MIPS: Fix deoptimization entry table when branch cannot reach.

This fixes failures when table has more than 8192 entries, and preserves
optimization to have 2 instructions per entry.

TEST=mozilla/regress-398085-01
BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/477623002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23131 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/deoptimizer-mips.cc

@@ -324,22 +324,59 @@ void Deoptimizer::TableEntryGenerator::GeneratePrologue() {
 
   // Create a sequence of deoptimization entries.
   // Note that registers are still live when jumping to an entry.
-  Label table_start, done;
+  Label table_start, done, done_special, trampoline_jump;
   __ bind(&table_start);
-  for (int i = 0; i < count(); i++) {
-    Label start;
-    __ bind(&start);
-    DCHECK(is_int16(i));
-    __ Branch(USE_DELAY_SLOT, &done);  // Expose delay slot.
-    __ li(at, i);  // In the delay slot.
-
-    DCHECK_EQ(table_entry_size_, masm()->SizeOfCodeGeneratedSince(&start));
-  }
+  int kMaxEntriesBranchReach = (1 << (kImm16Bits - 2))/
+     (table_entry_size_ /  Assembler::kInstrSize);
+
+  if (count() <= kMaxEntriesBranchReach) {
+    // Common case.
+    for (int i = 0; i < count(); i++) {
+      Label start;
+      __ bind(&start);
+      DCHECK(is_int16(i));
+      __ Branch(USE_DELAY_SLOT, &done);  // Expose delay slot.
+      __ li(at, i);  // In the delay slot.
+
+      DCHECK_EQ(table_entry_size_, masm()->SizeOfCodeGeneratedSince(&start));
+    }
+
+    DCHECK_EQ(masm()->SizeOfCodeGeneratedSince(&table_start),
+        count() * table_entry_size_);
+    __ bind(&done);
+    __ Push(at);
+  } else {
+    // Uncommon case, the branch cannot reach.
+    // Create mini trampoline and adjust id constants to get proper value at
+    // the end of table.
+    for (int i = kMaxEntriesBranchReach; i > 1; i--) {
+      Label start;
+      __ bind(&start);
+      DCHECK(is_int16(i));
+      __ Branch(USE_DELAY_SLOT, &trampoline_jump);  // Expose delay slot.
+      __ li(at, - i);  // In the delay slot.
+      DCHECK_EQ(table_entry_size_, masm()->SizeOfCodeGeneratedSince(&start));
+    }
+    // Entry with id == kMaxEntriesBranchReach - 1.
+    __ bind(&trampoline_jump);
+    __ Branch(USE_DELAY_SLOT, &done_special);
+    __ li(at, -1);
+
+    for (int i = kMaxEntriesBranchReach ; i < count(); i++) {
+      Label start;
+      __ bind(&start);
+      DCHECK(is_int16(i));
+      __ Branch(USE_DELAY_SLOT, &done);  // Expose delay slot.
+      __ li(at, i);  // In the delay slot.
+    }
 
-  DCHECK_EQ(masm()->SizeOfCodeGeneratedSince(&table_start),
-      count() * table_entry_size_);
-  __ bind(&done);
-  __ Push(at);
+    DCHECK_EQ(masm()->SizeOfCodeGeneratedSince(&table_start),
+        count() * table_entry_size_);
+    __ bind(&done_special);
+    __ addiu(at, at, kMaxEntriesBranchReach);
+    __ bind(&done);
+    __ Push(at);
+  }
 }