[llvm-commits] [llvm] r118275 - /llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

[Duncan Sands]

Author: baldrick
Date: Fri Nov  5 10:20:29 2010
New Revision: 118275

URL: http://llvm.org/viewvc/llvm-project?rev=118275&view=rev
Log:
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...

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=118275&r1=118274&r2=118275&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Fri Nov  5 10:20:29 2010
@@ -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;