From 35d6ee08c468642969b594b711dd6448bbaefa89 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 17 Mar 2022 19:03:37 -0700
Subject: [PATCH] stage2: default to LLVM backend

on targets for which self-hosted backends are not up to par.

See #89
---
 src/Compilation.zig | 13 ++++++++++---
 src/target.zig      |  9 +++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/src/Compilation.zig b/src/Compilation.zig
index c3d349b527..f6fe452951 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -943,11 +943,18 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             if (use_stage1)
                 break :blk true;
 
-            // Prefer LLVM for release builds as long as it supports the target architecture.
-            if (options.optimize_mode != .Debug and target_util.hasLlvmSupport(options.target))
+            // If LLVM does not support the target, then we can't use it.
+            if (!target_util.hasLlvmSupport(options.target))
+                break :blk false;
+
+            // Prefer LLVM for release builds.
+            if (options.optimize_mode != .Debug)
                 break :blk true;
 
-            break :blk false;
+            // At this point we would prefer to use our own self-hosted backend,
+            // because the compilation speed is better than LLVM. But only do it if
+            // we are confident in the robustness of the backend.
+            break :blk !target_util.selfHostedBackendIsAsRobustAsLlvm(options.target);
         };
         if (!use_llvm) {
             if (options.use_llvm == true) {
diff --git a/src/target.zig b/src/target.zig
index aec37b6394..2eff4f8445 100644
--- a/src/target.zig
+++ b/src/target.zig
@@ -268,6 +268,15 @@ pub fn hasLlvmSupport(target: std.Target) bool {
     };
 }
 
+/// The set of targets that our own self-hosted backends have robust support for.
+/// Used to select between LLVM backend and self-hosted backend when compiling in
+/// debug mode. A given target should only return true here if it is passing greater
+/// than or equal to the number of behavior tests as the respective LLVM backend.
+pub fn selfHostedBackendIsAsRobustAsLlvm(target: std.Target) bool {
+    _ = target;
+    return false;
+}
+
 pub fn supportsStackProbing(target: std.Target) bool {
     return target.os.tag != .windows and target.os.tag != .uefi and
         (target.cpu.arch == .i386 or target.cpu.arch == .x86_64);