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Auto merge of #119911 - NCGThompson:is-statically-known, r=oli-obk

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Replacement of #114390: Add new intrinsic `is_var_statically_known` and optimize pow for powers of two

This adds a new intrinsic `is_val_statically_known` that lowers to [``@llvm.is.constant.*`](https://llvm.org/docs/LangRef.html#llvm-is-constant-intrinsic).` It also applies the intrinsic in the int_pow methods to recognize and optimize the idiom `2isize.pow(x)`. See #114390 for more discussion.

While I have extended the scope of the power of two optimization from #114390, I haven't added any new uses for the intrinsic. That can be done in later pull requests.

Note: When testing or using the library, be sure to use `--stage 1` or higher. Otherwise, the intrinsic will be a noop and the doctests will be skipped. If you are trying out edits, you may be interested in [`--keep-stage 0`](https://rustc-dev-guide.rust-lang.org/building/suggested.html#faster-builds-with---keep-stage).

Fixes #47234
Resolves #114390
`@Centri3`
This commit is contained in:
bors 2024-01-25 05:16:53 +00:00
commit 039d887928
17 changed files with 634 additions and 154 deletions
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14
compiler/rustc_codegen_llvm/src/context.rs
View file

@ -916,6 +916,20 @@ impl<'ll> CodegenCx<'ll, '_> {
ifn!("llvm.lifetime.start.p0i8", fn(t_i64, ptr) -> void);
ifn!("llvm.lifetime.end.p0i8", fn(t_i64, ptr) -> void);
// FIXME: This is an infinitesimally small portion of the types you can
// pass to this intrinsic, if we can ever lazily register intrinsics we
// should register these when they're used, that way any type can be
// passed.
ifn!("llvm.is.constant.i1", fn(i1) -> i1);
ifn!("llvm.is.constant.i8", fn(t_i8) -> i1);
ifn!("llvm.is.constant.i16", fn(t_i16) -> i1);
ifn!("llvm.is.constant.i32", fn(t_i32) -> i1);
ifn!("llvm.is.constant.i64", fn(t_i64) -> i1);
ifn!("llvm.is.constant.i128", fn(t_i128) -> i1);
ifn!("llvm.is.constant.isize", fn(t_isize) -> i1);
ifn!("llvm.is.constant.f32", fn(t_f32) -> i1);
ifn!("llvm.is.constant.f64", fn(t_f64) -> i1);
ifn!("llvm.expect.i1", fn(i1, i1) -> i1);
ifn!("llvm.eh.typeid.for", fn(ptr) -> t_i32);
ifn!("llvm.localescape", fn(...) -> void);

4
compiler/rustc_codegen_llvm/src/intrinsic.rs
View file

@ -119,6 +119,10 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
sym::likely => {
self.call_intrinsic("llvm.expect.i1", &[args[0].immediate(), self.const_bool(true)])
}
sym::is_val_statically_known => self.call_intrinsic(
&format!("llvm.is.constant.{:?}", args[0].layout.immediate_llvm_type(self.cx)),
&[args[0].immediate()],
),
sym::unlikely => self
.call_intrinsic("llvm.expect.i1", &[args[0].immediate(), self.const_bool(false)]),
kw::Try => {