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for negative divisors, INT_MIN divisors
As discussed in the review, that fold is only valid for positive
divisors, so while we can negate negative divisors,
we have to special-case INT_MIN.
llvm-svn: 367294
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Summary:
Four things here:
1. Generalize the fold to handle non-splat divisors. Reasonably trivial.
2. Unban power-of-two divisors. I don't see any reason why they should
be illegal.
* There is no ban in Hacker's Delight
* I think the ban came from the same bug that caused the miscompile
in the base patch - in `floor((2^W - 1) / D)` we were dividing by
`D0` instead of `D`, and we **were** ensuring that `D0` is not `1`,
which made sense.
3. Unban `1` divisors. I no longer believe Hacker's Delight actually says
that the fold is invalid for `D = 0`. Further considerations:
* We know that
* `(X u% 1) == 0` can be constant-folded to `1`,
* `(X u% 1) != 0` can be constant-folded to `0`,
* Also, we know that
* `X u<= -1` can be constant-folded to `1`,
* `X u> -1` can be constant-folded to `0`,
* https://godbolt.org/z/7jnZJX https://rise4fun.com/Alive/oF6p
* We know will end up with the following:
`(setule/setugt (rotr (mul N, P), K), Q)`
* Therefore, for given new DAG nodes and comparison predicates
(`ule`/`ugt`), we will still produce the correct answer if:
`Q` is a all-ones constant; and both `P` and `K` are *anything*
other than `undef`.
* The fold will indeed produce `Q = all-ones`.
4. Try to re-splat the `P` and `K` vectors - we don't care about
their values for the lanes where divisor was `1`.
Reviewers: RKSimon, hermord, craig.topper, spatel, xbolva00
Reviewed By: RKSimon
Subscribers: hiraditya, javed.absar, dexonsmith, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63963
llvm-svn: 366637
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tests with '1' divisor)
llvm-svn: 364661
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llvm-svn: 364642
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Summary:
I'm submitting a new revision since i don't understand how to reclaim/reopen/take over the existing one, D50222.
There is no such action in "Add Action" menu...
This implements an optimization described in Hacker's Delight 10-17: when `C` is constant,
the result of `X % C == 0` can be computed more cheaply without actually calculating the remainder.
The motivation is discussed here: https://bugs.llvm.org/show_bug.cgi?id=35479.
This is a recommit, the original commit rL364563 was reverted in rL364568
because test-suite detected miscompile - the new comparison constant 'Q'
was being computed incorrectly (we divided by `D0` instead of `D`).
Original patch D50222 by @hermord (Dmytro Shynkevych)
Notes:
- In principle, it's possible to also handle the `X % C1 == C2` case, as discussed on bugzilla.
This seems to require an extra branch on overflow, so I refrained from implementing this for now.
- An explicit check for when the `REM` can be reduced to just its LHS is included:
the `X % C` == 0 optimization breaks `test1` in `test/CodeGen/X86/jump_sign.ll` otherwise.
I hadn't managed to find a better way to not generate worse output in this case.
- The `test/CodeGen/X86/jump_sign.ll` regresses, and is being fixed by a followup patch D63390.
Reviewers: RKSimon, craig.topper, spatel, hermord, xbolva00
Reviewed By: RKSimon, xbolva00
Subscribers: dexonsmith, kristina, xbolva00, javed.absar, llvm-commits, hermord
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D63391
llvm-svn: 364600
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The fold (D63391) uses multiplicativeInverse(),
but it is not guaranteed to always succeed,
and '100' appears to be one of the problematic values.
llvm-svn: 364578
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First half of PR40800, this patch adds DAG undef handling to icmp instructions to match the behaviour in llvm::ConstantFoldCompareInstruction and SimplifyICmpInst, this permits constant folding of vector comparisons where some elements had been reduced to UNDEF (by SimplifyDemandedVectorElts etc.).
This involved a lot of tweaking to reduced tests as bugpoint loves to reduce icmp arguments to undef........
Differential Revision: https://reviews.llvm.org/D59363
llvm-svn: 356938
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As discussed on D50222
llvm-svn: 343934
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For https://reviews.llvm.org/D50222
Patch by: hermord (Dmytro Shynkevych)!
llvm-svn: 341953
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