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2019-08-19Refactor isPointerOffset (NFC).Evgeniy Stepanov1-24/+19
Summary: Simplify the API using Optional<> and address comments in https://reviews.llvm.org/D66165 Reviewers: vitalybuka Subscribers: hiraditya, llvm-commits, ostannard, pcc Tags: #llvm Differential Revision: https://reviews.llvm.org/D66317 llvm-svn: 369300
2019-08-16[ValueTracking] Fix recurrence detection to check both PHI operands.Florian Hahn1-1/+1
Summary: Currently we fail to compute known bits for recurrences where the first incoming value is the start value of the recurrence. Instead of exiting the loop when the first incoming value is not the step of the recurrence, continue to check the second incoming value. The original code uses a loop to handle both cases, but incorrectly exits instead of continuing. Reviewers: lebedev.ri, spatel, nikic Reviewed By: lebedev.ri Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D66216 llvm-svn: 369088
2019-08-15Move isPointerOffset function to ValueTracking (NFC).Evgeniy Stepanov1-0/+83
Summary: To be reused in MemTag sanitizer. Reviewers: pcc, vitalybuka, ostannard Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D66165 llvm-svn: 369062
2019-08-15[ValueTracking] Look through ptrmask intrinsics during getUnderlyingObject.Florian Hahn1-2/+4
Reviewers: nlopes, efriedma, hfinkel, sanjoy, aqjune, jdoerfert Reviewed By: jdoerfert Subscribers: jdoerfert, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D61669 llvm-svn: 369036
2019-08-15[ValueTracking] Add MustPreserveNullness arg to functions analyzing calls. (NFC)Florian Hahn1-5/+8
Some uses of getArgumentAliasingToReturnedPointer and isIntrinsicReturningPointerAliasingArgumentWithoutCapturing require the calls/intrinsics to preserve the nullness of the argument. For alias analysis, the nullness property does not really come into play. This patch explicitly sets it to true. In D61669, the alias analysis uses will be switched to not require preserving nullness. Reviewers: nlopes, efriedma, hfinkel, sanjoy, aqjune, jdoerfert Reviewed By: jdoerfert Tags: #llvm Differential Revision: https://reviews.llvm.org/D64150 llvm-svn: 368993
2019-08-13[ValueTracking] Improve reverse assumption inferenceNikita Popov1-1/+7
Use isGuaranteedToTransferExecutionToSuccessor() instead of isSafeToSpeculativelyExecute() when seeing whether we can propagate the information in an assume backwards in isValidAssumeForContext(). The latter is more general - it also allows arbitrary loads/stores - and is also the condition we want: if our assume is guaranteed to execute, its condition not holding would be UB. Original patch by arielb1. Differential Revision: https://reviews.llvm.org/D37215 llvm-svn: 368723
2019-08-07[ValueTracking] When calculating known bits for integer abs, make sure we're ↵Craig Topper1-4/+6
looking at a negate and not just any instruction with the nsw flag set. The matchSelectPattern code can match patterns like (x >= 0) ? x : -x for absolute value. But it can also match ((x-y) >= 0) ? (x-y) : (y-x). If the latter form was matched we can only use the nsw flag if its set on both subtracts. This match makes sure we're looking at the former case only. Differential Revision: https://reviews.llvm.org/D65692 llvm-svn: 368195
2019-07-30[FunctionAttrs] Annotate "willreturn" for AssumeLikeInstHideto Ueno1-4/+1
Summary: In D37215, AssumeLikeInstruction are regarded as `willreturn`. In this patch, annotation is added to those which don't have `willreturn` now(`sideeffect, object_size, experimental_widenable_condition`). Reviewers: jdoerfert, nikic, sstefan1 Reviewed By: nikic Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D65455 llvm-svn: 367342
2019-07-29[ValueTracking] Remove volatile check in ↵Hideto Ueno1-15/+2
isGuaranteedToTransferExecutionToSuccessor Summary: As clarified in D53184, volatile load and store do not trap. Therefore, we should remove volatile checks for instructions in `isGuaranteedToTransferExecutionToSuccessor`. Reviewers: jdoerfert, efriedma, nikic Reviewed By: nikic Subscribers: hiraditya, jfb, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D65375 llvm-svn: 367226
