When passing a parameter using the 'byval' mechanism, inline code needs to be used
to perform the copy, which may be of lots of memory [*]. It would be good if the
fall-back code generated something reasonable, i.e. did the copy in a loop, rather
than vast numbers of loads and stores. Add a note about this. Currently target
specific code seems to always kick in so this is more of a theoretical issue rather
than a practical one now that X86 has been fixed.
[*] It's amazing how often people pass mega-byte long arrays by copy...
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118275 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 0840bd7..5477e7b 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3283,6 +3283,8 @@
// Expand memcpy to a series of load and store ops if the size operand falls
// below a certain threshold.
+ // TODO: In the AlwaysInline case, if the size is big then generate a loop
+ // rather than maybe a humongous number of loads and stores.
const TargetLowering &TLI = DAG.getTargetLoweringInfo();
std::vector<EVT> MemOps;
bool DstAlignCanChange = false;