[flang-commits] [flang] [flang] Don't pass a hidden length for BIND(C) character dummy arguments (PR #224582)

[Tom Eccles via flang-commits]

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@@ -1274,6 +1274,15 @@ class Fortran::lower::CallInterfaceImpl {
             fir::CharacterType::getSingleton(&mlirContext, dynamicType.kind());
         addFirOperand(charTy, nextPassedArgPosition(), Property::Value, attrs);
         addPassedArg(PassEntityBy::Value, entity, characteristics);
+      } else if (isBindC && dynamicType.knownLength().value_or(0) == 1) {
+        // Pass as fir.ref: a BIND(C) procedure uses the C calling convention,
+        // which has no hidden length argument. Semantics requires a BIND(C)
+        // character dummy to have a length of 1, so the length is already
+        // known to both sides and carries no information.
+        mlir::Type refTy = fir::ReferenceType::get(type);
+        addFirOperand(refTy, nextPassedArgPosition(), Property::BaseAddress,
+                      attrs);
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tblah wrote:

I am not sure that the string is guaranteed to be null terminated as the C programme would expect. I think it needs a copy with the extra NULL character.

https://github.com/llvm/llvm-project/pull/224582