2019-07-17Basic codegen for MTE stack tagging.Evgeniy Stepanov1-1/+2
Implement IR intrinsics for stack tagging. Generated code is very unoptimized for now. Two special intrinsics, llvm.aarch64.irg.sp and llvm.aarch64.tagp are used to implement a tagged stack frame pointer in a virtual register. Differential Revision: https://reviews.llvm.org/D64172 llvm-svn: 366360
2019-07-15[ValueTracking] Look through constant Int2Ptr/Ptr2Int expressionsJohannes Doerfert1-0/+9
Summary: This is analogous to the int2ptr/ptr2int instruction handling introduced in D54956. Reviewers: fhahn, efriedma, spatel, nlopes, sanjoy, lebedev.ri Subscribers: hiraditya, bollu, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D64708 llvm-svn: 366036
2019-07-12isBytewiseValue checks ConstantVector element by elementVitaly Buka1-6/+1
Summary: Vector of the same value with few undefs will sill be considered "Bytewise" Reviewers: eugenis, pcc, jfb Reviewed By: jfb Subscribers: dexonsmith, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D64031 llvm-svn: 365971
2019-07-12Return Undef from isBytewiseValue for empty arrays or structsVitaly Buka1-0/+4
Reviewers: pcc, eugenis Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D64052 llvm-svn: 365864
2019-07-12Handle IntToPtr in isBytewiseValueVitaly Buka1-0/+11
Summary: This helps with more efficient use of memset for pattern initialization From @pcc prototype for -ftrivial-auto-var-init=pattern optimizations Binary size change on CTMark, (with -fuse-ld=lld -Wl,--icf=all, similar results with default linker options) ``` master patch diff Os 8.238864e+05 8.238864e+05 0.0 O3 1.054797e+06 1.054797e+06 0.0 Os zero 8.292384e+05 8.292384e+05 0.0 O3 zero 1.062626e+06 1.062626e+06 0.0 Os pattern 8.579712e+05 8.338048e+05 -0.030299 O3 pattern 1.090502e+06 1.067574e+06 -0.020481 ``` Zero vs Pattern on master ``` zero pattern diff Os 8.292384e+05 8.579712e+05 0.036578 O3 1.062626e+06 1.090502e+06 0.025124 ``` Zero vs Pattern with the patch ``` zero pattern diff Os 8.292384e+05 8.338048e+05 0.003333 O3 1.062626e+06 1.067574e+06 0.003193 ``` Reviewers: pcc, eugenis Subscribers: hiraditya, cfe-commits, llvm-commits Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D63967 llvm-svn: 365858
2019-07-11Replace three "strip & accumulate" implementations with a single oneJohannes Doerfert1-53/+1
This patch replaces the three almost identical "strip & accumulate" implementations for constant pointer offsets with a single one, combining the respective functionalities. The old interfaces are kept for now. Differential Revision: https://reviews.llvm.org/D64468 llvm-svn: 365723
2019-07-10NFC: Pass DataLayout into isBytewiseValueVitaly Buka1-5/+6
Summary: We will need to handle IntToPtr which I will submit in a separate patch as it's not going to be NFC. Reviewers: eugenis, pcc Reviewed By: eugenis Subscribers: hiraditya, cfe-commits, llvm-commits Tags: #clang, #llvm Differential Revision: https://reviews.llvm.org/D63940 llvm-svn: 365709
2019-07-09OpaquePtr: add Type parameter to Loads analysis API.Tim Northover1-1/+2
This makes the functions in Loads.h require a type to be specified independently of the pointer Value so that when pointers have no structure other than address-space, it can still do its job. Most callers had an obvious memory operation handy to provide this type, but a SROA and ArgumentPromotion were doing more complicated analysis. They get updated to merge the properties of the various instructions they were considering. llvm-svn: 365468
2019-07-03Teach ValueTracking that aarch64.irg result aliases its input.Evgeniy Stepanov1-1/+2
Reviewers: javed.absar, olista01 Subscribers: kristof.beyls, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D64103 llvm-svn: 365079
2019-06-27Use "willreturn" in isGuaranteedToTransferExecutionToSuccessorJohannes Doerfert1-0/+5
The `willreturn` function attribute guarantees that a function call will come back to the call site if the call is also known not to throw. Therefore, this attribute can be used in `isGuaranteedToTransferExecutionToSuccessor`. Patch by Hideto Ueno (@uenoku) Reviewers: jdoerfert, sstefan1 Reviewed By: jdoerfert Subscribers: hiraditya, jfb, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D63372 llvm-svn: 364580
