MIPS64: r6 compact branch optimization.

src/mips64/simulator-mips64.h

Index: src/mips64/simulator-mips64.h
diff --git a/src/mips64/simulator-mips64.h b/src/mips64/simulator-mips64.h
index 4c67eff6636cc4d7fa7d087166fb7d951871f7d5..9627a37fb759b62644ace8a3673b51c61d98eab3 100644
--- a/src/mips64/simulator-mips64.h
+++ b/src/mips64/simulator-mips64.h
@@ -391,6 +391,18 @@ class Simulator {
   // Used for breakpoints and traps.
   void SoftwareInterrupt(Instruction* instr);
 
+  // Compact branch guard.
+  void CheckForbiddenSlot(int64_t current_pc) {
+    Instruction* instr_aftter_compact_branch =
+        reinterpret_cast<Instruction*>(current_pc + Instruction::kInstrSize);
+    if (instr_aftter_compact_branch->IsForbiddenInBranchDelay()) {
+      V8_Fatal(__FILE__, __LINE__,

[balazs.kilvady, 2015/12/18 19:18:05]

I think we should change the function name from 'IsForbiddenInBranchDelay' to
'IsForbiddenAfterBranch' on both 32 and 64 bits. What do you think?

[ivica.bogosavljevic, 2015/12/22 10:22:40]

Agree. Maybe we should have it IsForbiddenAfterBranchCompact if we are
performing the check on BranchCompact instructions.

[balazs.kilvady, 2015/12/22 11:01:56]

We can use the same function for r6 compact branches and for pre-r6 and r6 delay
slots so the 'Compact' word should not be added.

[ivica.bogosavljevic, 2015/12/22 12:23:41]

Acknowledged.

+               "Error: Unexpected instruction 0x%08x immediately after a "
+               "compact branch instruction.",
+               *reinterpret_cast<uint32_t*>(instr_aftter_compact_branch));
+    }
+  }
+
   // Stop helper functions.
   bool IsWatchpoint(uint64_t code);
   void PrintWatchpoint(uint64_t code);