[LLVMdev] Aliasing caused by MemCpyOptimizer (PR18304)

[Maciej Piechotka]

On Sun, 2014-06-15 at 13:57 +0200, David Wiberg wrote:
> Hello all,
> 
> PR18304 show an example where MemCpyOptimizer can cause pointers to
> alias. Adding a requirement that the called function does not capture
> the source pointer fixes the issue but it will also decrease the
> number of opportunities for the transform.
> 
> Does this seem like the correct direction for a fix?
> Will it be too restrictive?
> 
> Among the regression tests the proposed change causes failures in the
> following files:
> LLVM :: Transforms/MemCpyOpt/2008-02-24-MultipleUseofSRet.ll
> LLVM :: Transforms/MemCpyOpt/2008-03-13-ReturnSlotBitcast.ll
> LLVM :: Transforms/MemCpyOpt/loadstore-sret.ll
> LLVM :: Transforms/MemCpyOpt/memcpy.ll
> LLVM :: Transforms/MemCpyOpt/sret.ll
> 
> If the solution seems correct my idea is to add the "nocapture"
> attribute to the functions called in the test files (assuming they
> don't capture the source pointer) to get the same test behavior as
> before.
> 
> Best regards
> David

I'm not sure about LLVM coding/patch standards but I imagine that adding
a regression test in the patch might be nice.

Best regards
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