2019-06-13[LangRef] Clarify poison semanticsNikita Popov1-0/+2
I find the current documentation of poison somewhat confusing, mainly because its use of "undefined behavior" doesn't seem to align with our usual interpretation (of immediate UB). Especially the sentence "any instruction that has a dependence on a poison value has undefined behavior" is very confusing. Clarify poison semantics by: * Replacing the introductory paragraph with the standard rationale for having poison values. * Spelling out that instructions depending on poison return poison. * Spelling out how we go from a poison value to immediate undefined behavior and give the two examples we currently use in ValueTracking. * Spelling out that side effects depending on poison are UB. Differential Revision: https://reviews.llvm.org/D63044 llvm-svn: 363320
2019-06-13Add a clarifying comment about branching on poisonPhilip Reames1-0/+4
I recently got this wrong (again), and I'm sure I'm not the only one. Put a comment in the logical place someone would look to "fix" the obvious "missed optimization" which arrises based on the common misunderstanding. Hopefully, this will save others time. :) llvm-svn: 363318
2019-06-13[EarlyCSE] Ensure equal keys have the same hash valueJoseph Tremoulet1-2/+10
Summary: The logic in EarlyCSE that looks through 'not' operations in the predicate recognizes e.g. that `select (not (cmp sgt X, Y)), X, Y` is equivalent to `select (cmp sgt X, Y), Y, X`. Without this change, however, only the latter is recognized as a form of `smin X, Y`, so the two expressions receive different hash codes. This leads to missed optimization opportunities when the quadratic probing for the two hashes doesn't happen to collide, and assertion failures when probing doesn't collide on insertion but does collide on a subsequent table grow operation. This change inverts the order of some of the pattern matching, checking first for the optional `not` and then for the min/max/abs patterns, so that e.g. both expressions above are recognized as a form of `smin X, Y`. It also adds an assertion to isEqual verifying that it implies equal hash codes; this fires when there's a collision during insertion, not just grow, and so will make it easier to notice if these functions fall out of sync again. A new flag --earlycse-debug-hash is added which can be used when changing the hash function; it forces hash collisions so that any pair of values inserted which compare as equal but hash differently will be caught by the isEqual assertion. Reviewers: spatel, nikic Reviewed By: spatel, nikic Subscribers: lebedev.ri, arsenm, craig.topper, efriedma, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D62644 llvm-svn: 363274
2019-06-10Factor out a helper function for readability and reuse in a future patch [NFC]Philip Reames1-2/+8
llvm-svn: 362980
2019-05-28[ValueTracking][ConstantRange] Distinguish low/high always overflowNikita Popov1-2/+4
In order to fold an always overflowing signed saturating add/sub, we need to know in which direction the always overflow occurs. This patch splits up AlwaysOverflows into AlwaysOverflowsLow and AlwaysOverflowsHigh to pass through this information (but it is not used yet). Differential Revision: https://reviews.llvm.org/D62463 llvm-svn: 361858
2019-05-26[ValueTracking] Base computeOverflowForUnsignedMul() on ConstantRange code; NFCINikita Popov1-68/+34
The implementation in ValueTracking and ConstantRange are equally powerful, reuse the one in ConstantRange, which will make this easier to extend. llvm-svn: 361723
2019-05-08Revert "[ValueTracking] Improve isKnowNonZero for Ints"Nikita Popov1-13/+13
This reverts commit 3b137a495686bd6018d115ea82fb8bb7718349fd. As reported in https://reviews.llvm.org/D60846, this is causing miscompiles. llvm-svn: 360260
2019-05-08[ValueTracking] Improve isKnowNonZero for IntsDan Robertson1-13/+13
Improve isKnownNonZero for integers in order to improve cttz optimizations. Differential Revision: https://reviews.llvm.org/D60846 llvm-svn: 360222
2019-05-07[ValueTracking] add logic for known-never-nan with minnum/maxnumSanjay Patel1-0/+5
