Summary:
In D62801, new function attribute `willreturn` was introduced. In short, a function with `willreturn` is guaranteed to come back to the call site(more precise definition is in LangRef).
In this patch, willreturn is annotated for LLVM intrinsics.
Reviewers: jdoerfert
Reviewed By: jdoerfert
Subscribers: jvesely, nhaehnle, sstefan1, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D64904
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@367184 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
The DeadStoreElimination pass now skips doing
PartialStoreMerging when stores overlap according to
OW_PartialEarlierWithFullLater and at least one of
the stores is having a store size that is different
from the size of the type being stored.
This solves problems seen in
https://bugs.llvm.org/show_bug.cgi?id=41949
for which we in the past could end up with
mis-compiles or assertions.
The content and location of the padding bits is not
formally described (or undefined) in the LangRef
at the moment. So the solution is chosen based on
that we cannot assume anything about the padding bits
when having a store that clobbers more memory than
indicated by the type of the value that is stored
(such as storing an i6 using an 8-bit store instruction).
Fixes: https://bugs.llvm.org/show_bug.cgi?id=41949
Reviewers: spatel, efriedma, fhahn
Reviewed By: efriedma
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62250
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@361605 91177308-0d34-0410-b5e6-96231b3b80d8
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358546 91177308-0d34-0410-b5e6-96231b3b80d8
Bug: https://bugs.llvm.org/show_bug.cgi?id=41175
In the bug test case the DSE pass is shortening the range of memory that a
memset is working on. A getelementptr is generated so that the new
starting address can be passed to memset. This instruction was not given
a DebugLoc.
To fix the bug, copy the DebugLoc from the memset instruction.
Patch by Orlando Cazalet-Hyams!
Differential Revision: https://reviews.llvm.org/D60556
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358270 91177308-0d34-0410-b5e6-96231b3b80d8
IntrArgMemOnly implies that only memory pointed to by pointer typed arguments will be accessed. But these intrinsics allow you to pass null to the pointer argument and put the full address into the index argument. Other passes won't be able to understand this.
A colleague found that ISPC was creating gathers like this and then dead store elimination removed some stores because it didn't understand what the gather was doing since the pointer argument was null.
Differential Revision: https://reviews.llvm.org/D58805
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355228 91177308-0d34-0410-b5e6-96231b3b80d8
This demonstrates dead store elimination removing a store that may alias a gather that uses null as its base.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355227 91177308-0d34-0410-b5e6-96231b3b80d8
Salvaging a redundant load instruction into a debug expression hides a
memory read from optimisation passes. Passes that alter memory behaviour
(such as LICM promoting memory to a register) aren't aware of these debug
memory reads and leave them unaltered, making the debug variable location
point somewhere unsafe.
Teaching passes to know about these debug memory reads would be challenging
and probably incomplete. Finding dbg.value instructions that need to be fixed
would likely be computationally expensive too, as more analysis would be
required. It's better to not generate debug-memory-reads instead, alas.
Changed tests:
* DeadStoreElim: test for salvaging of intermediate operations contributing
to the dead store, instead of salvaging of the redundant load,
* GVN: remove debuginfo behaviour checks completely, this behaviour is still
covered by other tests,
* InstCombine: don't test for salvaged loads, we're removing that behaviour.
Differential Revision: https://reviews.llvm.org/D57962
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353824 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Calls marked 'tail' cannot read or write allocas from the current frame
because the current frame might be destroyed by the time they run.
However, a tail call may use an alloca with byval. Calling with byval
copies the contents of the alloca into argument registers or stack
slots, so there is no lifetime issue. Tail calls never modify allocas,
so we can return just ModRefInfo::Ref.
Fixes PR38466, a longstanding bug.
Reviewers: hfinkel, nlewycky, gbiv, george.burgess.iv
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D50679
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339636 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This patch introduce new intrinsic -
strip.invariant.group that was described in the
RFC: Devirtualization v2
Reviewers: rsmith, hfinkel, nlopes, sanjoy, amharc, kuhar
Subscribers: arsenm, nhaehnle, JDevlieghere, hiraditya, xbolva00, llvm-commits
Differential Revision: https://reviews.llvm.org/D47103
Co-authored-by: Krzysztof Pszeniczny <krzysztof.pszeniczny@gmail.com>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336073 91177308-0d34-0410-b5e6-96231b3b80d8
Before this patch, debugify would insert debug value intrinsics before the
terminating instruction in a block. This had the advantage of being simple,
but was a bit too simple/unrealistic.
