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Always generate GEP i8 / ptradd for struct offsets #121665

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merged 5 commits into from
Mar 4, 2024
Merged

Always generate GEP i8 / ptradd for struct offsets #121665

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123015e
always use gep inbounds i8 (ptradd) for field offsets
erikdesjardins Feb 24, 2024
beed25b
remove struct_gep, use manual layout calculations for va_arg
erikdesjardins Feb 24, 2024
4724cd4
introduce and use ptradd/inbounds_ptradd instead of gep
erikdesjardins Feb 24, 2024
c1017d4
use non-inbounds GEP for ZSTs, add fixmes
erikdesjardins Feb 28, 2024
4016510
test merging of multiple match branches that access fields of the sam…
erikdesjardins Feb 28, 2024
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use non-inbounds GEP for ZSTs, add fixmes
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@erikdesjardins
erikdesjardins committed Feb 28, 2024
commit c1017d48281c0fad0a93e36315db357d3a8b5f6a
5 changes: 5 additions & 0 deletions compiler/rustc_codegen_ssa/src/mir/place.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,10 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
let mut simple = || {
let llval = if offset.bytes() == 0 {
self.llval
} else if field.is_zst() {
// FIXME(erikdesjardins): it should be fine to use inbounds for ZSTs too;
// keeping this logic for now to preserve previous behavior.
bx.ptradd(self.llval, bx.const_usize(offset.bytes()))
} else {
bx.inbounds_ptradd(self.llval, bx.const_usize(offset.bytes()))
};
Expand Down Expand Up @@ -164,6 +168,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
debug!("struct_field_ptr: DST field offset: {:?}", offset);

// Adjust pointer.
// FIXME(erikdesjardins): should be able to use inbounds here too.
let ptr = bx.ptradd(self.llval, offset);

PlaceRef { llval: ptr, llextra: self.llextra, layout: field, align: effective_field_align }
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6 changes: 3 additions & 3 deletions tests/codegen/zst-offset.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ pub fn helper(_: usize) {
// CHECK-LABEL: @scalar_layout
#[no_mangle]
pub fn scalar_layout(s: &(u64, ())) {
// CHECK: getelementptr inbounds i8, {{.+}}, [[USIZE]] 8
// CHECK: getelementptr i8, {{.+}}, [[USIZE]] 8
let x = &s.1;
witness(&x); // keep variable in an alloca
}
Expand All @@ -22,7 +22,7 @@ pub fn scalar_layout(s: &(u64, ())) {
// CHECK-LABEL: @scalarpair_layout
#[no_mangle]
pub fn scalarpair_layout(s: &(u64, u32, ())) {
// CHECK: getelementptr inbounds i8, {{.+}}, [[USIZE]] 12
// CHECK: getelementptr i8, {{.+}}, [[USIZE]] 12
let x = &s.2;
witness(&x); // keep variable in an alloca
}
Expand All @@ -34,7 +34,7 @@ pub struct U64x4(u64, u64, u64, u64);
// CHECK-LABEL: @vector_layout
#[no_mangle]
pub fn vector_layout(s: &(U64x4, ())) {
// CHECK: getelementptr inbounds i8, {{.+}}, [[USIZE]] 32
// CHECK: getelementptr i8, {{.+}}, [[USIZE]] 32
let x = &s.1;
witness(&x); // keep variable in an alloca
}
Expand Down
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