From 19691c0b174f283ffe5b6c3fe8533ef458736064 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Wed, 15 Sep 2021 12:37:32 -0700
Subject: stage2: implement `@fence`

---
 src/codegen/c.zig             | 12 ++++++++++++
 src/codegen/llvm.zig          |  9 +++++++++
 src/codegen/llvm/bindings.zig |  8 ++++++++
 3 files changed, 29 insertions(+)

(limited to 'src/codegen')

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index ff49b18f7b..a2e2d7b20d 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -842,6 +842,7 @@ fn genBody(o: *Object, body: []const Air.Inst.Index) error{ AnalysisFail, OutOfM
 
             .breakpoint => try airBreakpoint(o),
             .unreach    => try airUnreach(o),
+            .fence      => try airFence(o, inst),
 
             // TODO use a different strategy for add that communicates to the optimizer
             // that wrapping is UB.
@@ -1439,6 +1440,17 @@ fn airBreakpoint(o: *Object) !CValue {
     return CValue.none;
 }
 
+fn airFence(o: *Object, inst: Air.Inst.Index) !CValue {
+    const atomic_order = o.air.instructions.items(.data)[inst].fence;
+    const writer = o.writer();
+
+    try writer.writeAll("zig_fence(");
+    try writeMemoryOrder(writer, atomic_order);
+    try writer.writeAll(");\n");
+
+    return CValue.none;
+}
+
 fn airUnreach(o: *Object) !CValue {
     try o.writer().writeAll("zig_unreachable();\n");
     return CValue.none;
diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index b28c371466..569f857caa 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -1059,6 +1059,7 @@ pub const FuncGen = struct {
                 .array_to_slice => try self.airArrayToSlice(inst),
                 .cmpxchg_weak   => try self.airCmpxchg(inst, true),
                 .cmpxchg_strong => try self.airCmpxchg(inst, false),
+                .fence          => try self.airFence(inst),
 
                 .struct_field_ptr => try self.airStructFieldPtr(inst),
                 .struct_field_val => try self.airStructFieldVal(inst),
@@ -2005,6 +2006,14 @@ pub const FuncGen = struct {
         return null;
     }
 
+    fn airFence(self: *FuncGen, inst: Air.Inst.Index) !?*const llvm.Value {
+        const atomic_order = self.air.instructions.items(.data)[inst].fence;
+        const llvm_memory_order = toLlvmAtomicOrdering(atomic_order);
+        const single_threaded = llvm.Bool.fromBool(self.single_threaded);
+        _ = self.builder.buildFence(llvm_memory_order, single_threaded, "");
+        return null;
+    }
+
     fn airCmpxchg(self: *FuncGen, inst: Air.Inst.Index, is_weak: bool) !?*const llvm.Value {
         const ty_pl = self.air.instructions.items(.data)[inst].ty_pl;
         const extra = self.air.extraData(Air.Cmpxchg, ty_pl.payload).data;
diff --git a/src/codegen/llvm/bindings.zig b/src/codegen/llvm/bindings.zig
index b4bd91708d..3fed3ca879 100644
--- a/src/codegen/llvm/bindings.zig
+++ b/src/codegen/llvm/bindings.zig
@@ -522,6 +522,14 @@ pub const Builder = opaque {
         Else: *const Value,
         Name: [*:0]const u8,
     ) *const Value;
+
+    pub const buildFence = LLVMBuildFence;
+    extern fn LLVMBuildFence(
+        B: *const Builder,
+        ordering: AtomicOrdering,
+        singleThread: Bool,
+        Name: [*:0]const u8,
+    ) *const Value;
 };
 
 pub const IntPredicate = enum(c_uint) {
-- 
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