This patch teaches debugify to insert debug values immediately after their
operand defs. This enables better testing of the compiler.
For example, with this patch, `opt -debugify-each` is able to identify a
vectorizer DI-invariance bug fixed in llvm.org/PR32761. In this bug, the
vectorizer produced different output with/without debug info present.
Reverting Davide's bugfix locally, I see:
$ ~/scripts/opt-check-dbg-invar.sh ./bin/opt \
.../SLPVectorizer/AArch64/spillcost-di.ll -slp-vectorizer
Comparing: -slp-vectorizer .../SLPVectorizer/AArch64/spillcost-di.ll
Baseline: /var/folders/j8/t4w0bp8j6x1g6fpghkcb4sjm0000gp/T/tmp.iYYeL1kf
With DI : /var/folders/j8/t4w0bp8j6x1g6fpghkcb4sjm0000gp/T/tmp.sQtQSeet
9,11c9,11
< %5 = getelementptr inbounds %0, %0* %2, i64 %0, i32 1
< %6 = bitcast i64* %4 to <2 x i64>*
< %7 = load <2 x i64>, <2 x i64>* %6, align 8, !tbaa !0
---
> %5 = load i64, i64* %4, align 8, !tbaa !0
> %6 = getelementptr inbounds %0, %0* %2, i64 %0, i32 1
> %7 = load i64, i64* %6, align 8, !tbaa !5
12a13
> store i64 %5, i64* %8, align 8, !tbaa !0
14,15c15
< %10 = bitcast i64* %8 to <2 x i64>*
< store <2 x i64> %7, <2 x i64>* %10, align 8, !tbaa !0
---
> store i64 %7, i64* %9, align 8, !tbaa !5
:: Found a test case ^
Running this over the *.ll files in tree, I found four additional examples
which compile differently with/without DI present. I plan on filing bugs for
these.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334118 91177308-0d34-0410-b5e6-96231b3b80d8
Setting the "Debug Info Version" module flag makes it possible to pipe
synthetic debug info into llc, which is useful for testing backends.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333237 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This change teaches DSE that the atomic memory intrinsics can be overwriten
partially in the same way as the non-atomic forms. Specifically, that the
atomic memcpy & memset can be shortened at the end and that the atomic memset
can be shortened at the beginning, if they partially overwritten
by later stores.
Reviewers: mkazantsev, skatkov, apilipenko, efriedma, rsmith, spatel, filcab, sanjoy
Reviewed By: efriedma
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D45584
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331991 91177308-0d34-0410-b5e6-96231b3b80d8
In order to set breakpoints on labels and list source code around
labels, we need collect debug information for labels, i.e., label
name, the function label belong, line number in the file, and the
address label located. In order to keep these information in LLVM
IR and to allow backend to generate debug information correctly.
We create a new kind of metadata for labels, DILabel. The format
of DILabel is
!DILabel(scope: !1, name: "foo", file: !2, line: 3)
We hope to keep debug information as much as possible even the
code is optimized. So, we create a new kind of intrinsic for label
metadata to avoid the metadata is eliminated with basic block.
The intrinsic will keep existing if we keep it from optimized out.
The format of the intrinsic is
llvm.dbg.label(metadata !1)
It has only one argument, that is the DILabel metadata. The
intrinsic will follow the label immediately. Backend could get the
label metadata through the intrinsic's parameter.
We also create DIBuilder API for labels to be used by Frontend.
Frontend could use createLabel() to allocate DILabel objects, and use
insertLabel() to insert llvm.dbg.label intrinsic in LLVM IR.
Differential Revision: https://reviews.llvm.org/D45024
Patch by Hsiangkai Wang.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331841 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This change teaches DSE that the atomic memory intrinsics are stores
that can be eliminated, and can allow other stores to be eliminated.
This change specifically does not teach DSE that these intrinsics
can be partially eliminated (i.e. length reduced, and dest/src changed);
that will be handled in another change.
