From 07114e6bc69106fb77beb879a8a2f78a4ba4b256 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Mon, 30 Jun 2025 07:01:35 +0200
Subject: [PATCH] llvm: Disable the machine outliner pass on RISC-V

---
 src/codegen/llvm.zig          |  3 +++
 src/codegen/llvm/bindings.zig |  1 +
 src/zig_llvm.cpp              | 16 ++++++++++------
 src/zig_llvm.h                |  1 +
 4 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index a48fb68352..a5e6d35fd6 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -1068,6 +1068,9 @@ pub const Object = struct {
                 .full => .FullPreLink,
             },
             .allow_fast_isel = true,
+            // LLVM's RISC-V backend for some reason enables the machine outliner by default even
+            // though it's clearly not ready and produces multiple miscompilations in our std tests.
+            .allow_machine_outliner = !comp.root_mod.resolved_target.result.cpu.arch.isRISCV(),
             .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 44ca599fdc..5d2d4c2a99 100644
--- a/src/codegen/llvm/bindings.zig
+++ b/src/codegen/llvm/bindings.zig
@@ -92,6 +92,7 @@ pub const TargetMachine = opaque {
         sancov: bool,
         lto: LtoPhase,
         allow_fast_isel: bool,
+        allow_machine_outliner: 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 cb624ea256..fe4e421dc3 100644
--- a/src/zig_llvm.cpp
+++ b/src/zig_llvm.cpp
@@ -260,6 +260,16 @@ ZIG_EXTERN_C bool ZigLLVMTargetMachineEmitToFile(LLVMTargetMachineRef targ_machi
 
     TargetMachine &target_machine = *reinterpret_cast<TargetMachine*>(targ_machine_ref);
 
+    if (options->allow_fast_isel) {
+        target_machine.setO0WantsFastISel(true);
+    } else {
+        target_machine.setFastISel(false);
+    }
+
+    if (!options->allow_machine_outliner) {
+        target_machine.setMachineOutliner(false);
+    }
+
     Module &llvm_module = *unwrap(module_ref);
 
     // Pipeline configurations
@@ -385,12 +395,6 @@ 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 f75e119988..e2dba338c3 100644
--- a/src/zig_llvm.h
+++ b/src/zig_llvm.h
@@ -71,6 +71,7 @@ struct ZigLLVMEmitOptions {
     bool sancov;
     ZigLLVMThinOrFullLTOPhase lto;
     bool allow_fast_isel;
+    bool allow_machine_outliner;
     const char *asm_filename;
     const char *bin_filename;
     const char *llvm_ir_filename;