Allow unaligned accesses for ARMv7.

src/arm/assembler-arm.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 59 matching lines @@
 #ifdef __arm__
   // If the compiler is allowed to use VFP then we can use VFP too in our code
   // generation even when generating snapshots. ARMv7 and hardware floating
   // point support implies VFPv3, see ARM DDI 0406B, page A1-6.
 #if defined(CAN_USE_ARMV7_INSTRUCTIONS) && defined(__VFP_FP__) \
     && !defined(__SOFTFP__)
   answer |= 1u << VFP3 | 1u << ARMv7 | 1u << VFP2;
 #endif  // defined(CAN_USE_ARMV7_INSTRUCTIONS) && defined(__VFP_FP__)
         // && !defined(__SOFTFP__)
 #endif  // _arm__
+  if (answer & (1u << ARMv7)) {
+    answer |= 1u << UNALIGNED_ACCESSES;

[Michael Starzinger, 2012/10/10 11:11:19]

It seems the UNALIGNED_ACCESSES capability solely depends on the ARMv7
capability. Couldn't we just reuse the ARMv7 capability instead?

[ulan, 2012/10/10 12:13:28]

There could be non-ARMv7 processors that support this capability, but it is
difficult detect. For now, we just allow unaligned accesses for ARMv7.

We could alias UNALIGNED_ACCESSES to ARMv7, but IMO we should keep separate
names for capabilities.

+  }
 
   return answer;
 }
 
 
 void CpuFeatures::Probe() {
   unsigned standard_features = static_cast<unsigned>(
       OS::CpuFeaturesImpliedByPlatform()) | CpuFeaturesImpliedByCompiler();
   ASSERT(supported_ == 0 || supported_ == standard_features);
 #ifdef DEBUG
@@ skipping 36 matching lines @@
   }
 
   if (!IsSupported(ARMv7) && OS::ArmCpuHasFeature(ARMv7)) {
     found_by_runtime_probing_ |= 1u << ARMv7;
   }
 
   if (!IsSupported(SUDIV) && OS::ArmCpuHasFeature(SUDIV)) {
     found_by_runtime_probing_ |= 1u << SUDIV;
   }
 
+  if (!IsSupported(UNALIGNED_ACCESSES) && OS::ArmCpuHasFeature(ARMv7)) {
+    found_by_runtime_probing_ |= 1u << UNALIGNED_ACCESSES;
+  }
+
   supported_ |= found_by_runtime_probing_;
 #endif
 
   // Assert that VFP3 implies VFP2 and ARMv7.
   ASSERT(!IsSupported(VFP3) || (IsSupported(VFP2) && IsSupported(ARMv7)));
 }
 
 
 // -----------------------------------------------------------------------------
 // Implementation of RelocInfo
@@ skipping 2567 matching lines @@
 
   // Since a constant pool was just emitted, move the check offset forward by
   // the standard interval.
   next_buffer_check_ = pc_offset() + kCheckPoolInterval;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM