From 25f1d0906d2b5a8276c3832783970a798c12cc6c Mon Sep 17 00:00:00 2001
From: Laytan Laats <laytanlaats@hotmail.com>
Date: Wed, 1 May 2024 22:12:37 +0200
Subject: compiler: improve target features support

---
 src/llvm_backend.cpp | 104 ++++++++++++++++++++++-----------------------------
 1 file changed, 45 insertions(+), 59 deletions(-)

(limited to 'src/llvm_backend.cpp')

diff --git a/src/llvm_backend.cpp b/src/llvm_backend.cpp
index 4b94cf020..fad130b99 100644
--- a/src/llvm_backend.cpp
+++ b/src/llvm_backend.cpp
@@ -41,6 +41,37 @@ String get_default_microarchitecture() {
 	return default_march;
 }
 
+String get_final_microarchitecture() {
+	BuildContext *bc = &build_context;
+
+	String microarch = bc->microarch;
+	if (microarch.len == 0) {
+		microarch = get_default_microarchitecture();
+	} else if (microarch == str_lit("native")) {
+		microarch = make_string_c(LLVMGetHostCPUName());
+	}
+	return microarch;
+}
+
+gb_internal String get_default_features() {
+	BuildContext *bc = &build_context;
+
+	int off = 0;
+	for (int i = 0; i < bc->metrics.arch; i += 1) {
+		off += target_microarch_counts[i];
+	}
+
+	String microarch = get_final_microarchitecture();
+	for (int i = off; i < off+target_microarch_counts[bc->metrics.arch]; i += 1) {
+		if (microarch_features_list[i].microarch == microarch) {
+			return microarch_features_list[i].features;
+		}
+	}
+
+	GB_PANIC("unknown microarch");
+	return {};
+}
+
 gb_internal void lb_add_foreign_library_path(lbModule *m, Entity *e) {
 	if (e == nullptr) {
 		return;
@@ -2468,69 +2499,24 @@ gb_internal bool lb_generate_code(lbGenerator *gen) {
 		code_mode = LLVMCodeModelKernel;
 	}
 
-	String      host_cpu_name = copy_string(permanent_allocator(), make_string_c(LLVMGetHostCPUName()));
-	String      llvm_cpu      = get_default_microarchitecture();
-	char const *llvm_features = "";
-	if (build_context.microarch.len != 0) {
-		if (build_context.microarch == "native") {
-			llvm_cpu = host_cpu_name;
-		} else {
-			llvm_cpu = copy_string(permanent_allocator(), build_context.microarch);
-		}
-		if (llvm_cpu == host_cpu_name) {
-			llvm_features = LLVMGetHostCPUFeatures();
+	String llvm_cpu = get_final_microarchitecture();
+
+	gbString llvm_features = gb_string_make(temporary_allocator(), "");
+	String_Iterator it = {build_context.target_features_string, 0};
+	bool first = true;
+	for (;;) {
+		String str = string_split_iterator(&it, ',');
+		if (str == "") break;
+		if (!first) {
+			llvm_features = gb_string_appendc(llvm_features, ",");
 		}
-	}
+		first = false;
 
-	// NOTE(Jeroen): Uncomment to get the list of supported microarchitectures.
-	/*
-	if (build_context.microarch == "?") {
-		string_set_add(&build_context.target_features_set, str_lit("+cpuhelp"));
+		llvm_features = gb_string_appendc(llvm_features, "+");
+		llvm_features = gb_string_append_length(llvm_features, str.text, str.len);
 	}
-	*/
 
-	if (build_context.target_features_set.entries.count != 0) {
-		// 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;
-		}
-	}
+	debugf("CPU: %.*s, Features: %s\n", LIT(llvm_cpu), llvm_features);	
 
 	// GB_ASSERT_MSG(LLVMTargetHasAsmBackend(target));
 
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