Commit Graph

114 Commits

Author SHA1 Message Date
Ulrich Weigand 5f4373a2fc [SystemZ] Do not crash when selecting an OR of two constants
In rare cases, common code will attempt to select an OR of two
constants.  This confuses the logic in splitLargeImmediate,
causing an internal error during isel.  Fixed by simply leaving
this case to common code to handle.

This fixes PR34859.

llvm-svn: 318187
2017-11-14 20:00:34 +00:00
Ulrich Weigand 55b8590e03 [SystemZ] Fix invalid codegen using RISBMux on out-of-range bits
Before using the 32-bit RISBMux set of instructions we need to
verify that the input bits are actually within range of the 32-bit
instruction.  This fixer PR35289.

llvm-svn: 318177
2017-11-14 19:20:46 +00:00
Ulrich Weigand d39e9dca1b [SystemZ] Add support for the "o" inline asm constraint
We don't really need any special handling of "offsettable"
memory addresses, but since some existing code uses inline
asm statements with the "o" constraint, add support for this
constraint for compatibility purposes.

llvm-svn: 317807
2017-11-09 16:31:57 +00:00
Craig Topper d0af7e8ab8 [SelectionDAG] Use KnownBits struct in DAG's computeKnownBits and simplifyDemandedBits
This patch replaces the separate APInts for KnownZero/KnownOne with a single KnownBits struct. This is similar to what was done to ValueTracking's version recently.

This is largely a mechanical transformation from KnownZero to Known.Zero.

Differential Revision: https://reviews.llvm.org/D32569

llvm-svn: 301620
2017-04-28 05:31:46 +00:00
Ulrich Weigand 524f276c74 [SystemZ] Improve use of conditional instructions
This patch moves formation of LOC-type instructions from (late)
IfConversion to the early if-conversion pass, and in some cases
additionally creates them directly from select instructions
during DAG instruction selection.

To make early if-conversion work, the patch implements the
canInsertSelect / insertSelect callbacks.  It also implements
the commuteInstructionImpl and FoldImmediate callbacks to
enable generation of the full range of LOC instructions.

Finally, the patch adds support for all instructions of the
load-store-on-condition-2 facility, which allows using LOC
instructions also for high registers.

Due to the use of the GRX32 register class to enable high registers,
we now also have to handle the cases where there are still no single
hardware instructions (conditional move from a low register to a high
register or vice versa).  These are converted back to a branch sequence
after register allocation.  Since the expandRAPseudos callback is not
allowed to create new basic blocks, this requires a simple new pass,
modelled after the ARM/AArch64 ExpandPseudos pass.

Overall, this patch causes significantly more LOC-type instructions
to be used, and results in a measurable performance improvement.

llvm-svn: 288028
2016-11-28 13:34:08 +00:00
Ulrich Weigand 92c2c672e5 [SystemZ] Support load-and-zero-rightmost-byte facility
This adds support for the LZRF/LZRG/LLZRGF instructions that were
added on z13, and uses them for code generation were appropriate.

SystemZDAGToDAGISel::tryRISBGZero is updated again to prefer LLZRGF
over RISBG where both would be possible.

llvm-svn: 286586
2016-11-11 12:46:28 +00:00
Ulrich Weigand 5dc7b67c62 [SystemZ] Use LLGT(R) instructions
This adds support for the 31-to-64-bit zero extension instructions
LLGT and LLGTR and uses them for code generation where appropriate.

Since this operation can also be performed via RISBG, we have to
update SystemZDAGToDAGISel::tryRISBGZero so that we prefer LLGT
over RISBG in case both are possible.  The patch includes some
simplification to the tryRISBGZero code; this is not intended
to cause any (further) functional change in codegen.

llvm-svn: 286585
2016-11-11 12:43:51 +00:00
Mehdi Amini 117296c0a0 Use StringRef in Pass/PassManager APIs (NFC)
llvm-svn: 283004
2016-10-01 02:56:57 +00:00
Sanjay Patel 1ed771f5d7 getVectorElementType().getSizeInBits() -> getScalarSizeInBits() ; NFCI
llvm-svn: 281495
2016-09-14 16:37:15 +00:00
Sanjay Patel b1f0a0f4a8 getValueType().getSizeInBits() -> getValueSizeInBits() ; NFCI
llvm-svn: 281493
2016-09-14 16:05:51 +00:00
Justin Lebar adbf09e8cf [CodeGen] Split out the notions of MI invariance and MI dereferenceability.
Summary:
An IR load can be invariant, dereferenceable, neither, or both.  But
currently, MI's notion of invariance is IR-invariant &&
IR-dereferenceable.

