Very small optimization of ARM compare stub.

src/arm/codegen-arm.cc

 // Copyright 2006-2009 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 29 matching lines @@
 namespace v8 {
 namespace internal {
 
 #define __ ACCESS_MASM(masm_)
 
 static void EmitIdenticalObjectComparison(MacroAssembler* masm,
                                           Label* slow,
                                           Condition cc,
                                           bool never_nan_nan);
 static void EmitSmiNonsmiComparison(MacroAssembler* masm,
-                                    Label* rhs_not_nan,
+                                    Label* lhs_not_nan,
                                     Label* slow,
                                     bool strict);
 static void EmitTwoNonNanDoubleComparison(MacroAssembler* masm, Condition cc);
 static void EmitStrictTwoHeapObjectCompare(MacroAssembler* masm);
 static void MultiplyByKnownInt(MacroAssembler* masm,
                                Register source,
                                Register destination,
                                int known_int);
 static bool IsEasyToMultiplyBy(int x);
 
@@ skipping 4710 matching lines @@
       }
     }
   }
 
   __ bind(&return_equal);
   if (cc == lt) {
     __ mov(r0, Operand(GREATER));  // Things aren't less than themselves.
   } else if (cc == gt) {
     __ mov(r0, Operand(LESS));     // Things aren't greater than themselves.
   } else {
-    __ mov(r0, Operand(0));        // Things are <=, >=, ==, === themselves.
+    __ mov(r0, Operand(EQUAL));    // Things are <=, >=, ==, === themselves.
   }
   __ mov(pc, Operand(lr));  // Return.
 
   if (cc != eq || !never_nan_nan) {
     // For less and greater we don't have to check for NaN since the result of
     // x < x is false regardless.  For the others here is some code to check
     // for NaN.
     if (cc != lt && cc != gt) {
       __ bind(&heap_number);
       // It is a heap number, so return non-equal if it's NaN and equal if it's
       // not NaN.
+
       // The representation of NaN values has all exponent bits (52..62) set,
       // and not all mantissa bits (0..51) clear.
       // Read top bits of double representation (second word of value).
       __ ldr(r2, FieldMemOperand(r0, HeapNumber::kExponentOffset));
       // Test that exponent bits are all set.
       __ and_(r3, r2, Operand(exp_mask_reg));
       __ cmp(r3, Operand(exp_mask_reg));
       __ b(ne, &return_equal);
 
       // Shift out flag and all exponent bits, retaining only mantissa.
       __ mov(r2, Operand(r2, LSL, HeapNumber::kNonMantissaBitsInTopWord));
       // Or with all low-bits of mantissa.
       __ ldr(r3, FieldMemOperand(r0, HeapNumber::kMantissaOffset));
       __ orr(r0, r3, Operand(r2), SetCC);
       // For equal we already have the right value in r0:  Return zero (equal)
-      // if all bits in mantissa are zero (it's an Infinity) and non-zero if not
-      // (it's a NaN).  For <= and >= we need to load r0 with the failing value
-      // if it's a NaN.
+      // if all bits in mantissa are zero (it's an Infinity) and non-zero if
+      // not (it's a NaN).  For <= and >= we need to load r0 with the failing
+      // value if it's a NaN.
       if (cc != eq) {
         // All-zero means Infinity means equal.
         __ mov(pc, Operand(lr), LeaveCC, eq);  // Return equal
         if (cc == le) {
           __ mov(r0, Operand(GREATER));  // NaN <= NaN should fail.
         } else {
           __ mov(r0, Operand(LESS));     // NaN >= NaN should fail.
         }
       }
       __ mov(pc, Operand(lr));  // Return.
     }
     // No fall through here.
   }
 
   __ bind(&not_identical);
 }
 
 
 // See comment at call site.
 static void EmitSmiNonsmiComparison(MacroAssembler* masm,
-                                    Label* rhs_not_nan,
+                                    Label* lhs_not_nan,
                                     Label* slow,
                                     bool strict) {
   Label lhs_is_smi;
   __ tst(r0, Operand(kSmiTagMask));
   __ b(eq, &lhs_is_smi);
 
