Stop rewriting ICs after a certain number of rewrites

It's a pretty crude heuristic, but it stops us from endlessly
rewriting "megamorphic" IC sites.

              pyston interp2.py                         :    6.7s baseline: 6.5 (+3.0%)
              pyston raytrace.py                        :    8.3s baseline: 7.9 (+4.3%)
              pyston nbody.py                           :   10.6s baseline: 10.3 (+3.1%)
              pyston fannkuch.py                        :    7.4s baseline: 7.4 (+0.8%)
              pyston chaos.py                           :   24.2s baseline: 24.6 (-1.5%)
              pyston spectral_norm.py                   :   22.7s baseline: 30.4 (-25.4%)
              pyston fasta.py                           :    9.0s baseline: 8.4 (+7.6%)
              pyston pidigits.py                        :    4.4s baseline: 4.3 (+1.7%)
              pyston richards.py                        :    2.7s baseline: 12.5 (-78.7%)
              pyston deltablue.py                       :    2.7s baseline: 2.6 (+0.9%)
              pyston (geomean-0b9f)                     :    7.6s baseline: 9.0 (-15.2%)

There are a number of regressions; I feel like this is something
we'll be tuning a lot.

src/asm_writing/icinfo.cpp

@@ -107,6 +107,8 @@ void ICSlotRewrite::commit(CommitHook* hook) {
     // if (VERBOSITY()) printf("Commiting to %p-%p\n", start, start + ic->slot_size);
     memcpy(slot_start, buf, ic->getSlotSize());
 
+    ic->times_rewritten++;
+
     llvm::sys::Memory::InvalidateInstructionCache(slot_start, ic->getSlotSize());
 }
 
@@ -175,8 +177,8 @@ ICInfo::ICInfo(void* start_addr, void* slowpath_rtn_addr, void* continue_addr, S
                assembler::GenericRegister return_register, TypeRecorder* type_recorder)
     : next_slot_to_try(0), stack_info(stack_info), num_slots(num_slots), slot_size(slot_size),
       calling_conv(calling_conv), live_outs(live_outs.begin(), live_outs.end()), return_register(return_register),
-      type_recorder(type_recorder), failed(false), start_addr(start_addr), slowpath_rtn_addr(slowpath_rtn_addr),
-      continue_addr(continue_addr) {
+      type_recorder(type_recorder), failed(false), times_rewritten(0), start_addr(start_addr),
+      slowpath_rtn_addr(slowpath_rtn_addr), continue_addr(continue_addr) {
     for (int i = 0; i < num_slots; i++) {
         slots.push_back(ICSlotInfo(this, i));
     }
@@ -267,6 +269,6 @@ void ICInfo::clear(ICSlotInfo* icentry) {
 }
 
 bool ICInfo::shouldAttempt() {
-    return !failed;
+    return !failed && times_rewritten < 100;
 }
 }

src/asm_writing/icinfo.h

@@ -79,6 +79,8 @@ public:
     void commit(CommitHook* hook);
     void abort();
 
+    const ICInfo* getICInfo() { return ic; }
+
     friend class ICInfo;
 };
 
@@ -99,6 +101,7 @@ private:
     const assembler::GenericRegister return_register;
     TypeRecorder* const type_recorder;
     bool failed;
+    int times_rewritten;
 
     // for ICSlotRewrite:
     ICSlotInfo* pickEntryForRewrite(const char* debug_name);

src/asm_writing/rewriter.cpp

@@ -778,9 +778,6 @@ void Rewriter::commit() {
         return;
     }
 
-    static StatCounter rewriter_commits("rewriter_commits");
-    rewriter_commits.log();
-
     // Add uses for the live_outs
     for (int i = 0; i < live_outs.size(); i++) {
         live_outs[i]->uses.push_back(actions.size());
@@ -947,6 +944,9 @@ void Rewriter::commit() {
 
     finished = true;
 
+    static StatCounter rewriter_commits("rewriter_commits");
+    rewriter_commits.log();
+
     // TODO: have to check that we have enough room to write the final jmp
     rewrite->commit(this);
 

src/codegen/patchpoints.cpp

@@ -281,7 +281,7 @@ ICSetupInfo* createGenericIC(TypeRecorder* type_recorder, bool has_return_value,
 }
 
 ICSetupInfo* createGetattrIC(TypeRecorder* type_recorder) {
-    return ICSetupInfo::initialize(true, 1, 512, ICSetupInfo::Getattr, type_recorder);
+    return ICSetupInfo::initialize(true, 2, 512, ICSetupInfo::Getattr, type_recorder);
 }
 
 ICSetupInfo* createGetitemIC(TypeRecorder* type_recorder) {