This patch splits up the notions of invariance and dereferenceability at
the MI level.  It's NFC, so adds some probably-unnecessary
"is-dereferenceable" checks, which we can remove later if desired.

Reviewers: chandlerc, tstellarAMD

Subscribers: jholewinski, arsenm, nemanjai, llvm-commits

Differential Revision: https://reviews.llvm.org/D23371

llvm-svn: 281151
2016-09-11 01:38:58 +00:00
Zhan Jun Liau cf2f4b3251 [SystemZ] Use valid base/index regs for inline asm
Summary:
Inline asm memory constraints can have the base or index register be assigned
to %r0 right now. Make sure that we assign only ADDR64 registers to the base
and index.

Reviewers: uweigand

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D23367

llvm-svn: 279157
2016-08-18 21:44:15 +00:00
Justin Bogner cd1d5aaf2e Replace a few more "fall through" comments with LLVM_FALLTHROUGH
Follow up to r278902. I had missed "fall through", with a space.

llvm-svn: 278970
2016-08-17 20:30:52 +00:00
Zhan Jun Liau 0df350589f [SystemZ] Recognize RISBG opportunities involving a truncate
Summary:
Recognize RISBG opportunities where the end result is narrower than the
original input - where a truncate separates the shift/and operations.

The motivating case is some code in postgres which looks like:

	srlg	%r2, %r0, 11
	nilh	%r2, 255

Reviewers: uweigand

Author: RolandF

Differential Revision: http://reviews.llvm.org/D21452

llvm-svn: 273433
2016-06-22 16:16:27 +00:00
Ulrich Weigand daae87aa21 [SystemZ] Enable index register memory constraints for inline ASM
This enables use of the 'R' and 'T' memory constraints for inline ASM
operands on SystemZ, which allow an index register as well as an
immediate displacement. This patch includes corresponding documentation
and test case updates.

As with the last patch of this kind, I moved the 'm' constraint to the
most general case, which is now 'T' (base + 20-bit signed displacement +
index register).

Author: colpell
Differential Revision: http://reviews.llvm.org/D21239

llvm-svn: 272547
2016-06-13 14:24:05 +00:00
Benjamin Kramer bdc4956bac Pass DebugLoc and SDLoc by const ref.
This used to be free, copying and moving DebugLocs became expensive
after the metadata rewrite. Passing by reference eliminates a ton of
track/untrack operations. No functionality change intended.

llvm-svn: 272512
2016-06-12 15:39:02 +00:00
Ulrich Weigand 79564611d9 [SystemZ] Enable long displacement constraints for inline ASM operands
This enables use of the 'S' constraint for inline ASM operands on
SystemZ, which allows for a memory reference with a signed 20-bit
immediate displacement. This patch includes corresponding documentation
and test case updates.

I've changed the 'T' constraint to match the new behavior for 'S', as
'T' also uses a long displacement (though index constraints are still
not implemented). I also changed 'm' to match the behavior for 'S' as
this will allow for a wider range of displacements for 'm', though
correct me if that's not the right decision.

Author: colpell
Differential Revision: http://reviews.llvm.org/D21097

llvm-svn: 272266
2016-06-09 15:19:16 +00:00
Justin Bogner 9b34e8a770 SDAG: Implement Select instead of SelectImpl in SystemZDAGToDAGISel
- Where we were returning a node before, call ReplaceNode instead.
- Where we would return null to fall back to another selector, rename
  the method to try* and return a bool for success.

Part of llvm.org/pr26808.

llvm-svn: 269505
2016-05-13 22:42:08 +00:00
Justin Bogner bbcd2233b2 SDAG: Avoid relying on the return value of SelectCode in SystemZ. NFC
This is a bit of a spot fix for now. I'll try to fix this up more
comprehensively soon.

This is part of the work to have Select return void instead of an
SDNode *, which is in turn part of llvm.org/pr26808.

llvm-svn: 269120
2016-05-10 21:11:26 +00:00
Justin Bogner ffb273d21a SDAG: Stop relying on Select's return value in SystemZ's splitLargeImmediate. NFC
The call to Select on Upper here happens in an unusual order in order
to defeat the constant folding that getNode() does. Add a comment
explaining why we can't just move the Select to later to avoid a
Handle, and wrap the call to SelectCode in a handle so we don't need
its return value.

This is part of the work to have Select return void instead of an
SDNode *, which is in turn part of llvm.org/pr26808.

llvm-svn: 268990
2016-05-09 23:54:23 +00:00
Justin Bogner b012699741 SDAG: Rename Select->SelectImpl and repurpose Select as returning void
This is a step towards removing the rampant undefined behaviour in
SelectionDAG, which is a part of llvm.org/PR26808.

We rename SelectionDAGISel::Select to SelectImpl and update targets to
match, and then change Select to return void and consolidate the
sketchy behaviour we're trying to get away from there.

Next, we'll update backends to implement `void Select(...)` instead of
SelectImpl and eventually drop the base Select implementation.

llvm-svn: 268693
2016-05-05 23:19:08 +00:00
Marcin Koscielnicki 9de88d9bbe [SystemZ] Implement llvm.get.dynamic.area.offset
To be used for AddressSanitizer.

Differential Revision: http://reviews.llvm.org/D19817

llvm-svn: 268572
2016-05-04 23:31:26 +00:00
Duncan P. N. Exon Smith a2c90e4743 SystemZ: Remove implicit ilist iterator conversion, NFC
llvm-svn: 250790
2015-10-20 01:12:46 +00:00
Simon Pilgrim 0750c84623 [DAGCombiner] Attempt to mask vectors before zero extension instead of after.
For cases where we TRUNCATE and then ZERO_EXTEND to a larger size (often from vector legalization), see if we can mask the source data and then ZERO_EXTEND (instead of after a ANY_EXTEND). This can help avoid having to generate a larger mask, and possibly applying it to several sub-vectors.

(zext (truncate x)) -> (zext (and(x, m))

Includes a minor patch to SystemZ to better recognise 8/16-bit zero extension patterns from RISBG bit-extraction code.

This is the first of a number of minor patches to help improve the conversion of byte masks to clear mask shuffles.

Differential Revision: http://reviews.llvm.org/D11764

llvm-svn: 245160
2015-08-15 13:27:30 +00:00
Ulrich Weigand 77884bcb5d [SystemZ] Only attempt RxSBG optimization for integer types
As pointed out by Justin Bogner (see r240520), SystemZDAGToDAGISel::Select
currently attempts to convert boolean operations into RxSBG even on some
non-integer types (in particular, vector types).  This would not work in
any case, and it happened to trigger undefined behaviour in allOnes.

This patch verifies that we have a (<= 64-bit) integer type before
attempting to perform this optimization.

llvm-svn: 240634
2015-06-25 11:52:36 +00:00
Justin Bogner c97c48aadc SystemZ: Rephrase this allOnes calculation to avoid UB
This allOnes function hits undefined behaviour if Count is greater
than 64, but we can avoid that and simplify the calculation by just
saturating if such a value is passed in.

This comes up under ubsan becauseRxSBGOperands is sometimes created
with values that are 128 bits wide. Somebody more familiar with this
code should probably look into whether that's expected, as a 64 bit
mask may or may not be appropriate for such types.

llvm-svn: 240520
2015-06-24 05:59:19 +00:00
Chandler Carruth ac80dc7532 [PM/AA] Remove the Location typedef from the AliasAnalysis class now
that it is its own entity in the form of MemoryLocation, and update all
the callers.

This is an entirely mechanical change. References to "Location" within
AA subclases become "MemoryLocation", and elsewhere
"AliasAnalysis::Location" becomes "MemoryLocation". Hope that helps
out-of-tree folks update.

llvm-svn: 239885
2015-06-17 07:18:54 +00:00
Ulrich Weigand ce4c109585 [SystemZ] Add CodeGen support for integer vector types
This the first of a series of patches to add CodeGen support exploiting
the instructions of the z13 vector facility.  This patch adds support
for the native integer vector types (v16i8, v8i16, v4i32, v2i64).

When the vector facility is present, we default to the new vector ABI.
This is characterized by two major differences:
- Vector types are passed/returned in vector registers
  (except for unnamed arguments of a variable-argument list function).
- Vector types are at most 8-byte aligned.

