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fix SysV vector ABI: 64-bit slot width, wide-vector return, wrapped-vector return

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kalsprite
2026-08-13 21:30:36 -07:00
parent 88c194379c
commit 1cf1c4103e
1 changed files with 25 additions and 6 deletions
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31
src/llvm_abi.cpp
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@@ -795,12 +795,18 @@ namespace lbAbiAmd64SysV {
}
}
if (is_arg && cls.count > 2 && is_sse(cls[0])) {
if (cls.count > 2 && is_sse(cls[0])) {
// An SSE run wider than two eightbytes has no register to land in at
// the baseline ISA, so as an argument it goes to memory, bare vector
// or struct-wrapped. The return does not: clang returns it by value
// and lets LLVM split it across xmm0:xmm1.
return lb_arg_type_indirect_byval(c, type, source_type);
// the baseline ISA. It goes to memory, bare vector or struct-wrapped.
// A bare vector RETURN is the one exception: it is not an aggregate.
// Clang gives it no hidden pointer and lets LLVM split it across
// xmm0:xmm1, but the struct that wraps it still gets one.
if (is_arg) {
return lb_arg_type_indirect_byval(c, type, source_type);
}
if (LLVMGetTypeKind(type) != LLVMVectorTypeKind) {
all_mem(&cls);
}
}
if (is_register(type)) {
LLVMAttributeRef attribute = nullptr;
@@ -978,7 +984,11 @@ namespace lbAbiAmd64SysV {
i64 sz = lb_sizeof(t);
i64 words = (sz + 7)/8;
auto reg_classes = array_make<RegClass>(heap_allocator(), cast(isize)words);
if (words > 4) {
if (words > 4 && LLVMGetTypeKind(t) != LLVMVectorTypeKind) {
// A BARE vector is exempt: it is not an aggregate. Clang never gives it
// a hidden pointer however wide it is. `<16 x float>` is returned directly
// and split across xmm0-xmm3, and the SSE run below still sends it to
// memory as an ARGUMENT.
all_mem(&reg_classes);
} else {
bool from_source = source_type != nullptr && source_is_classifiable(source_type) &&
@@ -1143,6 +1153,15 @@ namespace lbAbiAmd64SysV {
}
i64 sz = lb_sizeof(type);
if (LLVMGetTypeKind(type) == LLVMVectorTypeKind && sz == 8 &&
reg_classes.count == 1 && is_sse(reg_classes[0])) {
// LLVM rounds a bare vector's stack slot up to the legal vector width.
// An 8-byte one takes 16 bytes where the ABI wants 8. clang coerces every
// 64-bit vector to `double`, which lands in the same half of the same xmm
// and takes one eightbyte on the stack.
array_free(&types);
return LLVMDoubleTypeInContext(c);
}
if (all_ints) {
for_array(i, reg_classes) {
GB_ASSERT(sz > 0);