This is a recommit of the patch without changes. The reason for
the revert has been addressed in D117679.
-----
The user scanning loop above looks through pointer casts, so we
also need to strip pointer casts in the capture check. Previously
the source was incorrectly considered not captured if a bitcast
was passed to the call.
This is a recommit of the patch without changes. The reason for
the revert has been addressed in D117679.
-----
Call slot optimization is currently supposed to be prevented if
the call can capture the source pointer. Due to an implementation
bug, this check currently doesn't trigger if a bitcast of the source
pointer is passed instead. I'm somewhat afraid of the fallout of
fixing this bug (due to heavy reliance on call slot optimization
in rust), so I'd like to strengthen the capture reasoning a bit first.
In particular, I believe that the capture is fine as long as a)
the call itself cannot depend on the pointer identity, because
neither dest has been captured before/at nor src before the
call and b) there is no potential use of the captured pointer
before the lifetime of the source alloca ends, either due to
lifetime.end or a return from a function. At that point the
potentially captured pointer becomes dangling.
Differential Revision: https://reviews.llvm.org/D115615
This casued a miscompile due to call slot optimization replacing a call
argument without considering the call's !noalias metadata, see discussion on
the code review.
> Call slot optimization is currently supposed to be prevented if
> the call can capture the source pointer. Due to an implementation
> bug, this check currently doesn't trigger if a bitcast of the source
> pointer is passed instead. I'm somewhat afraid of the fallout of
> fixing this bug (due to heavy reliance on call slot optimization
> in rust), so I'd like to strengthen the capture reasoning a bit first.
>
> In particular, I believe that the capture is fine as long as a)
> the call itself cannot depend on the pointer identity, because
> neither dest has been captured before/at nor src before the
> call and b) there is no potential use of the captured pointer
> before the lifetime of the source alloca ends, either due to
> lifetime.end or a return from a function. At that point the
> potentially captured pointer becomes dangling.
>
> Differential Revision: https://reviews.llvm.org/D115615
Also reverting the dependent commit:
> [MemCpyOpt] Look through pointer casts when checking capture
>
> The user scanning loop above looks through pointer casts, so we
> also need to strip pointer casts in the capture check. Previously
> the source was incorrectly considered not captured if a bitcast
> was passed to the call.
This reverts commit 487a34ed9d7d24a7b1fb388c8856c784a459b22b
and 00e6869463ae6023d0d48f30de8511d6d748b14f.
The user scanning loop above looks through pointer casts, so we
also need to strip pointer casts in the capture check. Previously
the source was incorrectly considered not captured if a bitcast
was passed to the call.
Call slot optimization is currently supposed to be prevented if
the call can capture the source pointer. Due to an implementation
bug, this check currently doesn't trigger if a bitcast of the source
pointer is passed instead. I'm somewhat afraid of the fallout of
fixing this bug (due to heavy reliance on call slot optimization
in rust), so I'd like to strengthen the capture reasoning a bit first.
In particular, I believe that the capture is fine as long as a)
the call itself cannot depend on the pointer identity, because
neither dest has been captured before/at nor src before the
call and b) there is no potential use of the captured pointer
before the lifetime of the source alloca ends, either due to
lifetime.end or a return from a function. At that point the
potentially captured pointer becomes dangling.
Differential Revision: https://reviews.llvm.org/D115615
The MemorySSA-based implementation has been enabled for a few months
(since D94376). This patch drops the old MDA-based implementation
entirely.
I've kept this to only the basic cleanup of dropping various
conditions -- the code could be further cleaned up now that there
is only one implementation.
Differential Revision: https://reviews.llvm.org/D102113
This adds an -enable-memcpyopt-memoryssa option that currently does
nothing apart from requiring MSSA as a dependency. The tests are
split to run both with the option disabled and enabled. I went with
this rather than the separate directory DSE uses, as I found it
convenient to have a direct side-by-side comparison of differences.
Differential Revision: https://reviews.llvm.org/D89206
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
Note, this was reviewed (and more details are in) http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20151109/312083.html
These intrinsics currently have an explicit alignment argument which is
required to be a constant integer. It represents the alignment of the
source and dest, and so must be the minimum of those.
This change allows source and dest to each have their own alignments
by using the alignment attribute on their arguments. The alignment
argument itself is removed.
There are a few places in the code for which the code needs to be
checked by an expert as to whether using only src/dest alignment is
safe. For those places, they currently take the minimum of src/dest
alignments which matches the current behaviour.
For example, code which used to read:
call void @llvm.memcpy.p0i8.p0i8.i32(i8* %dest, i8* %src, i32 500, i32 8, i1 false)
will now read:
call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 8 %dest, i8* align 8 %src, i32 500, i1 false)
For out of tree owners, I was able to strip alignment from calls using sed by replacing:
(call.*llvm\.memset.*)i32\ [0-9]*\,\ i1 false\)
with:
$1i1 false)
and similarly for memmove and memcpy.
I then added back in alignment to test cases which needed it.
A similar commit will be made to clang which actually has many differences in alignment as now
IRBuilder can generate different source/dest alignments on calls.
In IRBuilder itself, a new argument was added. Instead of calling:
CreateMemCpy(Dst, Src, getInt64(Size), DstAlign, /* isVolatile */ false)
you now call
CreateMemCpy(Dst, Src, getInt64(Size), DstAlign, SrcAlign, /* isVolatile */ false)
There is a temporary class (IntegerAlignment) which takes the source alignment and rejects
implicit conversion from bool. This is to prevent isVolatile here from passing its default
parameter to the source alignment.
Note, changes in future can now be made to codegen. I didn't change anything here, but this
change should enable better memcpy code sequences.
Reviewed by Hal Finkel.
llvm-svn: 253511