The reason for the choice of 8-byte vector alignment is that the hardware
is able to efficiently load vectors at 8-byte alignment, and the ABI only
guarantees 8-byte alignment of the stack pointer, so requiring any higher
alignment for vectors would require dynamic stack re-alignment code.

However, for compatibility with old code that may use vector types, when
*not* using the vector facility, the old alignment rules (vector types
are naturally aligned) remain in use.

These alignment rules are not only implemented at the C language level
(implemented in clang), but also at the LLVM IR level.  This is done
by selecting a different DataLayout string depending on whether the
vector ABI is in effect or not.

Based on a patch by Richard Sandiford.

llvm-svn: 236521
2015-05-05 19:25:42 +00:00
Sergey Dmitrouk 842a51bad8 Reapply r235977 "[DebugInfo] Add debug locations to constant SD nodes"
[DebugInfo] Add debug locations to constant SD nodes

This adds debug location to constant nodes of Selection DAG and updates
all places that create constants to pass debug locations
(see PR13269).

Can't guarantee that all locations are correct, but in a lot of cases choice
is obvious, so most of them should be. At least all tests pass.

Tests for these changes do not cover everything, instead just check it for
SDNodes, ARM and AArch64 where it's easy to get incorrect locations on
constants.

This is not complete fix as FastISel contains workaround for wrong debug
locations, which drops locations from instructions on processing constants,
but there isn't currently a way to use debug locations from constants there
as llvm::Constant doesn't cache it (yet). Although this is a bit different
issue, not directly related to these changes.

Differential Revision: http://reviews.llvm.org/D9084

llvm-svn: 235989
2015-04-28 14:05:47 +00:00
Daniel Jasper 48e93f7181 Revert "[DebugInfo] Add debug locations to constant SD nodes"
This breaks a test:
http://bb.pgr.jp/builders/cmake-llvm-x86_64-linux/builds/23870

llvm-svn: 235987
2015-04-28 13:38:35 +00:00
Sergey Dmitrouk adb4c69d5c [DebugInfo] Add debug locations to constant SD nodes
This adds debug location to constant nodes of Selection DAG and updates
all places that create constants to pass debug locations
(see PR13269).

Can't guarantee that all locations are correct, but in a lot of cases choice
is obvious, so most of them should be. At least all tests pass.

Tests for these changes do not cover everything, instead just check it for
SDNodes, ARM and AArch64 where it's easy to get incorrect locations on
constants.

This is not complete fix as FastISel contains workaround for wrong debug
locations, which drops locations from instructions on processing constants,
but there isn't currently a way to use debug locations from constants there
as llvm::Constant doesn't cache it (yet). Although this is a bit different
issue, not directly related to these changes.

Differential Revision: http://reviews.llvm.org/D9084

llvm-svn: 235977
2015-04-28 11:56:37 +00:00
Ulrich Weigand 371d10a4eb [SystemZ] Support RISBGN instruction on zEC12
So far, we do not yet support any instruction specific to zEC12.
Most of the facilities added with zEC12 are indeed not very useful
to compiler code generation, but there is one exception: the
miscellaneous-extensions facility provides the RISBGN instruction,
which is a variant of RISBG that does not set the condition code.

Add support for this facility, MC support for RISBGN, and CodeGen
support for prefering RISBGN over RISBG on zEC12, unless we can
actually make use of the condition code set by RISBG.

llvm-svn: 233690
2015-03-31 12:58:17 +00:00
Daniel Sanders 2eeace219d [systemz] Distinguish the 'Q', 'R', 'S', and 'T' inline assembly memory constraints.
Summary:
But still handle them the same way since I don't know how they differ on
this target.

No functional change intended.

Reviewers: uweigand

Reviewed By: uweigand

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8251

llvm-svn: 232495
2015-03-17 16:16:14 +00:00
Daniel Sanders 60f1db0525 Recommit r232027 with PR22883 fixed: Add infrastructure for support of multiple memory constraints.
The operand flag word for ISD::INLINEASM nodes now contains a 15-bit
memory constraint ID when the operand kind is Kind_Mem. This constraint
ID is a numeric equivalent to the constraint code string and is converted
with a target specific hook in TargetLowering.

