Missed fold: `x == c || (c + 1 <= x && x <= c2)` => `(c <= x && x <= c2)`

[Kmeakin]

C++ example

#include <stdint.h>

using u32 = uint32_t;

auto inline in_range(auto x, auto lo, auto hi) -> bool {
    return lo <= x && x <= hi;
}

extern "C" {
auto src(u32 c) -> bool { return (c == 0x7f) || in_range(c, 0x80, 0x9f); }
auto tgt(u32 c) -> bool { return in_range(c, 0x7f, 0x9f); }
}

gives

src:
        mov     w8, #128
        cmp     w0, #127
        and     w9, w0, #0xffffffe0
        ccmp    w9, w8, #4, ne
        cset    w0, eq
        ret

tgt:
        sub     w8, w0, #127
        cmp     w8, #33
        cset    w0, lo
        ret

Alive proof

define dso_local noundef i1 @src(i32 noundef %0) local_unnamed_addr #0 {
  %2 = icmp eq i32 %0, 127
  %3 = and i32 %0, -32
  %4 = icmp eq i32 %3, 128
  %5 = or i1 %2, %4
  ret i1 %5
}

define dso_local noundef i1 @tgt(i32 noundef %0) local_unnamed_addr #0 {
  %2 = add i32 %0, -127
  %3 = icmp ult i32 %2, 33
  ret i1 %3
}

Motivation

Codegen for char::is_control in Rust's stdlib

[dtcxzyw]

%3 = and i32 %0, -32
%4 = icmp eq i32 %3, 128

We can handle this pattern in foldAndOrOfICmpsUsingRanges.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor is working on this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
2. Leave a comment indicating that you are working on the issue, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Karl Meakin (Kmeakin)

# C++ example

#include <stdint.h>

using u32 = uint32_t;

auto inline in_range(auto x, auto lo, auto hi) -> bool {
    return lo <= x && x <= hi;
}

extern "C" {
auto src(u32 c) -> bool { return (c == 0x7f) || in_range(c, 0x80, 0x9f); }
auto tgt(u32 c) -> bool { return in_range(c, 0x7f, 0x9f); }
}

gives

src:
        mov     w8, #<!-- -->128
        cmp     w0, #<!-- -->127
        and     w9, w0, #<!-- -->0xffffffe0
        ccmp    w9, w8, #<!-- -->4, ne
        cset    w0, eq
        ret

tgt:
        sub     w8, w0, #<!-- -->127
        cmp     w8, #<!-- -->33
        cset    w0, lo
        ret

Alive proof

define dso_local noundef i1 @<!-- -->src(i32 noundef %0) local_unnamed_addr #<!-- -->0 {
  %2 = icmp eq i32 %0, 127
  %3 = and i32 %0, -32
  %4 = icmp eq i32 %3, 128
  %5 = or i1 %2, %4
  ret i1 %5
}

define dso_local noundef i1 @<!-- -->tgt(i32 noundef %0) local_unnamed_addr #<!-- -->0 {
  %2 = add i32 %0, -127
  %3 = icmp ult i32 %2, 33
  ret i1 %3
}

Motivation

Codegen for char::is_control in Rust's stdlib

[flovent]

I would like to work on this, can i get assigned? thank you!

[dtcxzyw]

@flovent Please read https://llvm.org/docs/InstCombineContributorGuide.html before submitting a patch. Good luck :)

[flovent]

I think i may not have enough time for resolving this recently, other people who are interested can take this.

Can you unassign me? @dtcxzyw sorry about that.

[pedroclobo]

I would like to work on this. May I be assigned to it?