Summary:
Extract FindAvailablePtrLoadStore out of FindAvailableLoadedValue.
Prepare for upcoming change which will do phi-translation for load on
phi pointer in jump threading SimplifyPartiallyRedundantLoad.
This is in preparation for https://reviews.llvm.org/D30543
Reviewers: efriedma, sanjoy, davide, dberlin
Reviewed By: davide
Subscribers: junbuml, davide, llvm-commits
Differential Revision: https://reviews.llvm.org/D30524
llvm-svn: 298216
Summary: While scanning predecessors to find an available loaded value, if the predecessor has a single predecessor, we can continue scanning through the single predecessor.
Reviewers: mcrosier, rengolin, reames, davidxl, haicheng
Reviewed By: rengolin
Subscribers: zzheng, llvm-commits
Differential Revision: https://reviews.llvm.org/D29200
llvm-svn: 293896
Summary:
We were trying to add APInt values with different bit sizes after
visiting an addrspacecast instruction which changed the bit width
of the pointer.
Reviewers: majnemer, hfinkel
Subscribers: hfinkel, wdng, llvm-commits
Differential Revision: https://reviews.llvm.org/D24774
llvm-svn: 285407
There were paths where we wouldn't populate the visited set, causing us
to recurse forever if an SSA variable was defined in terms of itself.
This fixes PR30210.
llvm-svn: 280191
Summary:
The correctness fix here is that when we CSE a load with another load,
we need to combine the metadata on the two loads. This matches the
behavior of other passes, like instcombine and GVN.
There's also a minor optimization improvement here: for load PRE, the
aliasing metadata on the inserted load should be the same as the
metadata on the original load. Not sure why the old code was throwing
it away.
Issue found by inspection.
Differential Revision: http://reviews.llvm.org/D21460
llvm-svn: 277977
For functions which are known to return their argument,
isDereferenceableAndAlignedPointer can examine the argument value.
Differential Revision: http://reviews.llvm.org/D9384
llvm-svn: 275038
We can fold truncs whose operand feeds from a load, if the trunc value
is available through a prior load/store.
This change is from: http://reviews.llvm.org/D21246, which folded the
trunc but missed the bitcast or ptrtoint/inttoptr required in the RAUW
call, when the load type didnt match the prior load/store type.
Differential Revision: http://reviews.llvm.org/D21791
llvm-svn: 274853
This actually uncovered a surprisingly large chain of ultimately unused
TLI args.
From what I can gather, this argument is a remnant of when
isKnownNonNull would look at the TLI directly.
The current approach seems to be that InferFunctionAttrs runs early in
the pipeline and uses TLI to annotate the TLI-dependent non-null
information as return attributes.
This also removes the dependence of functionattrs on TLI altogether.
llvm-svn: 274455
Summary:
This instcombine rule folds away trunc operations that have value available from a prior load or store.
This kind of code can be generated as a result of GVN widening the load or from source code as well.
Reviewers: reames, majnemer, sanjoy
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D21246
llvm-svn: 273608
Now that `Value::getPointerDereferenceableBytes` looks beyond just
attributes, the name `isDereferenceableFromAttribute` is misleading.
Just inline the function, since it is small and only used once.
llvm-svn: 271456
... and merge into `Value::getPointerDereferenceableBytes`. This was
suggested by Artur Pilipenko in D20764 -- since we no longer allow loads
of unsized types, there is no need anymore to have this special logic.
llvm-svn: 271455
Summary:
Change some of the internal interfaces in Loads.cpp to keep track of the
number of bytes we're trying to prove dereferenceable using an explicit
`Size` parameter.
Before this, the `Size` parameter was implicitly inferred from the
pointee type of the pointer whose dereferenceability we were trying to
prove, causing us to be conservative around bitcasts. This was
unfortunate since bitcast instructions are no-ops and should never
break optimizations. With an explicit `Size` parameter, we're more
precise (as shown in the test cases), and the code is simpler.
We should eventually move towards a `DerefQuery` struct that groups
together a base pointer, an offset, a size and an alignment; but this
patch is a first step.