Reviewers: mkazantsev, skatkov, apilipenko, efriedma, rsmith
Reviewed By: efriedma
Subscribers: dmgreen, llvm-commits
Differential Revision: https://reviews.llvm.org/D45535
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330629 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
These tests show that DSE currently does nothing with the atomic memory
intrinsics. Future work will teach DSE how to simplify these.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329845 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
In preparation for a future commit, this regenerates the test checks for
test/Transforms/DeadStoreElimination/OverwriteStoreBegin.ll
test/Transforms/DeadStoreElimination/OverwriteStoreEnd.ll
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329839 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
In preparation for a future commit, this regenerates the test checks for
test/Transforms/DeadStoreElimination/simple.ll
test/Transforms/DeadStoreElimination/memintrinsics.ll
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@329824 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
We used to remove the first memmove in cases like this:
memmove(p, p+2, 8);
memmove(p, p+2, 8);
which is incorrect. Fix this by changing isPossibleSelfRead to what was most
likely the intended behavior.
Historical note: the buggy code was added in https://reviews.llvm.org/rL120974
to address PR8728.
Reviewers: rsmith
Subscribers: mcrosier, llvm-commits, jlebar
Differential Revision: https://reviews.llvm.org/D43425
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@325641 91177308-0d34-0410-b5e6-96231b3b80d8
According to `llvm-dwarfdump --statistics` this salvages 43 additional
unique source variables in a stage2 build of clang. It increases the
size of the .debug_loc section by 0.002% (or 2864 bytes).
Differential Revision: https://reviews.llvm.org/D43220
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@325035 91177308-0d34-0410-b5e6-96231b3b80d8
We can miscompile because we're not checking is the memory might
me modified between the seemingly redundant store ops.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@323704 91177308-0d34-0410-b5e6-96231b3b80d8
This patch implements Chandler's idea [0] for supporting languages that
require support for infinite loops with side effects, such as Rust, providing
part of a solution to bug 965 [1].
Specifically, it adds an `llvm.sideeffect()` intrinsic, which has no actual
effect, but which appears to optimization passes to have obscure side effects,
such that they don't optimize away loops containing it. It also teaches
several optimization passes to ignore this intrinsic, so that it doesn't
significantly impact optimization in most cases.
As discussed on llvm-dev [2], this patch is the first of two major parts.
The second part, to change LLVM's semantics to have defined behavior
on infinite loops by default, with a function attribute for opting into
potential-undefined-behavior, will be implemented and posted for review in
a separate patch.
[0] http://lists.llvm.org/pipermail/llvm-dev/2015-July/088103.html
[1] https://bugs.llvm.org/show_bug.cgi?id=965
[2] http://lists.llvm.org/pipermail/llvm-dev/2017-October/118632.html
Differential Revision: https://reviews.llvm.org/D38336
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317729 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Memory dependence analysis no longer counts DbgInfoIntrinsics towards the
limit where to abort the analysis. Before, a bunch of calls to dbg.value
could affect the generated code, meaning that with -g we could generate
different code than without.
Reviewers: chandlerc, Prazek, davide, efriedma
Reviewed By: efriedma
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D39181
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@316551 91177308-0d34-0410-b5e6-96231b3b80d8
This is a 2nd attempt at:
https://reviews.llvm.org/rL310055
...which was reverted at rL310123 because of PR34074:
https://bugs.llvm.org/show_bug.cgi?id=34074
In this version, we break out of the inner loop after we successfully merge and kill a pair of stores. In the
earlier rev, we were continuing instead, which meant we could process the invalid info from a now dead store.
Original commit message (authored by Filipe Cabecinhas):
This fixes PR31777.
If both stores' values are ConstantInt, we merge the two stores
(shifting the smaller store appropriately) and replace the earlier (and
larger) store with an updated constant.
In the future we should also support vectors of integers. And maybe
float/double if we can.
Differential Revision: https://reviews.llvm.org/D30703
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314206 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This fixes PR31777.
If both stores' values are ConstantInt, we merge the two stores
(shifting the smaller store appropriately) and replace the earlier (and
larger) store with an updated constant.
In the future we should also support vectors of integers. And maybe
float/double if we can.
