this was a tree of hashtables, and a query recursed into the table for the immediate dominator ad infinitum
if the initial lookup failed. This led to really bad performance on tall, narrow CFGs.
We can instead replace it with what is conceptually a multimap of value numbers to leaders (actually
represented by a hashtable with a list of Value*'s as the value type), and then
determine which leader from that set to use very cheaply thanks to the DFS numberings maintained by
DominatorTree. Because there are typically few duplicates of a given value, this scan tends to be
quite fast. Additionally, we use a custom linked list and BumpPtr allocation to avoid any unnecessary
allocation in representing the value-side of the multimap.
This change brings with it a 15% (!) improvement in the total running time of GVN on 403.gcc, which I
think is pretty good considering that includes all the "real work" being done by MemDep as well.
The one downside to this approach is that we can no longer use GVN to perform simple conditional progation,
but that seems like an acceptable loss since we now have LVI and CorrelatedValuePropagation to pick up
the slack. If you see conditional propagation that's not happening, please file bugs against LVI or CVP.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119714 91177308-0d34-0410-b5e6-96231b3b80d8
instruction. Any that may be expanded otherwise by MC lowering should
override this value. rdar://8683274
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refusing to optimize two memcpy's like this:
copy A <- B
copy C <- A
if it couldn't prove that noalias(B,C). We can eliminate
the copy by producing a memmove instead of memcpy.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119694 91177308-0d34-0410-b5e6-96231b3b80d8
there is no need to check to see if the source and dest of a memcpy are noalias,
behavior is undefined if not.
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if it is passed as a byval argument. The byval argument will just be a
read, so it is safe to read from the original global instead. This allows
us to promote away the %agg.tmp alloca in PR8582
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sahf movl 344(%rdi),%r14d
we used to produce:
t.s:2:1: error: unexpected token in argument list
^
we now produce:
t.s:1:11: error: unexpected token in argument list
sahf movl 344(%rdi),%r14d
^
rdar://8581401
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The attached patch fixes IRBuilder and the NoFolder class so that when
NoFolder is used the instructions it generates are treated just like
the ones IRBuilder creates directly (insert into block, assign them a
name and debug info, as applicable).
It does this by
1) having NoFolder return Instruction*s instead of Value*s,
2) having IRBuilder call Insert(Value, Name) on values obtained from
the folder like it does on instructions it creates directly, and
3) adding an Insert(Constant*, const Twine& = "") overload which just
returns the constant so that the other folders shouldn't have any
extra overhead as long as inlining is enabled.
While I was there, I also added some missing (CreateFNeg and various
Create*Cast) methods to NoFolder.
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and testing is easier. A good example is the unknown-location.ll test that
now can just look for ".loc 1 0 0". We also don't use a DW_LNE_set_address for
every address change anymore.
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memset; we may need it to decide between MOVAPS and MOVUPS
later. Adjust a test that was looking for wrong code.
PR 3866 / 8675131.
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Some of these maps may merge in the future, but for now it's convenient to have
a utility function for them.
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memoize the results. This improves compile time in code which highly complex
expressions which get queried many times.
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