0becc89d4a
alignment of `byval` on x86 in the process.
Commit 88e4d2c291 from five years ago removed
support for alignment on indirectly-passed arguments because of problems with
the `i686-pc-windows-msvc` target. Unfortunately, the `memcpy` optimizations I
recently added to LLVM 16 depend on this to forward `memcpy`s. This commit
attempts to fix the problems with `byval` parameters on that target and now
correctly adds the `align` attribute.
The problem is summarized in [this comment] by @eddyb. Briefly, 32-bit x86 has
special alignment rules for `byval` parameters: for the most part, their
alignment is forced to 4. This is not well-documented anywhere but in the Clang
source. I looked at the logic in Clang `TargetInfo.cpp` and tried to replicate
it here. The relevant methods in that file are
`X86_32ABIInfo::getIndirectResult()` and
`X86_32ABIInfo::getTypeStackAlignInBytes()`. The `align` parameter attribute
for `byval` parameters in LLVM must match the platform ABI, or miscompilations
will occur. Note that this doesn't use the approach suggested by eddyb, because
I felt it was overkill to store the alignment in `on_stack` when special
handling is really only needed for 32-bit x86.
As a side effect, this should fix #80127, because it will make the `align`
parameter attribute for `byval` parameters match the platform ABI on LLVM
x86-64.
[this comment]: https://github.com/rust-lang/rust/pull/80822#issuecomment-829985417
70 lines
1.6 KiB
Rust
70 lines
1.6 KiB
Rust
// compile-flags: -C opt-level=0 -C no-prepopulate-passes
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// This test checks that arguments/returns in opt-level=0 builds,
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// while lacking attributes used for optimization, still have ABI-affecting attributes.
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#![crate_type = "lib"]
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#![feature(rustc_attrs)]
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pub struct S {
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_field: [i32; 8],
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}
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// CHECK: zeroext i1 @boolean(i1 zeroext %x)
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#[no_mangle]
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pub fn boolean(x: bool) -> bool {
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x
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}
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// CHECK-LABEL: @boolean_call
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#[no_mangle]
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pub fn boolean_call(x: bool, f: fn(bool) -> bool) -> bool {
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// CHECK: call zeroext i1 %f(i1 zeroext %x)
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f(x)
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}
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// CHECK: align 4 {{i32\*|ptr}} @borrow({{i32\*|ptr}} align 4 %x)
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#[no_mangle]
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pub fn borrow(x: &i32) -> &i32 {
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x
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}
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// CHECK: align 4 {{i32\*|ptr}} @borrow_mut({{i32\*|ptr}} align 4 %x)
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#[no_mangle]
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pub fn borrow_mut(x: &mut i32) -> &mut i32 {
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x
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}
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// CHECK-LABEL: @borrow_call
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#[no_mangle]
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pub fn borrow_call(x: &i32, f: fn(&i32) -> &i32) -> &i32 {
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// CHECK: call align 4 {{i32\*|ptr}} %f({{i32\*|ptr}} align 4 %x)
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f(x)
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}
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// CHECK: void @struct_({{%S\*|ptr}} sret(%S) align 4{{( %_0)?}}, {{%S\*|ptr}} align 4 %x)
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#[no_mangle]
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pub fn struct_(x: S) -> S {
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x
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}
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// CHECK-LABEL: @struct_call
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#[no_mangle]
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pub fn struct_call(x: S, f: fn(S) -> S) -> S {
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// CHECK: call void %f({{%S\*|ptr}} sret(%S) align 4{{( %_0)?}}, {{%S\*|ptr}} align 4 %{{.+}})
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f(x)
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}
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// CHECK: { i8, i8 } @enum_(i1 zeroext %x.0, i8 %x.1)
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#[no_mangle]
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pub fn enum_(x: Option<u8>) -> Option<u8> {
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x
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}
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// CHECK-LABEL: @enum_call
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#[no_mangle]
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pub fn enum_call(x: Option<u8>, f: fn(Option<u8>) -> Option<u8>) -> Option<u8> {
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// CHECK: call { i8, i8 } %f(i1 zeroext %x.0, i8 %x.1)
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f(x)
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}
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