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Summary:
It seems that negative offset was accidentally allowed in D17967.
AFAICT small negative offset should be valid (always raise segfault) on all archs that I'm aware of (especially x86, which is the only one with this optimization enabled) and such case can be useful when loading hiden metadata from an object.
However, like the positive side, it should only be done within a certain limit.
For now, use the same limit on the positive side for the negative side.
A separate option can be added if needs appear.
Reviewers: mcrosier, skatkov
Reviewed By: skatkov
Subscribers: sanjoy, llvm-commits
Differential Revision: https://reviews.llvm.org/D38925
llvm-svn: 315991
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Summary:
This change allows usage of store instruction for implicit null check.
Memory Aliasing Analisys is not used and change conservatively supposes
that any store and load may access the same memory. As a result
re-ordering of store-store, store-load and load-store is prohibited.
Patch by Serguei Katkov!
Reviewers: reames, sanjoy
Reviewed By: sanjoy
Subscribers: atrick, llvm-commits
Differential Revision: https://reviews.llvm.org/D29400
llvm-svn: 294338
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Summary:
This change allows a re-order of two intructions if their uses
are overlapped.
Patch by Serguei Katkov!
Reviewers: reames, sanjoy
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D29120
llvm-svn: 293775
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liveness.
The replaced load may have implicit-defs and those defs may be used
in the block of the original load. Make sure to update the liveness
accordingly.
This is a generalization of r267817.
llvm-svn: 268412
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After the layout of the basic blocks is set, the target may be able to get rid
of unconditional branches to fallthrough blocks that the generic code does not
catch. This happens any time TargetInstrInfo::AnalyzeBranch is not able to
analyze all the branches involved in the terminators sequence, while still
understanding a few of them.
In such situation, AnalyzeBranch can directly modify the branches if it has been
instructed to do so.
This patch takes advantage of that.
llvm-svn: 268328
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This operation may branch to the handler block and we do not want it
to happen anywhere within the basic block.
Moreover, by marking it "terminator and branch" the machine verifier
does not wrongly assume (because of AnalyzeBranch not knowing better)
the branch is analyzable. Indeed, the target was seeing only the
unconditional branch and not the faulting load op and thought it was
a simple unconditional block.
The machine verifier was complaining because of that and moreover,
other optimizations could have done wrong transformation!
In the process, simplify the representation of the handler block in
the faulting load op. Now, we directly reference the handler block
instead of using a label. This has the benefits of:
1. MC knows how to issue a label for a BB, so leave that to it.
2. Accessing the target BB from its label is painful, whereas it is
direct from a MBB operand.
Note: The 2 bytes offset in implicit-null-check.ll comes from the
fact the unconditional jumps are not removed anymore, as the whole
terminator sequence is not analyzable anymore.
Will fix it in a subsequence commit.
llvm-svn: 268327
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Summary:
This change generalizes the implicit null checks pass to work with
instructions that don't have any explicit register defs. This lets us
use X86's `cmp` against memory as faulting load instructions.
Reviewers: reames, JosephTremoulet
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D11286
llvm-svn: 242703
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Summary:
Before this change ImplicitNullChecks would only pick loads of the form:
```
test Reg, Reg
jz elsewhere
fallthrough:
movl 32(Reg), Reg2
```
but not (say)
```
test Reg, Reg
jz elsewhere
fallthrough:
inc Reg3
movl 32(Reg), Reg2
```
This change teaches ImplicitNullChecks to look through "unrelated"
instructions like `inc Reg3` when searching for a load instruction
to convert to a trapping load.
Reviewers: atrick, JosephTremoulet, reames
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D11044
llvm-svn: 241850
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Summary:
This change introduces a !make.implicit metadata that allows the
frontend to pre-select the set of explicit null checks that will be
considered for transformation into implicit null checks.
The reason for not using profiling data instead of !make.implicit is
explained in the change to `FaultMaps.rst`.
Reviewers: atrick, reames, pgavlin, JosephTremoulet
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D10824
llvm-svn: 241116
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Summary:
The parser is exercised by llvm-objdump using -print-fault-maps. As is
probably obvious, the code itself was "heavily inspired" by
http://reviews.llvm.org/D10434.
Reviewers: reames, atrick, JosephTremoulet
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D10491
llvm-svn: 240304
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Summary:
This change adds an "ImplicitNullChecks" target dependent pass. This
pass folds null checks into memory operation using the FAULTING_LOAD
pseudo-op introduced in previous patches.
Depends on D10197
Depends on D10199
Depends on D10200
Reviewers: reames, rnk, pgavlin, JosephTremoulet, atrick
Reviewed By: atrick
Subscribers: ab, JosephTremoulet, llvm-commits
Differential Revision: http://reviews.llvm.org/D10201
llvm-svn: 239743
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