workaround for nativeclient issue 3798, wrong alignment on copy of a byval struct argument

1 files changed, 10 insertions, 0 deletions

diff --git a/lib/Transforms/NaCl/ExpandByVal.cpp b/lib/Transforms/NaCl/ExpandByVal.cpp
index 0220cafb88..07fdf89570 100644
--- a/lib/Transforms/NaCl/ExpandByVal.cpp
+++ b/lib/Transforms/NaCl/ExpandByVal.cpp
@@ -139,6 +139,16 @@ static bool ExpandCall(DataLayout *DL, InstType *Call) {
       // the alignment attribute specifies "the alignment of the stack
       // slot to form and the known alignment of the pointer specified
       // to the call site".
+
+      // XXX EMSCRIPTEN: we also need to take into account the "intrinsic"
+      //                 alignment of the structure being copied. The
+      //                 arg align may be "0" but the struct could only be
+      //                 2-byte aligned for example. This seems to contradict
+      //                 the quote above, so this might be a bug elsewhere
+      //                 in LLVM. FIXME
+      //                 https://code.google.com/p/nativeclient/issues/detail?id=3798
+      Alignment = AllocAlignment;
+
       Instruction *MemCpy = Builder.CreateMemCpy(CopyBuf, ArgPtr, ArgSize,
                                                  Alignment);
       MemCpy->setDebugLoc(Call->getDebugLoc());