BoundsCheck should be extended to support array_bounds_checks_elimination

src/ia32/lithium-codegen-ia32.cc

Index: src/ia32/lithium-codegen-ia32.cc
===================================================================
--- src/ia32/lithium-codegen-ia32.cc	(revision 11854)
+++ src/ia32/lithium-codegen-ia32.cc	(working copy)
@@ -3557,13 +3557,35 @@
 
 
 void LCodeGen::DoBoundsCheck(LBoundsCheck* instr) {
+  int32_t lower_offset = instr->hydrogen()->lower_offset();
+  int32_t upper_offset = instr->hydrogen()->upper_offset();
   if (instr->index()->IsConstantOperand()) {
-    __ cmp(ToOperand(instr->length()),
-           Immediate(ToInteger32(LConstantOperand::cast(instr->index()))));
+    int32_t c_index = ToInteger32(LConstantOperand::cast(instr->index()));
+    int64_t upper_range = (int64_t)c_index + (int64_t)upper_offset;
+    if (c_index < -lower_offset || upper_range > ((int64_t)1 << 32)) {
+      DeoptimizeIf(no_condition, instr->environment());
+    }
+    __ cmp(ToOperand(instr->length()), Immediate(c_index + upper_offset));
     DeoptimizeIf(below_equal, instr->environment());
   } else {
-    __ cmp(ToRegister(instr->index()), ToOperand(instr->length()));
-    DeoptimizeIf(above_equal, instr->environment());
+    ASSERT(instr->index()->IsRegister());
+    Register reg_index = ToRegister(instr->index());
+    if (lower_offset == 0 && upper_offset == 0) {
+      __ cmp(reg_index, ToOperand(instr->length()));
+      DeoptimizeIf(above_equal, instr->environment());
+    } else {
+      Register temp_length = ToRegister(instr->TempAt(0));
+      __ mov(temp_length, ToOperand(instr->length()));
+      __ cmp(reg_index, Immediate(-lower_offset));
+      DeoptimizeIf(less, instr->environment());
+      __ sub(temp_length, Immediate(upper_offset));
+      __ cmp(reg_index, temp_length);
+      if (upper_offset >= 0) {
+        DeoptimizeIf(greater_equal, instr->environment());
+      } else {
+        DeoptimizeIf(above_equal, instr->environment());
+      }
+    }
   }
 }