kit

commit cec5aeab9c5d70fee51c0e90ae8cf9f673fade85
parent 04a7d100199049a9550ce78eaee8a5835c571c64
Author: Ryan Sepassi <rsepassi@gmail.com>
Date:   Mon, 18 May 2026 21:19:28 -0700

Fix x64 atomic compare-exchange register pressure

Diffstat:
M
src/api/cg.c
 | 
36
+++++++++++++++++++++++++++++++++---

1 file changed, 33 insertions(+), 3 deletions(-)
diff --git a/src/api/cg.c b/src/api/cg.c
@@ -4421,6 +4421,33 @@ void cfree_cg_atomic_rmw(CfreeCg *g, CfreeCgMemAccess access,
   api_push(g, api_make_sv(dst, val_ty));
 }
 
+static int api_take_dead_owned_reg(ApiSValue *sv, u8 cls, Reg avoid, Reg *out) {
+  Reg r;
+  if (sv->res != RES_REG || sv->pinned)
+    return 0;
+  if (api_class_of_sv(sv) != cls)
+    return 0;
+  r = api_reg_of_sv(sv);
+  if (r == (Reg)REG_NONE || r == avoid)
+    return 0;
+  sv->res = RES_INHERENT;
+  *out = r;
+  return 1;
+}
+
+static Reg api_alloc_dead_input_or_spill(CfreeCg *g, ApiSValue *a,
+                                         ApiSValue *b, ApiSValue *c, u8 cls,
+                                         CfreeCgTypeId ty, Reg avoid) {
+  Reg r;
+  if (api_take_dead_owned_reg(a, cls, avoid, &r))
+    return r;
+  if (api_take_dead_owned_reg(b, cls, avoid, &r))
+    return r;
+  if (api_take_dead_owned_reg(c, cls, avoid, &r))
+    return r;
+  return api_alloc_reg_or_spill(g, cls, ty);
+}
+
 void cfree_cg_atomic_cmpxchg(CfreeCg *g, CfreeCgMemAccess access,
                              CfreeCgMemOrder success, CfreeCgMemOrder failure,
                              int weak) {
@@ -4444,7 +4471,6 @@ void cfree_cg_atomic_cmpxchg(CfreeCg *g, CfreeCgMemAccess access,
                             api_sv_type(&expected));
   api_validate_memory_value(g, "atomic_cmpxchg desired", val_ty,
                             api_sv_type(&desired));
-  bool_ty = builtin_id(CFREE_CG_BUILTIN_BOOL);
   addr = api_force_reg(g, &ptr, pty);
   exp_op = api_sv_op_is_reg_or_imm(&expected)
                ? expected.op
@@ -4452,8 +4478,12 @@ void cfree_cg_atomic_cmpxchg(CfreeCg *g, CfreeCgMemAccess access,
   des_op = api_sv_op_is_reg_or_imm(&desired)
                ? desired.op
                : api_force_reg(g, &desired, val_ty);
-  pr = api_alloc_reg_or_spill(g, api_type_class(val_ty), val_ty);
-  kr = api_alloc_reg_or_spill(g, RC_INT, bool_ty);
+  bool_ty = builtin_id(CFREE_CG_BUILTIN_BOOL);
+  pr = api_alloc_dead_input_or_spill(g, &ptr, &expected, &desired,
+                                     api_type_class(val_ty), val_ty,
+                                     (Reg)REG_NONE);
+  kr = api_alloc_dead_input_or_spill(g, &ptr, &expected, &desired, RC_INT,
+                                     bool_ty, pr);
   prior = api_op_reg(pr, val_ty);
   ok = api_op_reg(kr, bool_ty);
   g->target->atomic_cas(g->target, prior, ok, addr, exp_op, des_op,