Reviewers: hfinkel, junbuml, jfb, RKSimon, bkramer
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D30703
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310055 91177308-0d34-0410-b5e6-96231b3b80d8
There is no situation where this rarely-used argument cannot be
substituted with a DIExpression and removing it allows us to simplify
the DWARF backend. Note that this patch does not yet remove any of
the newly dead code.
rdar://problem/33580047
Differential Revision: https://reviews.llvm.org/D35951
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309426 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
We teach alias analysis that invariant.start is readonly.
This helps with GVN and memcopy optimizations that currently treat.
invariant.start as a clobber.
We need to treat this as readonly, so that DSE does not incorrectly
remove stores prior to the invariant.start
Reviewers: sanjoy, reames, majnemer, dberlin
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D23214
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278138 91177308-0d34-0410-b5e6-96231b3b80d8
Recommiting r275571 after fixing crash reported in PR28270.
Now we erase elements of IOL in deleteDeadInstruction().
Original Summary:
This change use the overlap interval map built from partial overwrite tracking to perform shortening MemIntrinsics.
Add test cases which was missing opportunities before.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276452 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This change use the overlap interval map built from partial overwrite tracking to perform shortening MemIntrinsics.
Add test cases which was missing opportunities before.
Reviewers: hfinkel, eeckstein, mcrosier
Subscribers: mcrosier, llvm-commits
Differential Revision: https://reviews.llvm.org/D21909
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275571 91177308-0d34-0410-b5e6-96231b3b80d8
The dse_with_dbg_value.ll test committed with r273141 is removed because this
we no longer performs any type of back tracking, which is what was causing the
codegen differences with and without debug information.
Differential Revision: http://reviews.llvm.org/D21613
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274660 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Found cases where DSE incorrectly add partially-overwritten intervals.
Please see the test case for details.
Reviewers: mcrosier, eeckstein, hfinkel
Subscribers: mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D21859
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274237 91177308-0d34-0410-b5e6-96231b3b80d8
DeadStoreElimination can currently remove a small store rendered unnecessary by
a later larger one, but could not remove a larger store rendered unnecessary by
a series of later smaller ones. This adds that capability.
It works by keeping a map, which is used as an effective interval map, for each
store later overwritten only partially, and filling in that interval map as
more such stores are discovered. No additional walking or aliasing queries are
used. In the map forms an interval covering the the entire earlier store, then
it is dead and can be removed. The map is used as an interval map by storing a
mapping between the ending offset and the beginning offset of each interval.
I discovered this problem when investigating a performance issue with code like
this on PowerPC:
#include <complex>
using namespace std;
complex<float> bar(complex<float> C);
complex<float> foo(complex<float> C) {
return bar(C)*C;
}
which produces this:
define void @_Z4testSt7complexIfE(%"struct.std::complex"* noalias nocapture sret %agg.result, i64 %c.coerce) {
entry:
%ref.tmp = alloca i64, align 8
%tmpcast = bitcast i64* %ref.tmp to %"struct.std::complex"*
%c.sroa.0.0.extract.shift = lshr i64 %c.coerce, 32
%c.sroa.0.0.extract.trunc = trunc i64 %c.sroa.0.0.extract.shift to i32
%0 = bitcast i32 %c.sroa.0.0.extract.trunc to float
%c.sroa.2.0.extract.trunc = trunc i64 %c.coerce to i32
%1 = bitcast i32 %c.sroa.2.0.extract.trunc to float
call void @_Z3barSt7complexIfE(%"struct.std::complex"* nonnull sret %tmpcast, i64 %c.coerce)
%2 = bitcast %"struct.std::complex"* %agg.result to i64*
%3 = load i64, i64* %ref.tmp, align 8
store i64 %3, i64* %2, align 4 ; <--- ***** THIS SHOULD NOT BE HERE ****
%_M_value.realp.i.i = getelementptr inbounds %"struct.std::complex", %"struct.std::complex"* %agg.result, i64 0, i32 0, i32 0
%4 = lshr i64 %3, 32
%5 = trunc i64 %4 to i32
%6 = bitcast i32 %5 to float
%_M_value.imagp.i.i = getelementptr inbounds %"struct.std::complex", %"struct.std::complex"* %agg.result, i64 0, i32 0, i32 1
%7 = trunc i64 %3 to i32
%8 = bitcast i32 %7 to float
%mul_ad.i.i = fmul fast float %6, %1
%mul_bc.i.i = fmul fast float %8, %0
%mul_i.i.i = fadd fast float %mul_ad.i.i, %mul_bc.i.i
%mul_ac.i.i = fmul fast float %6, %0
%mul_bd.i.i = fmul fast float %8, %1
%mul_r.i.i = fsub fast float %mul_ac.i.i, %mul_bd.i.i
store float %mul_r.i.i, float* %_M_value.realp.i.i, align 4
store float %mul_i.i.i, float* %_M_value.imagp.i.i, align 4
ret void
}
the problem here is not just that the i64 store is unnecessary, but also that
it blocks further backend optimizations of the other uses of that i64 value in
the backend.