From the LangRef: "Returns NaN only if both operands are NaN." llvm-svn: 360206
2019-04-24Add "const" in GetUnderlyingObjects. NFCBjorn Pettersson1-9/+10
Summary: Both the input Value pointer and the returned Value pointers in GetUnderlyingObjects are now declared as const. It turned out that all current (in-tree) uses of GetUnderlyingObjects were trivial to update, being satisfied with have those Value pointers declared as const. Actually, in the past several of the users had to use const_cast, just because of ValueTracking not providing a version of GetUnderlyingObjects with "const" Value pointers. With this patch we get rid of those const casts. Reviewers: hfinkel, materi, jkorous Reviewed By: jkorous Subscribers: dexonsmith, jkorous, jholewinski, sdardis, eraman, hiraditya, jrtc27, atanasyan, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D61038 llvm-svn: 359072
2019-04-21[ConstantRange] Add getNonEmpty() constructorNikita Popov1-2/+1
ConstantRanges have an annoying special case: If upper and lower are the same, it can be either an empty or a full set. When constructing constant ranges nearly always a full set is intended, but this still requires an explicit check in many places. This revision adds a getNonEmpty() constructor that disambiguates this case: If upper and lower are the same, a full set is created. Differential Revision: https://reviews.llvm.org/D60947 llvm-svn: 358854
2019-04-16[IR] Add WithOverflowInst classNikita Popov1-13/+2
This adds a WithOverflowInst class with a few helper methods to get the underlying binop, signedness and nowrap type and makes use of it where sensible. There will be two more uses in D60650/D60656. The refactorings are all NFC, though I left some TODOs where things could be improved. In particular we have two places where add/sub are handled but mul isn't. Differential Revision: https://reviews.llvm.org/D60668 llvm-svn: 358512
2019-04-11[ValueTracking] Change if-else chain into switch in computeKnownBitsFromAssumeSander de Smalen1-8/+18
This is a follow-up patch to D60504 to further improve performance issues in computeKnownBitsFromAssume. The patch is NFC, but may improve compile-time performance if the compiler isn't clever enough to do the optimization itself. llvm-svn: 358163
2019-04-10Improve compile-time performance in computeKnownBitsFromAssume.Sander de Smalen1-217/+214
This patch changes the order of pattern matching by first testing a compare instruction's predicate, before doing the pattern match for the whole expression tree. Patch by Paul Walker. Reviewed By: spatel Differential Revision: https://reviews.llvm.org/D60504 llvm-svn: 358097
2019-04-09[ValueTracking] Use computeConstantRange() for signed sub overflow determinationNikita Popov1-6/+4
This is the same change as D60420 but for signed sub rather than signed add: Range information is intersected into the known bits result, allows to detect more no/always overflow conditions. Differential Revision: https://reviews.llvm.org/D60469 llvm-svn: 358020
2019-04-09[ValueTracking] Use computeConstantRange() in signed add overflow determinationNikita Popov1-8/+6
This is D59386 for the signed add case. The computeConstantRange() result is now intersected into the existing known bits information, allowing to detect additional no-overflow/always-overflow conditions (though the latter isn't used yet). This (finally...) covers the motivating case from D59071. Differential Revision: https://reviews.llvm.org/D60420 llvm-svn: 358014
2019-04-09[ValueTracking] Use ConstantRange methods; NFCNikita Popov1-3/+3
Switch part of the computeOverflowForSignedAdd() implementation to use Range.isAllNegative() rather than KnownBits.isNegative() and similar. They do the same thing, but using the ConstantRange methods allows dropping the KnownBits variables more easily in D60420. llvm-svn: 357969
2019-04-09[ValueTracking] Explicitly specify intersection type; NFCNikita Popov1-2/+5
Preparation for D60420. llvm-svn: 357968
2019-04-07Reapply [ValueTracking] Support min/max selects in computeConstantRange()Nikita Popov1-1/+22
