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When passing a parameter using the 'byval' mechanism, inline code needs to be used

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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
This commit is contained in:
Duncan Sands 2010-11-05 15:20:29 +00:00
parent f8254d6473
commit 69300a2f47
1 changed files with 2 additions and 0 deletions
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lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -3283,6 +3283,8 @@ static SDValue getMemcpyLoadsAndStores(SelectionDAG &DAG, DebugLoc dl,
// 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;