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Auto merge of #122050 - erikdesjardins:sret, r=nikic

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Stop using LLVM struct types for byval/sret

For `byval` and `sret`, the type has no semantic meaning, only the size matters\*†. Using `[N x i8]` is a more direct way to specify that we want `N` bytes, and avoids relying on LLVM's struct layout.

\*: The alignment would matter, if we didn't explicitly specify it. From what I can tell, we always specified the alignment for `sret`; for `byval`, we didn't until #112157.

†: For `byval`, the hidden copy may be impacted by padding in the LLVM struct type, i.e. padding bytes may not be copied. (I'm not sure if this is done today, but I think it would be legal.) But we manually pad our LLVM struct types specifically to avoid there ever being LLVM-visible padding, so that shouldn't be an issue.

Split out from #121577.

r? `@nikic`
This commit is contained in:
bors 2024-03-11 04:45:27 +00:00
commit a6d93acf5f
17 changed files with 327 additions and 130 deletions
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20
compiler/rustc_codegen_llvm/src/abi.rs
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@ -424,7 +424,10 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
PassMode::Indirect { attrs, meta_attrs: _, on_stack } => {
assert!(!on_stack);
let i = apply(attrs);
let sret = llvm::CreateStructRetAttr(cx.llcx, self.ret.layout.llvm_type(cx));
let sret = llvm::CreateStructRetAttr(
cx.llcx,
cx.type_array(cx.type_i8(), self.ret.layout.size.bytes()),
);
attributes::apply_to_llfn(llfn, llvm::AttributePlace::Argument(i), &[sret]);
}
PassMode::Cast { cast, pad_i32: _ } => {
@ -437,7 +440,10 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
PassMode::Ignore => {}
PassMode::Indirect { attrs, meta_attrs: None, on_stack: true } => {
let i = apply(attrs);
let byval = llvm::CreateByValAttr(cx.llcx, arg.layout.llvm_type(cx));
let byval = llvm::CreateByValAttr(
cx.llcx,
cx.type_array(cx.type_i8(), arg.layout.size.bytes()),
);
attributes::apply_to_llfn(llfn, llvm::AttributePlace::Argument(i), &[byval]);
}
PassMode::Direct(attrs)
@ -486,7 +492,10 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
PassMode::Indirect { attrs, meta_attrs: _, on_stack } => {
assert!(!on_stack);
let i = apply(bx.cx, attrs);
let sret = llvm::CreateStructRetAttr(bx.cx.llcx, self.ret.layout.llvm_type(bx));
let sret = llvm::CreateStructRetAttr(
bx.cx.llcx,
bx.cx.type_array(bx.cx.type_i8(), self.ret.layout.size.bytes()),
);
attributes::apply_to_callsite(callsite, llvm::AttributePlace::Argument(i), &[sret]);
}
PassMode::Cast { cast, pad_i32: _ } => {
@ -513,7 +522,10 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
PassMode::Ignore => {}
PassMode::Indirect { attrs, meta_attrs: None, on_stack: true } => {
let i = apply(bx.cx, attrs);
let byval = llvm::CreateByValAttr(bx.cx.llcx, arg.layout.llvm_type(bx));
let byval = llvm::CreateByValAttr(
bx.cx.llcx,
bx.cx.type_array(bx.cx.type_i8(), arg.layout.size.bytes()),
);
attributes::apply_to_callsite(
callsite,
llvm::AttributePlace::Argument(i),