Add support for min/max flavor selects in computeConstantRange(), which allows us to fold comparisons of a min/max against a constant in InstSimplify. This fixes an infinite InstCombine loop, with the test case taken from D59378. Relative to the previous iteration, this contains some adjustments for AMDGPU med3 tests: The AMDGPU target runs InstSimplify prior to codegen, which ends up constant folding some existing med3 tests after this change. To preserve these tests a hidden -amdgpu-scalar-ir-passes option is added, which allows disabling scalar IR passes (that use InstSimplify) for testing purposes. Differential Revision: https://reviews.llvm.org/D59506 llvm-svn: 357870
2019-03-24[ConstantRange] Add getFull() + getEmpty() named constructors; NFCNikita Popov1-1/+1
This adds ConstantRange::getFull(BitWidth) and ConstantRange::getEmpty(BitWidth) named constructors as more readable alternatives to the current ConstantRange(BitWidth, /* full */ false) and similar. Additionally private getFull() and getEmpty() member functions are added which return a full/empty range with the same bit width -- these are commonly needed inside ConstantRange.cpp. The IsFullSet argument in the ConstantRange(BitWidth, IsFullSet) constructor is now mandatory for the few usages that still make use of it. Differential Revision: https://reviews.llvm.org/D59716 llvm-svn: 356852
2019-03-22[ValueTracking] Avoid redundant known bits calculation in ↵Nikita Popov1-6/+8
computeOverflowForSignedAdd() We're already computing the known bits of the operands here. If the known bits of the operands can determine the sign bit of the result, we'll already catch this in signedAddMayOverflow(). The only other way (and as the comment already indicates) we'll get new information from computing known bits on the whole add, is if there's an assumption on it. As such, we change the code to only compute known bits from assumptions, instead of computing full known bits on the add (which would unnecessarily recompute the known bits of the operands as well). Differential Revision: https://reviews.llvm.org/D59473 llvm-svn: 356785
2019-03-21[ValueTracking] Use ConstantRange based overflow check for signed subNikita Popov1-10/+5
This is D59450, but for signed sub. This case is not NFC, because the overflow logic in ConstantRange is more powerful than the existing check. This resolves the TODO in the function. I've added two tests to show that this indeed catches more cases than the previous logic, but the main correctness test coverage here is in the existing ConstantRange unit tests. Differential Revision: https://reviews.llvm.org/D59617 llvm-svn: 356685
2019-03-20[ValueTracking] Compute range for abs without nswNikita Popov1-7/+8
This is a small followup to D59511. The code that was moved into computeConstantRange() there is a bit overly conversative: If the abs is not nsw, it does not compute any range. However, abs without nsw still has a well-defined contiguous unsigned range from 0 to SIGNED_MIN. This is a lot less useful than the usual 0 to SIGNED_MAX range, but if we're already here we might as well specify it... Differential Revision: https://reviews.llvm.org/D59563 llvm-svn: 356586
2019-03-19[ValueTracking] Use computeConstantRange() for unsigned add/sub overflowNikita Popov1-14/+25
Improve computeOverflowForUnsignedAdd/Sub in ValueTracking by intersecting the computeConstantRange() result into the ConstantRange created from computeKnownBits(). This allows us to detect some additional never/always overflows conditions that can't be determined from known bits. This revision also adds basic handling for constants to computeConstantRange(). Non-splat vectors will be handled in a followup. The signed case will also be handled in a followup, as it needs some more groundwork. Differential Revision: https://reviews.llvm.org/D59386 llvm-svn: 356489
2019-03-19[SelectionDAG] Handle unary SelectPatternFlavor for ABS case in ↵Simon Pilgrim1-0/+4