In the future, we might want to add a special case for handling smaller
accesses (e.g. using a bit vector) if the map mechanism turns out to be
noticeably inefficient. A sorted vector is also a possible replacement for the
map for small numbers of tracked intervals.
Differential Revision: http://reviews.llvm.org/D18586
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273559 91177308-0d34-0410-b5e6-96231b3b80d8
After a store has been eliminated, when making sure that the
instruction iterator points to a valid instruction, dbg intrinsics are
now ignored as a new instruction.
Patch by Henric Karlsson.
Reviewed by Daniel Berlin.
Differential Revision: http://reviews.llvm.org/D21076
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273141 91177308-0d34-0410-b5e6-96231b3b80d8
In rL272580 I accidentally added a test case to test/CodeGen when
test/Transforms/DeadStoreElimination/ is a better place for it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272581 91177308-0d34-0410-b5e6-96231b3b80d8
Summary: This change will shorten memset if the beginning of memset is overwritten by later stores.
Reviewers: hfinkel, eeckstein, dberlin, mcrosier
Subscribers: mgrang, mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D18906
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267197 91177308-0d34-0410-b5e6-96231b3b80d8
Currently each Function points to a DISubprogram and DISubprogram has a
scope field. For member functions the scope is a DICompositeType. DIScopes
point to the DICompileUnit to facilitate type uniquing.
Distinct DISubprograms (with isDefinition: true) are not part of the type
hierarchy and cannot be uniqued. This change removes the subprograms
list from DICompileUnit and instead adds a pointer to the owning compile
unit to distinct DISubprograms. This would make it easy for ThinLTO to
strip unneeded DISubprograms and their transitively referenced debug info.
Motivation
----------
Materializing DISubprograms is currently the most expensive operation when
doing a ThinLTO build of clang.
We want the DISubprogram to be stored in a separate Bitcode block (or the
same block as the function body) so we can avoid having to expensively
deserialize all DISubprograms together with the global metadata. If a
function has been inlined into another subprogram we need to store a
reference the block containing the inlined subprogram.
Attached to https://llvm.org/bugs/show_bug.cgi?id=27284 is a python script
that updates LLVM IR testcases to the new format.
http://reviews.llvm.org/D19034
<rdar://problem/25256815>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266446 91177308-0d34-0410-b5e6-96231b3b80d8
This mostly cosmetic patch moves the DebugEmissionKind enum from DIBuilder
into DICompileUnit. DIBuilder is not the right place for this enum to live
in — a metadata consumer should not have to include DIBuilder.h.
I also added a Verifier check that checks that the emission kind of a
DICompileUnit is actually legal.
http://reviews.llvm.org/D18612
<rdar://problem/25427165>
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265077 91177308-0d34-0410-b5e6-96231b3b80d8
A release fence acts as a publication barrier for stores within the current thread to become visible to other threads which might observe the release fence. It does not require the current thread to observe stores performed on other threads. As a result, we can allow store-load and load-load forwarding across a release fence.
We choose to be much more conservative about stores. In theory, nothing prevents us from shifting a store from after a release fence to before it, and then eliminating the preceeding (previously fenced) store. Doing this without actually moving the second store is likely also legal, but we chose to be conservative at this time.
The LangRef indicates only atomic loads and stores are effected by fences. This patch chooses to be far more conservative then that.
This is the GVN companion to http://reviews.llvm.org/D11434 which applied the same logic in EarlyCSE and has been baking in tree for a while now.
Differential Revision: http://reviews.llvm.org/D11436
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264472 91177308-0d34-0410-b5e6-96231b3b80d8
Hideto Ueno