lego_jit_is(true|false)_s.patch

diff --git src/core/coerce.c src/core/coerce.c
index 021e77073..87f67acf0 100644
--- src/core/coerce.c
+++ src/core/coerce.c
@@ -14,8 +14,11 @@ typedef struct {
     MVMRegister  res_reg;
 } BoolMethReturnData;
 
-MVMint64 MVM_coerce_istrue_s(MVMThreadContext *tc, MVMString *str) {
-    return str == NULL || !IS_CONCRETE(str) || MVM_string_graphs_nocheck(tc, str) == 0 ? 0 : 1;
+MVMint64 MVM_coerce_istrue_s(MVMThreadContext *tc, MVMString *str, MVMuint8 flip) {
+    MVMint64 result = str == NULL || !IS_CONCRETE(str) || MVM_string_graphs_nocheck(tc, str) == 0 ? 0 : 1;
+    if (flip)
+        result = result ? 0 : 1;
+    return result;
 }
 
 /* Tries to do the boolification. It may be that a method call is needed. In
@@ -76,7 +79,7 @@ void MVM_coerce_istrue(MVMThreadContext *tc, MVMObject *obj, MVMRegister *res_re
                     break;
                 }
                 str = REPR(obj)->box_funcs.get_str(tc, STABLE(obj), obj, OBJECT_BODY(obj));
-                result = MVM_coerce_istrue_s(tc, str);
+                result = MVM_coerce_istrue_s(tc, str, 0);
                 break;
             }
             case MVM_BOOL_MODE_UNBOX_STR_NOT_EMPTY_OR_ZERO: {
diff --git src/core/coerce.h src/core/coerce.h
index b5c3b69c7..66bcced0c 100644
--- src/core/coerce.h
+++ src/core/coerce.h
@@ -1,5 +1,5 @@
 /* Boolification. */
-MVMint64 MVM_coerce_istrue_s(MVMThreadContext *tc, MVMString *str);
+MVMint64 MVM_coerce_istrue_s(MVMThreadContext *tc, MVMString *str, MVMuint8 flip);
 void MVM_coerce_istrue(MVMThreadContext *tc, MVMObject *obj, MVMRegister *res_reg,
     MVMuint8 *true_addr, MVMuint8 *false_addr, MVMuint8 flip);
 
diff --git src/core/interp.c src/core/interp.c
index a36f46a4f..1da36f1db 100644
--- src/core/interp.c
+++ src/core/interp.c
@@ -320,7 +320,7 @@ void MVM_interp_run(MVMThreadContext *tc, void (*initial_invoke)(MVMThreadContex
             }
             OP(if_s0): {
                 MVMString *str = GET_REG(cur_op, 0).s;
-                if (!MVM_coerce_istrue_s(tc, str))
+                if (MVM_coerce_istrue_s(tc, str, 1))
                     cur_op += 6;
                 else
                     cur_op = bytecode_start + GET_UI32(cur_op, 2);
@@ -329,7 +329,7 @@ void MVM_interp_run(MVMThreadContext *tc, void (*initial_invoke)(MVMThreadContex
             }
             OP(unless_s0): {
                 MVMString *str = GET_REG(cur_op, 0).s;
-                if (!MVM_coerce_istrue_s(tc, str))
+                if (MVM_coerce_istrue_s(tc, str, 1))
                     cur_op = bytecode_start + GET_UI32(cur_op, 2);
                 else
                     cur_op += 6;
@@ -1843,11 +1843,11 @@ void MVM_interp_run(MVMThreadContext *tc, void (*initial_invoke)(MVMThreadContex
                 cur_op += 6;
                 goto NEXT;
             OP(istrue_s):
-                GET_REG(cur_op, 0).i64 = MVM_coerce_istrue_s(tc, GET_REG(cur_op, 2).s);
+                GET_REG(cur_op, 0).i64 = MVM_coerce_istrue_s(tc, GET_REG(cur_op, 2).s, 0);
                 cur_op += 4;
                 goto NEXT;
             OP(isfalse_s):
-                GET_REG(cur_op, 0).i64 = MVM_coerce_istrue_s(tc, GET_REG(cur_op, 2).s) ? 0 : 1;
+                GET_REG(cur_op, 0).i64 = MVM_coerce_istrue_s(tc, GET_REG(cur_op, 2).s, 1);
                 cur_op += 4;
                 goto NEXT;
             OP(null):
diff --git src/jit/core_templates.expr src/jit/core_templates.expr
index bf5e28c86..b33a63093 100644
--- src/jit/core_templates.expr
+++ src/jit/core_templates.expr
@@ -755,15 +755,15 @@
   (call (^func &MVM_coerce_istrue_s)
     (arglist
       (carg (tc) ptr)
-      (carg $1 ptr)) int_sz))
+      (carg $1 ptr)
+      (carg (^zero) int)) int_sz))
 
 (template: isfalse_s
-  (flagval
-    (zr
-      (call (^func &MVM_coerce_istrue_s)
-        (arglist
-          (carg (tc) ptr)
-          (carg $1 ptr)) int_sz))))
+  (call (^func &MVM_coerce_istrue_s)
+    (arglist
+      (carg (tc) ptr)
+      (carg $1 ptr)
+      (carg (^one) int)) int_sz))
 
 (template: null (^vmnull))
 
diff --git src/jit/graph.c src/jit/graph.c
index 0747d938a..5d0e82f8e 100644
--- src/jit/graph.c
+++ src/jit/graph.c
@@ -159,6 +159,7 @@ static void * op_to_func(MVMThreadContext *tc, MVMint16 opcode) {
     case MVM_OP_unbox_s: return MVM_repr_get_str;
     case MVM_OP_unbox_n: return MVM_repr_get_num;
     case MVM_OP_istrue: case MVM_OP_isfalse: return MVM_coerce_istrue;
+    case MVM_OP_istrue_s: case MVM_OP_isfalse_s: return MVM_coerce_istrue_s;
     case MVM_OP_istype: return MVM_6model_istype;
     case MVM_OP_isint: case MVM_OP_isnum: case MVM_OP_isstr: /* continued */
     case MVM_OP_islist: case MVM_OP_ishash: return MVM_repr_compare_repr_id;
@@ -2276,6 +2277,16 @@ start:
         jg_append_call_c(tc, jg, op_to_func(tc, op), 6, args, MVM_JIT_RV_VOID, -1);
         break;
     }
+    case MVM_OP_isfalse_s:
+    case MVM_OP_istrue_s: {
+        MVMint16 result = ins->operands[0].reg.orig;
+        MVMint16 str    = ins->operands[1].reg.orig;
+        MVMJitCallArg args[] = { { MVM_JIT_INTERP_VAR, { MVM_JIT_INTERP_TC } },
+                                 { MVM_JIT_REG_VAL, { str } },
+                                 { MVM_JIT_LITERAL, { op == MVM_OP_isfalse_s } }};
+        jg_append_call_c(tc, jg, op_to_func(tc, op), 3, args, MVM_JIT_RV_INT, result);
+        break;
+    }
     case MVM_OP_capturelex: {
         MVMint16 code = ins->operands[0].reg.orig;
         MVMJitCallArg args[] = { { MVM_JIT_INTERP_VAR, { MVM_JIT_INTERP_TC } },
diff --git src/jit/x64/emit.dasc src/jit/x64/emit.dasc
index 868dddbd8..1b016d04c 100644
--- src/jit/x64/emit.dasc
+++ src/jit/x64/emit.dasc
@@ -3048,6 +3048,7 @@ void MVM_jit_emit_block_branch(MVMThreadContext *tc, MVMJitCompiler *compiler, M
         case MVM_OP_unless_s0:
             | mov ARG1, TC;
             | mov ARG2, WORK[val];
+            | xor ARG3, ARG3;
             | callp &MVM_coerce_istrue_s;
             | test RV, RV;
             if (ins->info->opcode == MVM_OP_unless_s0)