SelectionDAGBuilder::visitSelect These changes are related to PR37743 and include: SelectionDAGBuilder::visitSelect handles the unary SelectPatternFlavor::SPF_ABS case to build ABS node. Delete the redundant recognizer of the integer ABS pattern from the DAGCombiner. Add promoting the integer ABS node in the LegalizeIntegerType. Expand-based legalization of integer result for the ABS nodes. Expand-based legalization of ABS vector operations. Add some integer abs testcases for different typesizes for Thumb arch Add the custom ABS expanding and change the SAD pattern recognizer for X86 arch: The i64 result of the ABS is expanded to: tmp = (SRA, Hi, 31) Lo = (UADDO tmp, Lo) Hi = (XOR tmp, (ADDCARRY tmp, hi, Lo:1)) Lo = (XOR tmp, Lo) The "detectZextAbsDiff" function is changed for the recognition of pattern with the ABS node. Given a ABS node, detect the following pattern: (ABS (SUB (ZERO_EXTEND a), (ZERO_EXTEND b))). Change integer abs testcases for codegen with the ABS node support for AArch64. Indicate that the ABS is legal for the i64 type when the NEON is supported. Change the integer abs testcases to show changing of codegen. Add combine and legalization of ABS nodes for Thumb arch. Extend 'matchSelectPattern' to recognize the ABS patterns with ICMP_SGE condition. For discussion, see https://bugs.llvm.org/show_bug.cgi?id=37743 Patch by: @ikulagin (Ivan Kulagin) Differential Revision: https://reviews.llvm.org/D49837 llvm-svn: 356468
2019-03-18Revert "[ValueTracking][InstSimplify] Support min/max selects in ↵Nikita Popov1-22/+1
computeConstantRange()" This reverts commit 106f0cdefb02afc3064268dc7a71419b409ed2f3. This change impacts the AMDGPU smed3.ll and umed3.ll codegen tests. llvm-svn: 356424
2019-03-18[ValueTracking][InstSimplify] Support min/max selects in computeConstantRange()Nikita Popov1-1/+22
Add support for min/max flavor selects in computeConstantRange(), which allows us to fold comparisons of a min/max against a constant in InstSimplify. This was suggested by spatel as an alternative approach to D59378. I've also added the infinite looping test from that revision here. Differential Revision: https://reviews.llvm.org/D59506 llvm-svn: 356415
2019-03-18[ValueTracking][InstSimplify] Move abs handling into computeConstantRange(); NFCNikita Popov1-0/+32
This is preparation for D59506. The InstructionSimplify abs handling is moved into computeConstantRange(), which is the general place for such calculations. This is NFC and doesn't affect the existing tests in test/Transforms/InstSimplify/icmp-abs-nabs.ll. Differential Revision: https://reviews.llvm.org/D59511 llvm-svn: 356409
2019-03-17[ValueTracking] Use ConstantRange overflow check for signed add; NFCNikita Popov1-48/+8
This is the same change as rL356290, but for signed add. It replaces the existing ripple logic with the overflow logic in ConstantRange. This is NFC in that it should return NeverOverflow in exactly the same cases as the previous implementation. However, it does make computeOverflowForSignedAdd() more powerful by now also determining AlwaysOverflows conditions. As none of its consumers handle this yet, this has no impact on optimization. Making use of AlwaysOverflows in with.overflow folding will be handled as a followup. Differential Revision: https://reviews.llvm.org/D59450 llvm-svn: 356345
2019-03-17[ConstantRange] Add fromKnownBits() methodNikita Popov1-11/+8
Following the suggestion in D59450, I'm moving the code for constructing a ConstantRange from KnownBits out of ValueTracking, which also allows us to test this code independently. I'm adding this method to ConstantRange rather than KnownBits (which would have been a bit nicer API wise) to avoid creating a dependency from Support to IR, where ConstantRange lives. Differential Revision: https://reviews.llvm.org/D59475 llvm-svn: 356339
2019-03-15[ValueTracking] Use ConstantRange overflow checks for unsigned add/sub; NFCNikita Popov1-20/+26
Use the methods introduced in rL356276 to implement the computeOverflowForUnsigned(Add|Sub) functions in ValueTracking, by converting the KnownBits into a ConstantRange. This is NFC: The existing KnownBits based implementation uses the same logic as the the ConstantRange based one. This is not the case for the signed equivalents, so I'm only changing unsigned here. This is in preparation for D59386, which will also intersect the computeConstantRange() result into the range determined from KnownBits. llvm-svn: 356290
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