Implement UnalignedLoad and UnalignedStore in WASM using LoadByte/Shift/Or and StoreByte/Shift/And.

src/compiler/machine-operator.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_MACHINE_OPERATOR_H_
 #define V8_COMPILER_MACHINE_OPERATOR_H_
 
 #include "src/base/flags.h"
 #include "src/machine-type.h"
 
@@ skipping 105 matching lines @@
     kAllOptionalOps = kFloat32Max | kFloat32Min | kFloat64Max | kFloat64Min |
                       kFloat32RoundDown | kFloat64RoundDown | kFloat32RoundUp |
                       kFloat64RoundUp | kFloat32RoundTruncate |
                       kFloat64RoundTruncate | kFloat64RoundTiesAway |
                       kFloat32RoundTiesEven | kFloat64RoundTiesEven |
                       kWord32Ctz | kWord64Ctz | kWord32Popcnt | kWord64Popcnt |
                       kWord32ReverseBits | kWord64ReverseBits
   };
   typedef base::Flags<Flag, unsigned> Flags;
 
+  struct AlignmentRequirements {

[Benedikt Meurer, 2016/05/12 04:12:14]

Nit: class

+   public:
+    explicit AlignmentRequirements(bool fullUnalignedAccessSupport,
+                                   bool noUnalignedAccessSupport)

[Jarin, 2016/05/12 04:26:13]

Nit: Could you make the constructor private now that you have the static methods
for construction? 

+        : fullUnalignedAccessSupport_(fullUnalignedAccessSupport),
+          noUnalignedAccessSupport_(noUnalignedAccessSupport),
+          unalignedLoadSupportedTypes_(NULL, 0),
+          unalignedStoreSupportedTypes_(NULL, 0) {
+      DCHECK(fullUnalignedAccessSupport != noUnalignedAccessSupport);
+    }
+    explicit AlignmentRequirements(
+        Vector<MachineType> unalingedLoadSupportedTypes,

[Jarin, 2016/05/12 04:26:13]

Typo: unalinged -> unaligned

+        Vector<MachineType> unalignedStoreSupportedTypes)
+        : fullUnalignedAccessSupport_(false),
+          noUnalignedAccessSupport_(false),
+          unalignedLoadSupportedTypes_(unalingedLoadSupportedTypes),
+          unalignedStoreSupportedTypes_(unalignedStoreSupportedTypes) {}
+
+    bool IsUnalignedLoadSupported(const MachineType& machineType,
+                                  uint8_t alignment) const {
+      return IsUnalingedSupported(unalignedLoadSupportedTypes_, machineType,
+                                  alignment);
+    }
+
+    bool IsUnalignedStoreSupported(const MachineType& machineType,
+                                   uint8_t alignment) const {
+      return IsUnalingedSupported(unalignedStoreSupportedTypes_, machineType,
+                                  alignment);
+    }
+
+    static AlignmentRequirements FullUnalignedAccessSupport() {
+      return AlignmentRequirements(true, false);
+    }
+    static AlignmentRequirements NoUnalignedAccessSupport() {
+      return AlignmentRequirements(false, true);
+    }
+
+   private:
+    bool IsUnalingedSupported(const Vector<MachineType>& supported,

[Jarin, 2016/05/12 04:26:13]

Typo: Unalinged -> Unaligned

+                              const MachineType& machineType,
+                              uint8_t alignment) const {
+      if (fullUnalignedAccessSupport_) {
+        return true;
+      } else if (noUnalignedAccessSupport_) {
+        return false;
+      } else {
+        for (MachineType m : supported) {
+          if (m == machineType) {
+            return true;
+          }
+        }
+        return false;
+      }
+    }
+
+    const bool fullUnalignedAccessSupport_;

[Benedikt Meurer, 2016/05/12 04:12:14]

How about an enum here for this tristate logic? The two bools are very
confusing. I.e.

enum class UnalignedAccessSupport {
  kNoSupport,
  kSomeSupport,
  kFullSupport
};

+    const bool noUnalignedAccessSupport_;
+    const Vector<MachineType> unalignedLoadSupportedTypes_;
+    const Vector<MachineType> unalignedStoreSupportedTypes_;
+  };
+
   explicit MachineOperatorBuilder(
       Zone* zone,
       MachineRepresentation word = MachineType::PointerRepresentation(),
-      Flags supportedOperators = kNoFlags);
+      Flags supportedOperators = kNoFlags,
+      AlignmentRequirements alignmentConfig =
+          AlignmentRequirements::NoUnalignedAccessSupport());
 
   const Operator* Word32And();
   const Operator* Word32Or();
   const Operator* Word32Xor();
   const Operator* Word32Shl();
   const Operator* Word32Shr();
   const Operator* Word32Sar();
   const Operator* Word32Ror();
   const Operator* Word32Equal();
   const Operator* Word32Clz();
@@ skipping 364 matching lines @@
   // atomic-load [base + index]
   const Operator* AtomicLoad(LoadRepresentation rep);
   // atomic-store [base + index], value
   const Operator* AtomicStore(MachineRepresentation rep);
 
   // Target machine word-size assumed by this builder.
   bool Is32() const { return word() == MachineRepresentation::kWord32; }
   bool Is64() const { return word() == MachineRepresentation::kWord64; }
   MachineRepresentation word() const { return word_; }
 
+  bool UnalignedLoadSupported(const MachineType& machineType,
+                              uint8_t alignment) {
+    return alignmentConfig_.IsUnalignedLoadSupported(machineType, alignment);
+  }
+
+  bool UnalignedStoreSupported(const MachineType& machineType,
+                               uint8_t alignment) {
+    return alignmentConfig_.IsUnalignedStoreSupported(machineType, alignment);
+  }
+
 // Pseudo operators that translate to 32/64-bit operators depending on the
 // word-size of the target machine assumed by this builder.
 #define PSEUDO_OP_LIST(V) \
   V(Word, And)            \
   V(Word, Or)             \
   V(Word, Xor)            \
   V(Word, Shl)            \
   V(Word, Shr)            \
   V(Word, Sar)            \
   V(Word, Ror)            \
@@ skipping 14 matching lines @@
     return Is32() ? Prefix##32##Suffix() : Prefix##64##Suffix(); \
   }
   PSEUDO_OP_LIST(PSEUDO_OP)
 #undef PSEUDO_OP
 #undef PSEUDO_OP_LIST
 
  private:
   MachineOperatorGlobalCache const& cache_;
   MachineRepresentation const word_;
   Flags const flags_;
+  AlignmentRequirements const alignmentConfig_;
 
   DISALLOW_COPY_AND_ASSIGN(MachineOperatorBuilder);
 };
 
 
 DEFINE_OPERATORS_FOR_FLAGS(MachineOperatorBuilder::Flags)
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_MACHINE_OPERATOR_H_