Use a primop for getting the fields of the AP_STACK rather than an FFI call

This means we can avoid some StablePtrs, and also catch cases where
the AP_STACK has been evaluated (this can happen with :history, see
the hist001 test).

2 files changed, 10 insertions, 24 deletions

diff --git a/rts/Interpreter.c b/rts/Interpreter.c
index c40d894613..fbbda9d14f 100644
--- a/rts/Interpreter.c
+++ b/rts/Interpreter.c
@@ -1375,25 +1375,6 @@ run_BCO:
     barf("interpretBCO: fell off end of the interpreter");
 }
 
-/* temporary code for peeking inside a AP_STACK and pulling out values
-   based on their stack offset - used in the debugger for inspecting
-   the local values of a breakpoint
-*/
-HsStablePtr rts_getApStackVal (HsStablePtr, int);
-HsStablePtr rts_getApStackVal (HsStablePtr apStackSptr, int offset)
-{
-   HsStablePtr resultSptr;
-   StgAP_STACK *apStack;
-   StgClosure **payload;
-   StgClosure *val;
-
-   apStack = (StgAP_STACK *) deRefStablePtr (apStackSptr);
-   payload = apStack->payload;
-   val = (StgClosure *) payload[offset+2];
-   resultSptr = getStablePtr ((P_)val); 
-   return resultSptr;
-}
-
 /* set the single step flag for the debugger to True -
    it gets set back to false in the interpreter everytime
    we hit a breakpoint
diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index bb9faddef5..cd34846925 100644
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -2165,13 +2165,18 @@ noDuplicatezh_fast
 
 getApStackValzh_fast
 {
-   W_ ap_stack, offset, val;
+   W_ ap_stack, offset, val, ok;
 
-   /* args: R1 = tso, R2 = offset */
+   /* args: R1 = AP_STACK, R2 = offset */
    ap_stack = R1;
    offset   = R2;
 
-   val = StgClosure_payload(ap_stack,offset); 
-
-   RET_P(val);
+   if (%INFO_PTR(ap_stack) == stg_AP_STACK_info) {
+        ok = 1;
+        val = StgAP_STACK_payload(ap_stack,offset); 
+   } else {
+        ok = 0;
+        val = R1;
+   }
+   RET_NP(ok,val);
 }