This patch maps all memory constraints to InlineAsm::Constraint_m so there
is no functional change at this point. It just proves that using these
previously unused bits in the encoding of the flag word doesn't break
anything.

The next patch will make each target preserve the current mapping of
everything to Constraint_m for itself while changing the target independent
implementation of the hook to return Constraint_Unknown appropriately. Each
target will then be adapted in separate patches to use appropriate
Constraint_* values.

PR22883 was caused the matching operands copying the whole of the operand flags
for the matched operand. This included the constraint id which needed to be
replaced with the operand number. This has been fixed with a conversion
function. Following on from this, matching operands also used the operand
number as the constraint id. This has been fixed by looking up the matched
operand and taking it from there. 

llvm-svn: 232165
2015-03-13 12:45:09 +00:00
Hal Finkel e78e52ba9b Revert "r232027 - Add infrastructure for support of multiple memory constraints"
This (r232027) has caused PR22883; so it seems those bits might be used by
something else after all. Reverting until we can figure out what else to do.

Original commit message:

The operand flag word for ISD::INLINEASM nodes now contains a 15-bit
memory constraint ID when the operand kind is Kind_Mem. This constraint
ID is a numeric equivalent to the constraint code string and is converted
with a target specific hook in TargetLowering.

This patch maps all memory constraints to InlineAsm::Constraint_m so there
is no functional change at this point. It just proves that using these
previously unused bits in the encoding of the flag word doesn't break anything.

The next patch will make each target preserve the current mapping of
everything to Constraint_m for itself while changing the target independent
implementation of the hook to return Constraint_Unknown appropriately. Each
target will then be adapted in separate patches to use appropriate Constraint_*
values.

llvm-svn: 232093
2015-03-12 20:09:39 +00:00
Daniel Sanders 41c072e63b Add infrastructure for support of multiple memory constraints.
Summary:
The operand flag word for ISD::INLINEASM nodes now contains a 15-bit
memory constraint ID when the operand kind is Kind_Mem. This constraint
ID is a numeric equivalent to the constraint code string and is converted
with a target specific hook in TargetLowering.

This patch maps all memory constraints to InlineAsm::Constraint_m so there
is no functional change at this point. It just proves that using these
previously unused bits in the encoding of the flag word doesn't break anything.

The next patch will make each target preserve the current mapping of
everything to Constraint_m for itself while changing the target independent
implementation of the hook to return Constraint_Unknown appropriately. Each
target will then be adapted in separate patches to use appropriate Constraint_*
values.

Reviewers: hfinkel

Reviewed By: hfinkel

Subscribers: hfinkel, jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D8171

llvm-svn: 232027
2015-03-12 11:00:48 +00:00
Eric Christopher a6734178a7 Reuse a bunch of cached subtargets and remove getSubtarget calls
without a Function argument.

llvm-svn: 227647
2015-01-31 00:06:45 +00:00
Eric Christopher d913448b38 Remove the TargetMachine forwards for TargetSubtargetInfo based
information and update all callers. No functional change.

llvm-svn: 214781
2014-08-04 21:25:23 +00:00
Hal Finkel cc39b67530 AA metadata refactoring (introduce AAMDNodes)
In order to enable the preservation of noalias function parameter information
after inlining, and the representation of block-level __restrict__ pointer
information (etc.), additional kinds of aliasing metadata will be introduced.
This metadata needs to be carried around in AliasAnalysis::Location objects
(and MMOs at the SDAG level), and so we need to generalize the current scheme
(which is hard-coded to just one TBAA MDNode*).

This commit introduces only the necessary refactoring to allow for the
introduction of other aliasing metadata types, but does not actually introduce
any (that will come in a follow-up commit). What it does introduce is a new
AAMDNodes structure to hold all of the aliasing metadata nodes associated with
a particular memory-accessing instruction, and uses that structure instead of
the raw MDNode* in AliasAnalysis::Location, etc.

