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Tell LLVM that the negation in <*const T>::sub cannot overflow

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Today it's just `sub` <https://rust.godbolt.org/z/8EzEPnMr5>; with this PR it's `sub nsw`.
This commit is contained in:
Scott McMurray 2023-08-10 23:00:39 -07:00
parent 8e7fd55131
commit ab6e2bc3d0
3 changed files with 58 additions and 5 deletions
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34
tests/codegen/ptr-arithmetic.rs Normal file
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// compile-flags: -O -Z merge-functions=disabled
// ignore-debug (the extra assertions get in the way)
#![crate_type = "lib"]
// CHECK-LABEL: ptr @i32_add(
// CHECK-SAME: [[WORD:i[0-9]+]] noundef %n)
#[no_mangle]
pub unsafe fn i32_add(p: *const i32, n: usize) -> *const i32 {
// CHECK: %[[TEMP:.+]] = getelementptr inbounds i32, ptr %p, [[WORD]] %n
// CHECK: ret ptr %[[TEMP]]
p.add(n)
}
// Ensure we tell LLVM that the negation in `sub` can't overflow.
// CHECK-LABEL: ptr @i32_sub(
// CHECK-SAME: [[WORD:i[0-9]+]] noundef %n)
#[no_mangle]
pub unsafe fn i32_sub(p: *const i32, n: usize) -> *const i32 {
// CHECK: %[[DELTA:.+]] = sub nsw [[WORD]] 0, %n
// CHECK: %[[TEMP:.+]] = getelementptr inbounds i32, ptr %p, [[WORD]] %[[DELTA]]
// CHECK: ret ptr %[[TEMP]]
p.sub(n)
}
// CHECK-LABEL: ptr @i32_offset(
// CHECK-SAME: [[WORD:i[0-9]+]] noundef %d)
#[no_mangle]
pub unsafe fn i32_offset(p: *const i32, d: isize) -> *const i32 {
// CHECK: %[[TEMP:.+]] = getelementptr inbounds i32, ptr %p, [[WORD]] %d
// CHECK: ret ptr %[[TEMP]]
p.offset(d)
}