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src: enable_target_feature should add features, not overwrite

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`llvm_features` being empty is the default state, and implies the
presence of certain features.

Previously if any target features were explicitly enabled by the
`enable_target_feature` attribute, they were added comma separated
to `llvm_features`.

For example: `lzcnt,popcnt,...,sse4.2,sse`

This was causing LLVM to try to target a CPU that *ONLY* has the
explicitly enabled features.  This now will prefix explicitly enabled
features with a `+`, and preserve the existing `llvm_features` string
by appending to it if it is set.
This commit is contained in:
Yawning Angel
2023-12-15 17:29:59 +09:00
parent 9235e82451
commit cd65a15d81
2 changed files with 43 additions and 2 deletions
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src/llvm_backend.cpp
+40 -1
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@@ -2531,7 +2531,46 @@ gb_internal bool lb_generate_code(lbGenerator *gen) {
*/
if (build_context.target_features_set.entries.count != 0) {
llvm_features = target_features_set_to_cstring(permanent_allocator(), false);
// Prefix all of the features with a `+`, because we are
// enabling additional features.
char const *additional_features = target_features_set_to_cstring(permanent_allocator(), false, true);
String f_string = make_string_c(llvm_features);
String a_string = make_string_c(additional_features);
isize f_len = f_string.len;
if (f_len == 0) {
// The common case is that llvm_features is empty, so
// the target_features_set additions can be used as is.
llvm_features = additional_features;
} else {
// The user probably specified `-microarch:native`, so
// llvm_features is populated by LLVM's idea of what
// the host CPU supports.
//
// As far as I can tell, (which is barely better than
// wild guessing), a bitset is formed by parsing the
// string left to right.
//
// So, llvm_features + ',' + additonal_features, will
// makes the target_features_set override llvm_features.
char *tmp = gb_alloc_array(permanent_allocator(), char, f_len + 1 + a_string.len + 1);
isize len = 0;
// tmp = f_string
gb_memmove(tmp, f_string.text, f_string.len);
len += f_string.len;
// tmp += ','
tmp[len++] = ',';
// tmp += a_string
gb_memmove(tmp + len, a_string.text, a_string.len);
len += a_string.len;
// tmp += NUL
tmp[len++] = 0;
llvm_features = tmp;
}
}
// GB_ASSERT_MSG(LLVMTargetHasAsmBackend(target));