Commit f03d54f0692967872f6d5664597d3e349d79c2a3 | zig

author	Alex Rønne Petersen <alex@alexrp.com> 2024-07-29 20:26:39+02:00
committer	Andrew Kelley <andrew@ziglang.org> 2024-08-01 01:07:56-07:00
log	f03d54f0692967872f6d5664597d3e349d79c2a3
tree	a53cf0543f7a310f05e29d49c9abd252e1b24293
parent	604e87a95868094bdddbcc6a4579f8535ae5e2a9

std.atomic: Don't lie to the compiler about memory clobbers in spinLoopHint().

1 files changed, 8 insertions(+), 16 deletions(-)

lib
- std
  - atomic.zig

lib/std/atomic.zig+8-16

 @@ -380,7 +380,7 @@ pub inline fn spinLoopHint() void {
         // https://software.intel.com/content/www/us/en/develop/articles/benefitting-power-and-performance-sleep-loops.html
         .x86,
         .x86_64,
-        => asm volatile ("pause" ::: "memory"),
+        => asm volatile ("pause"),
         // No-op instruction that serves as a hardware-thread resource yield hint.
         // https://stackoverflow.com/a/7588941
 @@ -388,7 +388,7 @@ pub inline fn spinLoopHint() void {
         .powerpcle,
         .powerpc64,
         .powerpc64le,
-        => asm volatile ("or 27, 27, 27" ::: "memory"),
+        => asm volatile ("or 27, 27, 27"),
         // `isb` appears more reliable for releasing execution resources than `yield`
         // on common aarch64 CPUs.
 @@ -396,7 +396,7 @@ pub inline fn spinLoopHint() void {
         // https://bugs.mysql.com/bug.php?id=100664
         .aarch64,
         .aarch64_be,
-        => asm volatile ("isb" ::: "memory"),
+        => asm volatile ("isb"),
         // `yield` was introduced in v6k but is also available on v6m.
         // https://www.keil.com/support/man/docs/armasm/armasm_dom1361289926796.htm
 @@ -409,30 +409,22 @@ pub inline fn spinLoopHint() void {
                 .has_v6k, .has_v6m,
             });
             if (can_yield) {
-                asm volatile ("yield" ::: "memory");
+                asm volatile ("yield");
-            } else {
-                asm volatile ("" ::: "memory");
             }
         },
         // The 8-bit immediate specifies the amount of cycles to pause for. We can't really be too
         // opinionated here.
         .hexagon,
-        => asm volatile ("pause(#1)" ::: "memory"),
+        => asm volatile ("pause(#1)"),
         .riscv32,
         .riscv64,
-        => {
+        => if (comptime std.Target.riscv.featureSetHas(builtin.target.cpu.features, .zihintpause)) {
-            if (comptime std.Target.riscv.featureSetHas(builtin.target.cpu.features, .zihintpause)) {
+            asm volatile ("pause");
-                asm volatile ("pause" ::: "memory");
-            } else {
-                asm volatile ("" ::: "memory");
-            }
         },
-        // Memory barrier to prevent the compiler from optimizing away the spin-loop
+        else => {},
-        // even if no hint_instruction was provided.
-        else => asm volatile ("" ::: "memory"),
     }
 }