Commit 2b5e239

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Auto merge of #144225 - purplesyringa:unwinding-intrinsics, r=nikic

Don't special-case llvm.* as nounwind Certain LLVM intrinsics, such as `llvm.wasm.throw`, can unwind. Marking them as nounwind causes us to skip cleanup of locals and optimize out `catch_unwind` under inlining or when `llvm.wasm.throw` is used directly by user code. The motivation for forcibly marking llvm.* as nounwind is no longer present: most intrinsics are linked as `extern "C"` or other non-unwinding ABIs, so we won't codegen `invoke` for them anyway. Closes #132416. `@rustbot` label +T-compiler +A-panic

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+25

-10

lines changed

compiler/rustc_codegen_ssa/src
- codegen_attrs.rs
library/stdarch/crates/core_arch/src/wasm32
- mod.rs
tests/codegen-llvm
- wasm_exceptions.rs

3 files changed

+25

-10

lines changed

`‎compiler/rustc_codegen_ssa/src/codegen_attrs.rs`

Lines changed: 0 additions & 9 deletions

Original file line number	Diff line number	Diff line change
`@@ -511,15 +511,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {`
`511`	`511`	`err.emit();`
`512`	`512`	`}`
`513`	`513`
`514`		`- // Any linkage to LLVM intrinsics for now forcibly marks them all as never`
`515`		- // unwinds since LLVM sometimes can't handle codegen which `invoke`s
`516`		`- // intrinsic functions.`
`517`		`- if let Some(name) = &codegen_fn_attrs.link_name`
`518`		`- && name.as_str().starts_with("llvm.")`
`519`		`- {`
`520`		`- codegen_fn_attrs.flags \|= CodegenFnAttrFlags::NEVER_UNWIND;`
`521`		`- }`
`522`		`-`
`523`	`514`	`if let Some(features) = check_tied_features(`
`524`	`515`	`tcx.sess,`
`525`	`516`	`&codegen_fn_attrs`

`‎library/stdarch/crates/core_arch/src/wasm32/mod.rs`

Lines changed: 10 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -191,6 +191,16 @@ unsafe extern "C-unwind" {`
`191`	`191`	`// #[cfg_attr(test, assert_instr(throw, TAG = 0, ptr = core::ptr::null_mut()))]`
`192`	`192`	`#[inline]`
`193`	`193`	`#[unstable(feature = "wasm_exception_handling_intrinsics", issue = "122465")]`
	`194`	+// FIXME: Since this instruction unwinds, `core` built with `-C panic=unwind`
	`195`	+// cannot be linked with `-C panic=abort` programs. But that's not
	`196`	`+// entirely supported anyway, because runtimes without EH support won't`
	`197`	+// be able to handle `try` blocks in `-C panic=unwind` crates either.
	`198`	+// We ship `-C panic=abort` `core`, so this doesn't affect users
	`199`	+// directly. Resolving this will likely require patching out both `try`
	`200`	+// and `throw` instructions, at which point we can look into whitelisting
	`201`	`+// this function in the compiler to allow linking.`
	`202`	`+// See https://github.com/rust-lang/rust/issues/118168.`
	`203`	`+#[allow(ffi_unwind_calls)]`
`194`	`204`	`pub unsafe fn throw<const TAG: i32>(ptr: *mut u8) -> ! {`
`195`	`205`	`static_assert!(TAG == 0); // LLVM only supports tag 0 == C++ right now.`
`196`	`206`	`wasm_throw(TAG, ptr)`

`‎tests/codegen-llvm/wasm_exceptions.rs`

Lines changed: 15 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -2,7 +2,7 @@`
`2`	`2`	`//@ compile-flags: -C panic=unwind -Z emscripten-wasm-eh`
`3`	`3`
`4`	`4`	`#![crate_type = "lib"]`
`5`		`-#![feature(core_intrinsics)]`
	`5`	`+#![feature(core_intrinsics, wasm_exception_handling_intrinsics)]`
`6`	`6`
`7`	`7`	`extern "C-unwind" {`
`8`	`8`	`fn may_panic();`
`@@ -57,3 +57,17 @@ pub fn test_rtry() {`
`57`	`57`	`// CHECK: {{.}} = catchpad within {{.}} [ptr null]`
`58`	`58`	`// CHECK: catchret`
`59`	`59`	`}`
	`60`	`+`
	`61`	`+// Make sure the intrinsic is not inferred as nounwind. This is a regression test for #132416.`
	`62`	`+// CHECK-LABEL: @test_intrinsic() {{.*}} @__gxx_wasm_personality_v0`
	`63`	`+#[no_mangle]`
	`64`	`+pub fn test_intrinsic() {`
	`65`	`+ let _log_on_drop = LogOnDrop;`
	`66`	`+ unsafe {`
	`67`	`+ core::arch::wasm32::throw::<0>(core::ptr::null_mut());`
	`68`	`+ }`
	`69`	`+`
	`70`	`+ // CHECK-NOT: call`
	`71`	`+ // CHECK: invoke void @llvm.wasm.throw(i32 noundef 0, ptr noundef null)`
	`72`	`+ // CHECK: %cleanuppad = cleanuppad within none []`
	`73`	`+}`

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Commit 2b5e239

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3 files changed

3 files changed

`‎compiler/rustc_codegen_ssa/src/codegen_attrs.rs`

`‎library/stdarch/crates/core_arch/src/wasm32/mod.rs`

`‎tests/codegen-llvm/wasm_exceptions.rs`

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