)) {
+      inherentAttrs.set(inherent, attr.getValue()); // collect inherent attrs
+    } else {
+      lowered.discardableAttrs.push_back(attr);
+    }
----------------
joker-eph wrote:

```suggestion
    if (inherent.consume_front("llvm.") && odsAttrNames.contains(inherent))
      inherentAttrs.set(inherent, attr.getValue()); // collect inherent attrs
    else
      lowered.discardableAttrs.push_back(attr);
```

Nit: no trivial braces

https://github.com/llvm/llvm-project/pull/188232