From e585103306f5b69a62c71e8462dc78a8ef2da9f9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Wed, 28 Aug 2024 03:03:12 +0200
Subject: [PATCH] llvm: Disable FastISel on MIPS as a workaround for #21215.

Until llvm/llvm-project#106231 trickles down.
---
 src/codegen/llvm.zig          | 2 ++
 src/codegen/llvm/bindings.zig | 1 +
 src/zig_llvm.cpp              | 7 ++++++-
 src/zig_llvm.h                | 1 +
 4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index 57ee1c8a67..120618563e 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -1280,6 +1280,8 @@ pub const Object = struct {
             .tsan = options.sanitize_thread,
             .sancov = options.fuzz,
             .lto = options.lto,
+            // https://github.com/ziglang/zig/issues/21215
+            .allow_fast_isel = !comp.root_mod.resolved_target.result.cpu.arch.isMIPS(),
             .asm_filename = null,
             .bin_filename = options.bin_path,
             .llvm_ir_filename = options.post_ir_path,
diff --git a/src/codegen/llvm/bindings.zig b/src/codegen/llvm/bindings.zig
index a5017568e5..08c5b0b055 100644
--- a/src/codegen/llvm/bindings.zig
+++ b/src/codegen/llvm/bindings.zig
@@ -91,6 +91,7 @@ pub const TargetMachine = opaque {
         tsan: bool,
         sancov: bool,
         lto: bool,
+        allow_fast_isel: bool,
         asm_filename: ?[*:0]const u8,
         bin_filename: ?[*:0]const u8,
         llvm_ir_filename: ?[*:0]const u8,
diff --git a/src/zig_llvm.cpp b/src/zig_llvm.cpp
index b6b6d05f57..9465168dbd 100644
--- a/src/zig_llvm.cpp
+++ b/src/zig_llvm.cpp
@@ -258,7 +258,6 @@ ZIG_EXTERN_C bool ZigLLVMTargetMachineEmitToFile(LLVMTargetMachineRef targ_machi
                               options.bin_filename? options.bin_filename : options.asm_filename);
 
     TargetMachine &target_machine = *reinterpret_cast<TargetMachine*>(targ_machine_ref);
-    target_machine.setO0WantsFastISel(true);
 
     Module &llvm_module = *unwrap(module_ref);
 
@@ -369,6 +368,12 @@ ZIG_EXTERN_C bool ZigLLVMTargetMachineEmitToFile(LLVMTargetMachineRef targ_machi
         }
     }
 
+    if (options.allow_fast_isel) {
+        target_machine.setO0WantsFastISel(true);
+    } else {
+        target_machine.setFastISel(false);
+    }
+
     // Optimization phase
     module_pm.run(llvm_module, module_am);
 
diff --git a/src/zig_llvm.h b/src/zig_llvm.h
index cdc2adfb6d..0935c780ad 100644
--- a/src/zig_llvm.h
+++ b/src/zig_llvm.h
@@ -59,6 +59,7 @@ struct ZigLLVMEmitOptions {
     bool tsan;
     bool sancov;
     bool lto;
+    bool allow_fast_isel;
     const char *asm_filename;
     const char *bin_filename;
     const char *llvm_ir_filename;