Reviewers: apilipenko, dblaikie, hfinkel, reames
Subscribers: mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D20764
llvm-svn: 271406
Extract a part of isDereferenceableAndAlignedPointer functionality to Value:
Reviewed By: hfinkel, sanjoy
Differential Revision: http://reviews.llvm.org/D17611
llvm-svn: 269190
Extract a part of isDereferenceableAndAlignedPointer functionality to Value::getPointerDerferecnceableBytes. Currently it's a NFC, but in future I'm going to accumulate all the logic about value dereferenceability in this function similarly to Value::getPointerAlignment function (D16144).
Reviewed By: reames
Differential Revision: http://reviews.llvm.org/D17572
llvm-svn: 267708
This is required to use this function from isSafeToSpeculativelyExecute
Reviewed By: hfinkel
Differential Revision: http://reviews.llvm.org/D16231
llvm-svn: 267692
This change adds a couple of test cases to make sure FindAvailableLoadedValue does the right thing. At the moment, the code added is dead, but separating it makes follow on changes far more obvious.
llvm-svn: 266999
Summary:
Fixes PR26774.
If you're aware of the issue, feel free to skip the "Motivation"
section and jump directly to "This patch".
Motivation:
I define "refinement" as discarding behaviors from a program that the
optimizer has license to discard. So transforming:
```
void f(unsigned x) {
unsigned t = 5 / x;
(void)t;
}
```
to
```
void f(unsigned x) { }
```
is refinement, since the behavior went from "if x == 0 then undefined
else nothing" to "nothing" (the optimizer has license to discard
undefined behavior).
Refinement is a fundamental aspect of many mid-level optimizations done
by LLVM. For instance, transforming `x == (x + 1)` to `false` also
involves refinement since the expression's value went from "if x is
`undef` then { `true` or `false` } else { `false` }" to "`false`" (by
definition, the optimizer has license to fold `undef` to any non-`undef`
value).
Unfortunately, refinement implies that the optimizer cannot assume
that the implementation of a function it can see has all of the
behavior an unoptimized or a differently optimized version of the same
function can have. This is a problem for functions with comdat
linkage, where a function can be replaced by an unoptimized or a
differently optimized version of the same source level function.
For instance, FunctionAttrs cannot assume a comdat function is
actually `readnone` even if it does not have any loads or stores in
it; since there may have been loads and stores in the "original
function" that were refined out in the currently visible variant, and
at the link step the linker may in fact choose an implementation with
a load or a store. As an example, consider a function that does two
atomic loads from the same memory location, and writes to memory only
if the two values are not equal. The optimizer is allowed to refine
this function by first CSE'ing the two loads, and the folding the
comparision to always report that the two values are equal. Such a
refined variant will look like it is `readonly`. However, the
unoptimized version of the function can still write to memory (since
the two loads //can// result in different values), and selecting the
unoptimized version at link time will retroactively invalidate
transforms we may have done under the assumption that the function
does not write to memory.
Note: this is not just a problem with atomics or with linking
differently optimized object files. See PR26774 for more realistic
examples that involved neither.
This patch:
This change introduces a new set of linkage types, predicated as
`GlobalValue::mayBeDerefined` that returns true if the linkage type
allows a function to be replaced by a differently optimized variant at
link time. It then changes a set of IPO passes to bail out if they see
such a function.
Reviewers: chandlerc, hfinkel, dexonsmith, joker.eph, rnk
Subscribers: mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D18634
llvm-svn: 265762
This is a part of the refactoring to unify isSafeToLoadUnconditionally and isDereferenceablePointer functions. In subsequent change I'm going to eliminate isDerferenceableAndAlignedPointer from Loads API, leaving isSafeToLoadSpecualtively the only function to check is load instruction can be speculated.
Reviewed By: hfinkel
Differential Revision: http://reviews.llvm.org/D16180
llvm-svn: 261736
This is a part of the refactoring to unify isSafeToLoadUnconditionally and isDereferenceablePointer functions. In the subsequent change isSafeToSpeculativelyExecute will be modified to use isSafeToLoadUnconditionally instead of isDereferenceableAndAlignedPointer.
Reviewed By: reames
Differential Revision: http://reviews.llvm.org/D16227
llvm-svn: 260520
Xin Tong
Jun Bum Lim
Tom Stellard
David Majnemer
Eli Friedman
Hal Finkel
Anna Thomas
Sean Silva
Reid Kleckner
Benjamin Kramer
Sanjoy Das
Artur Pilipenko
Philip Reames
Eduard Burtescu