[flang-commits] [flang] [flang] Fix `getTypeSizeAndAlignment` for packed/tail-padded `RecordType` and `TRANSFER` gate (PR #220377)

[via flang-commits]

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@@ -1661,15 +1661,40 @@ fir::getTypeSizeAndAlignment(mlir::Location loc, mlir::Type ty,
   if (auto recTy = mlir::dyn_cast<fir::RecordType>(ty)) {
     std::uint64_t size = 0;
     unsigned short align = 1;
+    if (recTy.isPacked()) {
+      // LLVM packed structs (<{ ... }>) place fields back-to-back with no
+      // inter-field alignment padding and no tail padding.  Each component
+      // still occupies its allocation size (llvm::alignTo(storeSize, ABI
+      // alignment)), because LLVM's packed StructLayout advances by
+      // getTypeAllocSize, not getTypeStoreSize.  For example, x86 f80 has
+      // store size 10 bytes but ABI alignment 16 bytes, so its allocation
+      // size is 16 bytes; a packed {f80, i8} therefore occupies 17 bytes,
+      // not 11.  The packed struct's own ABI alignment is always 1.
+      for (auto component : recTy.getTypeList()) {
+        auto result =
+            getTypeSizeAndAlignment(loc, component.second, dl, kindMap);
+        if (!result)
+          return result;
+        auto [compSize, compAlign] = *result;
+        size += llvm::alignTo(compSize, compAlign); // allocation size per field
+      }
+      // Packed structs have no tail padding regardless of storeSizeOnly.
+      return std::pair{size, static_cast<unsigned short>(1)};
+    }
     for (auto component : recTy.getTypeList()) {
-      auto result = getTypeSizeAndAlignment(loc, component.second, dl, kindMap);
+      auto result = getTypeSizeAndAlignment(loc, component.second, dl, kindMap,
+                                            storeSizeOnly);
       if (!result)
         return result;
       auto [compSize, compAlign] = *result;
       size =
           llvm::alignTo(size, compAlign) + llvm::alignTo(compSize, compAlign);
       align = std::max(align, compAlign);
     }
+    // Include tail padding so the size matches the allocation size,
+    // unless the caller only wants the store size (no tail padding).
+    if (!storeSizeOnly)
+      size = llvm::alignTo(size, align);
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MattPD wrote:

This tail rounding changes how SystemZ passes arguments declared `BIND(C)` and `VALUE`. At `d6b2176126d7`, the lowering passes `{i32,i8}` and `{i16,i8}` records indirectly. At `eabf68933226`, the lowering passes them as `i64` and `i32`. Those argument types match SystemZ's GPR size cases.

Could the existing `struct-passing-systemz-reference.fir` test cover both record shapes and check their respective ABI classifications?


https://github.com/llvm/llvm-project/pull/220377