Re-land "Clusterfuzz identified overflow check needed in dehoisting."

src/hydrogen-instructions.cc

Index: src/hydrogen-instructions.cc
diff --git a/src/hydrogen-instructions.cc b/src/hydrogen-instructions.cc
index 8b40a249d34372d793adad1c69c6496d82e5bd52..d7278658a752babb23c3755228956ac97f92131c 100644
--- a/src/hydrogen-instructions.cc
+++ b/src/hydrogen-instructions.cc
@@ -8,6 +8,7 @@
 #include "src/factory.h"
 #include "src/hydrogen-infer-representation.h"
 #include "src/property-details-inl.h"
+#include "src/base/safe_math.h"
 
 #if V8_TARGET_ARCH_IA32
 #include "src/ia32/lithium-ia32.h"
@@ -3484,6 +3485,24 @@ void HLoadKeyed::PrintDataTo(StringStream* stream) {
 }
 
 
+bool HLoadKeyed::TryIncreaseBaseOffset(uint32_t increase_by_value) {
+  // The base offset is usually simply the size of the array header, except
+  // with dehoisting adds an addition offset due to a array index key
+  // manipulation, in which case it becomes (array header size +
+  // constant-offset-from-key * kPointerSize)
+  uint32_t base_offset = BaseOffsetField::decode(bit_field_);
+  v8::base::internal::CheckedNumeric<uint32_t> addition_result = base_offset;
+  addition_result = addition_result + increase_by_value;

[Jakob Kummerow, 2014/06/20 08:24:50]

nit: consider using += for conciseness.

[mvstanton, 2014/06/23 08:31:14]

Done.

+  if (!addition_result.IsValid() ||
+      !BaseOffsetField::is_valid(base_offset + increase_by_value)) {

[Jakob Kummerow, 2014/06/20 08:24:50]

I'd split this check in two to make it clearer what's going on:

addition_result += increase_by_value;
if (!addition_result.IsValid()) return false;
base_offset = addition_result.ValueOrDie();
if (!BaseOffsetField::is_valid(base_offset)) return false;
bit_field_ = ...update(..., base_offset);

[mvstanton, 2014/06/23 08:31:14]

Good idea, thx, I like it better too.

+    return false;
+  }
+  base_offset = addition_result.ValueOrDie();
+  bit_field_ = BaseOffsetField::update(bit_field_, base_offset);
+  return true;
+}
+
+
 bool HLoadKeyed::UsesMustHandleHole() const {
   if (IsFastPackedElementsKind(elements_kind())) {
     return false;
@@ -4062,6 +4081,19 @@ void HAllocate::PrintDataTo(StringStream* stream) {
 }
 
 
+bool HStoreKeyed::TryIncreaseBaseOffset(uint32_t increase_by_value) {
+  // The base offset is usually simply the size of the array header, except
+  // with dehoisting adds an addition offset due to a array index key
+  // manipulation, in which case it becomes (array header size +
+  // constant-offset-from-key * kPointerSize)
+  v8::base::internal::CheckedNumeric<uint32_t> addition_result = base_offset_;
+  addition_result = addition_result + increase_by_value;

[Jakob Kummerow, 2014/06/20 08:24:50]

nit: +=

[mvstanton, 2014/06/23 08:31:14]

Done.

+  if (!addition_result.IsValid()) return false;
+  base_offset_ = addition_result.ValueOrDie();
+  return true;
+}
+
+
 bool HStoreKeyed::NeedsCanonicalization() {
   // If value is an integer or smi or comes from the result of a keyed load or
   // constant then it is either be a non-hole value or in the case of a constant