Fix the full compiler on ARM to always generate the same code

src/arm/code-stubs-arm.cc

 // Copyright 2012 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1841 matching lines @@
   // tagged as a small integer.
   __ InvokeBuiltin(native, JUMP_FUNCTION);
 }
 
 
 // The stub expects its argument in the tos_ register and returns its result in
 // it, too: zero for false, and a non-zero value for true.
 void ToBooleanStub::Generate(MacroAssembler* masm) {
   // This stub overrides SometimesSetsUpAFrame() to return false.  That means
   // we cannot call anything that could cause a GC from this stub.
-  // This stub uses VFP3 instructions.
-  CpuFeatures::Scope scope(VFP2);
-
   Label patch;
   const Register map = r9.is(tos_) ? r7 : r9;
+  const Register temp = map;
 
   // undefined -> false.
   CheckOddball(masm, UNDEFINED, Heap::kUndefinedValueRootIndex, false);
 
   // Boolean -> its value.
   CheckOddball(masm, BOOLEAN, Heap::kFalseValueRootIndex, false);
   CheckOddball(masm, BOOLEAN, Heap::kTrueValueRootIndex, true);
 
   // 'null' -> false.
   CheckOddball(masm, NULL_TYPE, Heap::kNullValueRootIndex, false);
@@ skipping 32 matching lines @@
   __ CompareInstanceType(map, ip, FIRST_NONSTRING_TYPE);
   __ ldr(tos_, FieldMemOperand(tos_, String::kLengthOffset), lt);
   __ Ret(lt);  // the string length is OK as the return value
   }
 
   if (types_.Contains(HEAP_NUMBER)) {
     // Heap number -> false iff +0, -0, or NaN.
     Label not_heap_number;
     __ CompareRoot(map, Heap::kHeapNumberMapRootIndex);
     __ b(ne, &not_heap_number);
-    __ vldr(d1, FieldMemOperand(tos_, HeapNumber::kValueOffset));
-    __ VFPCompareAndSetFlags(d1, 0.0);
-    // "tos_" is a register, and contains a non zero value by default.
-    // Hence we only need to overwrite "tos_" with zero to return false for
-    // FP_ZERO or FP_NAN cases. Otherwise, by default it returns true.
-    __ mov(tos_, Operand(0, RelocInfo::NONE), LeaveCC, eq);  // for FP_ZERO
-    __ mov(tos_, Operand(0, RelocInfo::NONE), LeaveCC, vs);  // for FP_NAN
+
+    if (CpuFeatures::IsSupported(VFP2)) {
+      CpuFeatures::Scope scope(VFP2);
+
+      __ vldr(d1, FieldMemOperand(tos_, HeapNumber::kValueOffset));
+      __ VFPCompareAndSetFlags(d1, 0.0);
+      // "tos_" is a register, and contains a non zero value by default.
+      // Hence we only need to overwrite "tos_" with zero to return false for
+      // FP_ZERO or FP_NAN cases. Otherwise, by default it returns true.
+      __ mov(tos_, Operand(0, RelocInfo::NONE), LeaveCC, eq);  // for FP_ZERO
+      __ mov(tos_, Operand(0, RelocInfo::NONE), LeaveCC, vs);  // for FP_NAN
+    } else {
+      Label done, not_nan, not_zero;
+      __ ldr(temp, FieldMemOperand(tos_, HeapNumber::kExponentOffset));
+      // -0 maps to false:
+      __ bic(
+          temp, temp, Operand(HeapNumber::kSignMask, RelocInfo::NONE), SetCC);
+      __ b(ne, &not_zero);
+      // If exponent word is zero then the answer depends on the mantissa word.
+      __ ldr(tos_, FieldMemOperand(tos_, HeapNumber::kMantissaOffset));
+      __ jmp(&done);
+
+      // Check for NaN.
+      __ bind(&not_zero);
+      // We already zeroed the sign bit, now shift out the mantissa so we only
+      // have the exponent left.
+      __ mov(temp, Operand(temp, LSR, HeapNumber::kMantissaBitsInTopWord));
+      unsigned int shifted_exponent_mask =
+          HeapNumber::kExponentOffset >> HeapNumber::kMantissaBitsInTopWord;

[Yang, 2012/08/10 09:57:11]

kExponentOffset's unit is bytes (8 on 32-bit system), kMantissaBitsInTopWord
(20).  The result would be 0.

Don't you mean kNaNOrInfinityLowerBoundUpper32 here? I guess it would be easier
to read if we simply mask the exponent bits and compare to
kNaNOrInfinityLowerBoundUpper32.

[Erik Corry, 2012/08/10 12:24:18]

Good catch.  Changed to kExponentMask.

+      __ cmp(temp, Operand(shifted_exponent_mask, RelocInfo::NONE));
+      __ b(ne, &not_nan);  // If exponent is not 0x7ff then it can't be a NaN.
+
+      // Reload exponent word.
+      __ ldr(temp, FieldMemOperand(tos_, HeapNumber::kExponentOffset));
+      __ tst(temp, Operand(HeapNumber::kMantissaMask, RelocInfo::NONE));
+      // If mantissa is not zero then we have a NaN, so return 0.
+      __ mov(tos_, Operand(0, RelocInfo::NONE), LeaveCC, ne);
+      __ b(ne, &done);
+
+      // Load mantissa word.
+      __ ldr(temp, FieldMemOperand(tos_, HeapNumber::kMantissaOffset));
+      __ cmp(temp, Operand(0, RelocInfo::NONE));
+      // If mantissa is not zero then we have a NaN, so return 0.
+      __ mov(tos_, Operand(0, RelocInfo::NONE), LeaveCC, ne);
+      __ b(ne, &done);
+
+      __ bind(&not_nan);
+      __ mov(tos_, Operand(1, RelocInfo::NONE));
+      __ bind(&done);
+    }
     __ Ret();
     __ bind(&not_heap_number);
   }
 
   __ bind(&patch);
   GenerateTypeTransition(masm);
 }
 
 
 void ToBooleanStub::CheckOddball(MacroAssembler* masm,
@@ skipping 5635 matching lines @@
 
   __ Pop(lr, r5, r1);
   __ Ret();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM