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Re-enable extension of bool return values on x86_64 #163917

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Merged
rust-bors merged 2 commits into from
Oct 10, 2026
+49 −22
Merged

Re-enable extension of bool return values on x86_64 #163917

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294ff0f
Add test coverage
saethlin Oct 7, 2026
a0f1885
Fix the bug by enabling extension for bool returns on x86_64
saethlin Oct 7, 2026
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4 changes: 3 additions & 1 deletion compiler/rustc_target/src/callconv/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -565,7 +565,9 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
// Only integers have signedness
if let BackendRepr::Scalar(scalar) = self.layout.backend_repr
&& let Primitive::Int(i, signed) = scalar.primitive()
&& i.size().bits() < bits
// bools are i1 but their primitive is i8. Unlike other types,
// bools can be extended to their primitive size.
&& (i.size().bits() < bits || self.layout.backend_repr.is_bool())
&& let PassMode::Direct(ref mut attrs) = self.mode
{
if signed {
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5 changes: 5 additions & 0 deletions compiler/rustc_target/src/callconv/x86_64.rs
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Expand Up @@ -247,6 +247,11 @@ where
} else if is_arg || cx.target_spec().is_like_darwin {
arg.extend_integer_width_to(32);
}
// The x86_64 psABI requires bools to be zero-extended to 8-bits, with high bits unspecified.
// zeroext i1 has this behavior in the LLVM X86 backend.
if !is_arg && arg.layout.backend_repr.is_bool() {
arg.extend_integer_width_to(8);
}
}
}
};
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62 changes: 41 additions & 21 deletions tests/codegen-llvm/some-abis-do-extend-params-to-32-bits.rs
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@@ -1,10 +1,12 @@
//@ add-minicore
//@ compile-flags: -Cno-prepopulate-passes -Copt-level=0

//@ revisions:x86_64 i686 aarch64-apple aarch64-windows aarch64-linux arm riscv
//@ revisions:x86_64-linux x86_64-uefi i686 aarch64-apple aarch64-windows aarch64-linux arm riscv

//@[x86_64] compile-flags: --target x86_64-unknown-uefi
//@[x86_64] needs-llvm-components: x86
//@[x86_64-uefi] compile-flags: --target x86_64-unknown-uefi
//@[x86_64-uefi] needs-llvm-components: x86
//@[x86_64-linux] compile-flags: --target x86_64-unknown-linux-gnu
//@[x86_64-linux] needs-llvm-components: x86
//@[i686] compile-flags: --target i686-unknown-linux-musl
//@[i686] needs-llvm-components: x86
//@[aarch64-windows] compile-flags: --target aarch64-pc-windows-msvc
Expand Down Expand Up @@ -33,7 +35,8 @@ use minicore::*;
//
// ZERO/SIGN-EXTENDING TO 32 BITS NON-EXTENDING
// ============================== =======================
// x86_64: void @c_arg_bool(i1 zeroext %_a)
Comment on lines 34 to -36

@jieyouxu jieyouxu Oct 9, 2026 •
edited
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I also noticed that because of how the test is written, if codegen starts adding a zeroext on a return type where it is wrong to do so, the test will pass anyway.

Yeah, that seems a bit awkward since it defeats the purpose of the return checks...

For the non-extending return check cases, can we instead match via patterns such as

// x86_64-linux:                                    define {{(dso_local )?}}i1 @c_ret_bool()

That way if the return type gets a zeroext this check should fail. Using this pattern against the uefi one (where it does zeroext) indeed fails to match.

(This is not blocking; I think we can also do this as a follow-up, since this is pre-existing.)

@jieyouxu jieyouxu Oct 9, 2026

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Follow-up: #164016

@nikic nikic Oct 9, 2026

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Assuming we have the option to pass FileCheck arguments, you could also use something like --implicit-check-not=zeroext --implicit-check-not=signext.

@jieyouxu jieyouxu Oct 9, 2026

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Hm yeah. I'm not sure using the implicit flags is much better though, that also seems not very straightforward when looking at the actual diff right?

// x86_64-linux: void @c_arg_bool(i1 zeroext %_a)
// x86_64-uefi: void @c_arg_bool(i1 zeroext %_a)
// i686: void @c_arg_bool(i1 zeroext %_a)
// aarch64-apple: void @c_arg_bool(i1 zeroext %_a)
// aarch64-windows: void @c_arg_bool(i1 %_a)
Expand All @@ -43,7 +46,8 @@ use minicore::*;
#[no_mangle]
pub extern "C" fn c_arg_bool(_a: bool) {}

// x86_64: void @c_arg_u8(i8 zeroext %_a)
// x86_64-linux: void @c_arg_u8(i8 zeroext %_a)
// x86_64-uefi: void @c_arg_u8(i8 zeroext %_a)
// i686: void @c_arg_u8(i8 zeroext %_a)
// aarch64-apple: void @c_arg_u8(i8 zeroext %_a)
// aarch64-windows: void @c_arg_u8(i8 %_a)
Expand All @@ -53,7 +57,8 @@ pub extern "C" fn c_arg_bool(_a: bool) {}
#[no_mangle]
pub extern "C" fn c_arg_u8(_a: u8) {}

// x86_64: void @c_arg_u16(i16 zeroext %_a)
// x86_64-linux: void @c_arg_u16(i16 zeroext %_a)
// x86_64-uefi: void @c_arg_u16(i16 zeroext %_a)
// i686: void @c_arg_u16(i16 zeroext %_a)
// aarch64-apple: void @c_arg_u16(i16 zeroext %_a)
// aarch64-windows: void @c_arg_u16(i16 %_a)
Expand All @@ -63,7 +68,8 @@ pub extern "C" fn c_arg_u8(_a: u8) {}
#[no_mangle]
pub extern "C" fn c_arg_u16(_a: u16) {}

// x86_64: void @c_arg_u32(i32 %_a)
// x86_64-linux: void @c_arg_u32(i32 %_a)
// x86_64-uefi: void @c_arg_u32(i32 %_a)
// i686: void @c_arg_u32(i32 %_a)
// aarch64-apple: void @c_arg_u32(i32 %_a)
// aarch64-windows: void @c_arg_u32(i32 %_a)
Expand All @@ -73,7 +79,8 @@ pub extern "C" fn c_arg_u16(_a: u16) {}
#[no_mangle]
pub extern "C" fn c_arg_u32(_a: u32) {}

// x86_64: void @c_arg_u64(i64 %_a)
// x86_64-linux: void @c_arg_u64(i64 %_a)
// x86_64-uefi: void @c_arg_u64(i64 %_a)
// i686: void @c_arg_u64(i64 %_a)
// aarch64-apple: void @c_arg_u64(i64 %_a)
// aarch64-windows: void @c_arg_u64(i64 %_a)
Expand All @@ -83,7 +90,8 @@ pub extern "C" fn c_arg_u32(_a: u32) {}
#[no_mangle]
pub extern "C" fn c_arg_u64(_a: u64) {}

// x86_64: void @c_arg_i8(i8 signext %_a)
// x86_64-linux: void @c_arg_i8(i8 signext %_a)
// x86_64-uefi: void @c_arg_i8(i8 signext %_a)
// i686: void @c_arg_i8(i8 signext %_a)
// aarch64-apple: void @c_arg_i8(i8 signext %_a)
// aarch64-windows: void @c_arg_i8(i8 %_a)
Expand All @@ -93,7 +101,8 @@ pub extern "C" fn c_arg_u64(_a: u64) {}
#[no_mangle]
pub extern "C" fn c_arg_i8(_a: i8) {}

// x86_64: void @c_arg_i16(i16 signext %_a)
// x86_64-linux: void @c_arg_i16(i16 signext %_a)
// x86_64-uefi: void @c_arg_i16(i16 signext %_a)
// i686: void @c_arg_i16(i16 signext %_a)
// aarch64-apple: void @c_arg_i16(i16 signext %_a)
// aarch64-windows: void @c_arg_i16(i16 %_a)
Expand All @@ -103,7 +112,8 @@ pub extern "C" fn c_arg_i8(_a: i8) {}
#[no_mangle]
pub extern "C" fn c_arg_i16(_a: i16) {}

// x86_64: void @c_arg_i32(i32 %_a)
// x86_64-linux: void @c_arg_i32(i32 %_a)
// x86_64-uefi: void @c_arg_i32(i32 %_a)
// i686: void @c_arg_i32(i32 %_a)
// aarch64-apple: void @c_arg_i32(i32 %_a)
// aarch64-windows: void @c_arg_i32(i32 %_a)
Expand All @@ -113,7 +123,8 @@ pub extern "C" fn c_arg_i16(_a: i16) {}
#[no_mangle]
pub extern "C" fn c_arg_i32(_a: i32) {}