No functionality change intended.

llvm-svn: 213859
2014-07-24 12:16:19 +00:00
Jay Foad a0653a3e6c Rename ComputeMaskedBits to computeKnownBits. "Masked" has been
inappropriate since it lost its Mask parameter in r154011.

llvm-svn: 208811
2014-05-14 21:14:37 +00:00
Craig Topper 062a2baef0 [C++] Use 'nullptr'. Target edition.
llvm-svn: 207197
2014-04-25 05:30:21 +00:00
Chandler Carruth e96dd8975f [Modules] Make Support/Debug.h modular. This requires it to not change
behavior based on other files defining DEBUG_TYPE, which means it cannot
define DEBUG_TYPE at all. This is actually better IMO as it forces folks
to define relevant DEBUG_TYPEs for their files. However, it requires all
files that currently use DEBUG(...) to define a DEBUG_TYPE if they don't
already. I've updated all such files in LLVM and will do the same for
other upstream projects.

This still leaves one important change in how LLVM uses the DEBUG_TYPE
macro going forward: we need to only define the macro *after* header
files have been #include-ed. Previously, this wasn't possible because
Debug.h required the macro to be pre-defined. This commit removes that.
By defining DEBUG_TYPE after the includes two things are fixed:

- Header files that need to provide a DEBUG_TYPE for some inline code
  can do so by defining the macro before their inline code and undef-ing
  it afterward so the macro does not escape.

- We no longer have rampant ODR violations due to including headers with
  different DEBUG_TYPE definitions. This may be mostly an academic
  violation today, but with modules these types of violations are easy
  to check for and potentially very relevant.

Where necessary to suppor headers with DEBUG_TYPE, I have moved the
definitions below the includes in this commit. I plan to move the rest
of the DEBUG_TYPE macros in LLVM in subsequent commits; this one is big
enough.

The comments in Debug.h, which were hilariously out of date already,
have been updated to reflect the recommended practice going forward.

llvm-svn: 206822
2014-04-21 22:55:11 +00:00
Nick Lewycky aad475b324 Break PseudoSourceValue out of the Value hierarchy. It is now the root of its own tree containing FixedStackPseudoSourceValue (which you can use isa/dyn_cast on) and MipsCallEntry (which you can't). Anything that needs to use either a PseudoSourceValue* and Value* is strongly encouraged to use a MachinePointerInfo instead.
llvm-svn: 206255
2014-04-15 07:22:52 +00:00
Richard Sandiford b4d67b593e [SystemZ] Remove "virtual" from override methods
Also fix a couple of cases where "override" was missing.  No behavioural
change intended.

llvm-svn: 203110
2014-03-06 12:03:36 +00:00
Richard Sandiford 21f5d68a17 [SystemZ] Use "auto" for cast results
No functional change intended.

llvm-svn: 203106
2014-03-06 11:22:58 +00:00
Craig Topper 73156025e0 Switch all uses of LLVM_OVERRIDE to just use 'override' directly.
llvm-svn: 202621
2014-03-02 09:09:27 +00:00
Richard Sandiford 3875cb60f3 [SystemZ] Fix RNSBG bug introduced by r197802
The zext handling added in r197802 wasn't right for RNSBG.  This patch
restricts it to ROSBG, RXSBG and RISBG.  (The tests for RISBG were added
in r197802 since RISBG was the motivating example.)

llvm-svn: 198862
2014-01-09 11:28:53 +00:00
Richard Sandiford 41350a52ca [SystemZ] Use interlocked-access 1 instructions for CodeGen
...namely LOAD AND ADD, LOAD AND AND, LOAD AND OR and LOAD AND EXCLUSIVE OR.
LOAD AND ADD LOGICAL isn't really separately useful for LLVM.

I'll look at adding reusing the CC results in new year.

llvm-svn: 197985
2013-12-24 15:18:04 +00:00
Richard Sandiford 220ee49bce [SystemZ] Extend RISBG optimization
The handling of ANY_EXTEND and ZERO_EXTEND was too strict.  In this context
we can treat ZERO_EXTEND in much the same way as an AND and then also handle
outermost ZERO_EXTENDs.

I couldn't find a test that benefited from the ANY_EXTEND change, but it's
more obvious to write it this way once SIGN_EXTEND and ZERO_EXTEND are
handled differently.

llvm-svn: 197802
2013-12-20 11:49:48 +00:00
Richard Sandiford dd7dd930d1 [SystemZ] Fix incorrect use of RISBG for a zero-extended right shift
We would wrongly transform the testcase into the equivalent of an AND with 1.
The problem was that, when testing whether the shifted-in bits of the right
shift were significant, we used the width of the final zero-extended result
rather than the width of the shifted value.

llvm-svn: 195731
2013-11-26 10:53:16 +00:00