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

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index e3a67606765dabd97d9e5c3c40e21032ed8f3be5..166c46f1dfec2cffa4db8f0fd8cd9c23b763c3aa 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -123,10 +123,73 @@ class MachineOperatorBuilder final : public ZoneObject {
   };
   typedef base::Flags<Flag, unsigned> Flags;
 
+  struct UnalignedAccessConfig {

[titzer, 2016/05/06 16:06:47]

Can we call this simply AlignmentRequirements?

[ivica.bogosavljevic, 2016/05/10 08:32:22]

Acknowledged.

+   public:
+    explicit UnalignedAccessConfig(bool fullUnalignedAccessSupport,
+                                   bool noUnalignedAccessSupport)
+        : fullUnalignedAccessSupport_(fullUnalignedAccessSupport),
+          noUnalignedAccessSupport_(noUnalignedAccessSupport),
+          unalingedLoadSupportedTypes_(NULL, 0),
+          unalingedStoreSupportedTypes_(NULL, 0) {
+      DCHECK(fullUnalignedAccessSupport != noUnalignedAccessSupport);
+    }
+    explicit UnalignedAccessConfig(
+        Vector<MachineType> unalingedLoadSupportedTypes,
+        Vector<MachineType> unalignedStoreSupportedTypes)
+        : fullUnalignedAccessSupport_(false),
+          noUnalignedAccessSupport_(false),
+          unalingedLoadSupportedTypes_(unalingedLoadSupportedTypes),
+          unalingedStoreSupportedTypes_(unalignedStoreSupportedTypes) {}
+
+    bool IsUnalignedLoadSupported(const MachineType& machineType,
+                                  uint8_t alignment) const {
+      return IsUnalingedSupported(unalingedLoadSupportedTypes_, machineType,
+                                  alignment);
+    }
+
+    bool IsUnalignedStoreSupported(const MachineType& machineType,
+                                   uint8_t alignment) const {
+      return IsUnalingedSupported(unalingedStoreSupportedTypes_, machineType,
+                                  alignment);
+    }
+
+    static UnalignedAccessConfig FullUnalignedAccessSupport() {
+      return UnalignedAccessConfig(true, false);
+    }
+    static UnalignedAccessConfig NoUnalignedAccessSupport() {
+      return UnalignedAccessConfig(false, true);
+    }
+
+   private:
+    bool IsUnalingedSupported(const Vector<MachineType>& supported,
+                              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_;
+    const bool noUnalignedAccessSupport_;
+    const Vector<MachineType> unalingedLoadSupportedTypes_;
+    const Vector<MachineType> unalingedStoreSupportedTypes_;
+  };
+
   explicit MachineOperatorBuilder(
       Zone* zone,
       MachineRepresentation word = MachineType::PointerRepresentation(),
-      Flags supportedOperators = kNoFlags);
+      Flags supportedOperators = kNoFlags,
+      UnalignedAccessConfig unalignedAccessConfig =
+          UnalignedAccessConfig::NoUnalignedAccessSupport());
 
   const Operator* Word32And();
   const Operator* Word32Or();
@@ -511,6 +574,18 @@ class MachineOperatorBuilder final : public ZoneObject {
   bool Is64() const { return word() == MachineRepresentation::kWord64; }
   MachineRepresentation word() const { return word_; }
 
+  bool UnalignedLoadSupported(const MachineType& machineType,
+                              uint8_t alignment) {
+    return unalignedAccessConfig_.IsUnalignedLoadSupported(machineType,
+                                                           alignment);
+  }
+
+  bool UnalignedStoreSupported(const MachineType& machineType,
+                               uint8_t alignment) {
+    return unalignedAccessConfig_.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) \
@@ -545,6 +620,7 @@ class MachineOperatorBuilder final : public ZoneObject {
   MachineOperatorGlobalCache const& cache_;
   MachineRepresentation const word_;
   Flags const flags_;
+  UnalignedAccessConfig const unalignedAccessConfig_;
 
   DISALLOW_COPY_AND_ASSIGN(MachineOperatorBuilder);
 };