// x86_64: void @c_arg_i64(i64 %_a)
// x86_64-linux: void @c_arg_i64(i64 %_a)
// x86_64-uefi: void @c_arg_i64(i64 %_a)
// i686: void @c_arg_i64(i64 %_a)
// aarch64-apple: void @c_arg_i64(i64 %_a)
// aarch64-windows: void @c_arg_i64(i64 %_a)
Expand All @@ -123,7 +134,8 @@ pub extern "C" fn c_arg_i32(_a: i32) {}
#[no_mangle]
pub extern "C" fn c_arg_i64(_a: i64) {}

// x86_64: zeroext i1 @c_ret_bool()
// x86_64-linux: zeroext i1 @c_ret_bool()
// x86_64-uefi: zeroext i1 @c_ret_bool()
// i686: zeroext i1 @c_ret_bool()
// aarch64-apple: zeroext i1 @c_ret_bool()
// aarch64-windows: i1 @c_ret_bool()
Expand All @@ -135,7 +147,8 @@ pub extern "C" fn c_ret_bool() -> bool {
false
}

// x86_64: zeroext i8 @c_ret_u8()
// x86_64-linux: i8 @c_ret_u8()
// x86_64-uefi: zeroext i8 @c_ret_u8()
// i686: zeroext i8 @c_ret_u8()
// aarch64-apple: zeroext i8 @c_ret_u8()
// aarch64-windows: i8 @c_ret_u8()
Expand All @@ -147,7 +160,8 @@ pub extern "C" fn c_ret_u8() -> u8 {
0
}

// x86_64: zeroext i16 @c_ret_u16()
// x86_64-linux: i16 @c_ret_u16()
// x86_64-uefi: zeroext i16 @c_ret_u16()
// i686: zeroext i16 @c_ret_u16()
// aarch64-apple: zeroext i16 @c_ret_u16()
// aarch64-windows: i16 @c_ret_u16()
Expand All @@ -159,7 +173,8 @@ pub extern "C" fn c_ret_u16() -> u16 {
0
}

// x86_64: i32 @c_ret_u32()
// x86_64-linux: i32 @c_ret_u32()
// x86_64-uefi: i32 @c_ret_u32()
// i686: i32 @c_ret_u32()
// aarch64-apple: i32 @c_ret_u32()
// aarch64-windows: i32 @c_ret_u32()
Expand All @@ -171,7 +186,8 @@ pub extern "C" fn c_ret_u32() -> u32 {
0
}

// x86_64: i64 @c_ret_u64()
// x86_64-linux: i64 @c_ret_u64()
// x86_64-uefi: i64 @c_ret_u64()
// i686: i64 @c_ret_u64()
// aarch64-apple: i64 @c_ret_u64()
// aarch64-windows: i64 @c_ret_u64()
Expand All @@ -183,7 +199,8 @@ pub extern "C" fn c_ret_u64() -> u64 {
0
}

// x86_64: signext i8 @c_ret_i8()
// x86_64-linux: i8 @c_ret_i8()
// x86_64-uefi: signext i8 @c_ret_i8()
// i686: signext i8 @c_ret_i8()
// aarch64-apple: signext i8 @c_ret_i8()
// aarch64-windows: i8 @c_ret_i8()
Expand All @@ -195,7 +212,8 @@ pub extern "C" fn c_ret_i8() -> i8 {
0
}

// x86_64: signext i16 @c_ret_i16()
// x86_64-linux: i16 @c_ret_i16()
// x86_64-uefi: signext i16 @c_ret_i16()
// i686: signext i16 @c_ret_i16()
// aarch64-apple: signext i16 @c_ret_i16()
// aarch64-windows: i16 @c_ret_i16()
Expand All @@ -207,7 +225,8 @@ pub extern "C" fn c_ret_i16() -> i16 {
0
}

// x86_64: i32 @c_ret_i32()
// x86_64-linux: i32 @c_ret_i32()
// x86_64-uefi: i32 @c_ret_i32()
// i686: i32 @c_ret_i32()
// aarch64-apple: i32 @c_ret_i32()
// aarch64-windows: i32 @c_ret_i32()
Expand All @@ -219,7 +238,8 @@ pub extern "C" fn c_ret_i32() -> i32 {
0
}

// x86_64: i64 @c_ret_i64()
// x86_64-linux: i64 @c_ret_i64()
// x86_64-uefi: i64 @c_ret_i64()
// i686: i64 @c_ret_i64()
// aarch64-apple: i64 @c_ret_i64()
// aarch64-windows: i64 @c_ret_i64()
Expand Down
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