   // Rhs is a Smi.  Check whether the non-smi is a heap number.
   __ CompareObjectType(r0, r4, r4, HEAP_NUMBER_TYPE);
   if (strict) {
     // If lhs was not a number and rhs was a Smi then strict equality cannot
@@ skipping 17 matching lines @@
     __ Call(stub1.GetCode(), RelocInfo::CODE_TARGET);
   }
 
 
   // r3 and r2 are rhs as double.
   __ ldr(r1, FieldMemOperand(r0, HeapNumber::kValueOffset + kPointerSize));
   __ ldr(r0, FieldMemOperand(r0, HeapNumber::kValueOffset));
   // We now have both loaded as doubles but we can skip the lhs nan check
   // since it's a Smi.
   __ pop(lr);
-  __ jmp(rhs_not_nan);
+  __ jmp(lhs_not_nan);
 
   __ bind(&lhs_is_smi);
   // Lhs is a Smi.  Check whether the non-smi is a heap number.
   __ CompareObjectType(r1, r4, r4, HEAP_NUMBER_TYPE);
   if (strict) {
     // If lhs was not a number and rhs was a Smi then strict equality cannot
     // succeed.  Return non-equal.
     __ mov(r0, Operand(1), LeaveCC, ne);  // Non-zero indicates not equal.
     __ mov(pc, Operand(lr), LeaveCC, ne);  // Return.
   } else {
@@ skipping 15 matching lines @@
     __ mov(r7, Operand(r0));
     ConvertToDoubleStub stub2(r1, r0, r7, r6);
     __ Call(stub2.GetCode(), RelocInfo::CODE_TARGET);
   }
 
   __ pop(lr);
   // Fall through to both_loaded_as_doubles.
 }
 
 
-void EmitNanCheck(MacroAssembler* masm, Label* rhs_not_nan, Condition cc) {
+void EmitNanCheck(MacroAssembler* masm, Label* lhs_not_nan, Condition cc) {
   bool exp_first = (HeapNumber::kExponentOffset == HeapNumber::kValueOffset);
-  Register lhs_exponent = exp_first ? r0 : r1;
-  Register rhs_exponent = exp_first ? r2 : r3;
-  Register lhs_mantissa = exp_first ? r1 : r0;
-  Register rhs_mantissa = exp_first ? r3 : r2;
+  Register rhs_exponent = exp_first ? r0 : r1;
+  Register lhs_exponent = exp_first ? r2 : r3;
+  Register rhs_mantissa = exp_first ? r1 : r0;
+  Register lhs_mantissa = exp_first ? r3 : r2;
   Label one_is_nan, neither_is_nan;
+  Label lhs_not_nan_exp_mask_is_loaded;
 
   Register exp_mask_reg = r5;
 
   __ mov(exp_mask_reg, Operand(HeapNumber::kExponentMask));
+  __ and_(r4, lhs_exponent, Operand(exp_mask_reg));
+  __ cmp(r4, Operand(exp_mask_reg));
+  __ b(ne, &lhs_not_nan_exp_mask_is_loaded);
+  __ mov(r4,
+         Operand(lhs_exponent, LSL, HeapNumber::kNonMantissaBitsInTopWord),
+         SetCC);
+  __ b(ne, &one_is_nan);
+  __ cmp(lhs_mantissa, Operand(0));
+  __ b(ne, &one_is_nan);
+
+  __ bind(lhs_not_nan);
+  __ mov(exp_mask_reg, Operand(HeapNumber::kExponentMask));
+  __ bind(&lhs_not_nan_exp_mask_is_loaded);
   __ and_(r4, rhs_exponent, Operand(exp_mask_reg));
   __ cmp(r4, Operand(exp_mask_reg));
-  __ b(ne, rhs_not_nan);
+  __ b(ne, &neither_is_nan);
   __ mov(r4,
          Operand(rhs_exponent, LSL, HeapNumber::kNonMantissaBitsInTopWord),
          SetCC);
   __ b(ne, &one_is_nan);
   __ cmp(rhs_mantissa, Operand(0));
-  __ b(ne, &one_is_nan);
-
-  __ bind(rhs_not_nan);
-  __ mov(exp_mask_reg, Operand(HeapNumber::kExponentMask));
-  __ and_(r4, lhs_exponent, Operand(exp_mask_reg));
-  __ cmp(r4, Operand(exp_mask_reg));
-  __ b(ne, &neither_is_nan);
-  __ mov(r4,
-         Operand(lhs_exponent, LSL, HeapNumber::kNonMantissaBitsInTopWord),
-         SetCC);
-  __ b(ne, &one_is_nan);
-  __ cmp(lhs_mantissa, Operand(0));
   __ b(eq, &neither_is_nan);
 
   __ bind(&one_is_nan);
   // NaN comparisons always fail.
   // Load whatever we need in r0 to make the comparison fail.
   if (cc == lt || cc == le) {
     __ mov(r0, Operand(GREATER));
   } else {
     __ mov(r0, Operand(LESS));
   }
   __ mov(pc, Operand(lr));  // Return.
 
   __ bind(&neither_is_nan);
 }
 
 
 // See comment at call site.
 static void EmitTwoNonNanDoubleComparison(MacroAssembler* masm, Condition cc) {
   bool exp_first = (HeapNumber::kExponentOffset == HeapNumber::kValueOffset);
-  Register lhs_exponent = exp_first ? r0 : r1;
-  Register rhs_exponent = exp_first ? r2 : r3;
-  Register lhs_mantissa = exp_first ? r1 : r0;
-  Register rhs_mantissa = exp_first ? r3 : r2;
+  Register rhs_exponent = exp_first ? r0 : r1;
+  Register lhs_exponent = exp_first ? r2 : r3;
+  Register rhs_mantissa = exp_first ? r1 : r0;
+  Register lhs_mantissa = exp_first ? r3 : r2;
 
   // r0, r1, r2, r3 have the two doubles.  Neither is a NaN.
   if (cc == eq) {
     // Doubles are not equal unless they have the same bit pattern.
     // Exception: 0 and -0.
-    __ cmp(lhs_mantissa, Operand(rhs_mantissa));
-    __ orr(r0, lhs_mantissa, Operand(rhs_mantissa), LeaveCC, ne);
+    __ cmp(rhs_mantissa, Operand(lhs_mantissa));
+    __ orr(r0, rhs_mantissa, Operand(lhs_mantissa), LeaveCC, ne);
     // Return non-zero if the numbers are unequal.
     __ mov(pc, Operand(lr), LeaveCC, ne);
 
-    __ sub(r0, lhs_exponent, Operand(rhs_exponent), SetCC);
+    __ sub(r0, rhs_exponent, Operand(lhs_exponent), SetCC);
     // If exponents are equal then return 0.
     __ mov(pc, Operand(lr), LeaveCC, eq);
 
     // Exponents are unequal.  The only way we can return that the numbers
     // are equal is if one is -0 and the other is 0.  We already dealt
     // with the case where both are -0 or both are 0.
     // We start by seeing if the mantissas (that are equal) or the bottom
     // 31 bits of the rhs exponent are non-zero.  If so we return not
     // equal.
-    __ orr(r4, rhs_mantissa, Operand(rhs_exponent, LSL, kSmiTagSize), SetCC);
+    __ orr(r4, lhs_mantissa, Operand(lhs_exponent, LSL, kSmiTagSize), SetCC);
     __ mov(r0, Operand(r4), LeaveCC, ne);
     __ mov(pc, Operand(lr), LeaveCC, ne);  // Return conditionally.
     // Now they are equal if and only if the lhs exponent is zero in its
     // low 31 bits.
-    __ mov(r0, Operand(lhs_exponent, LSL, kSmiTagSize));
+    __ mov(r0, Operand(rhs_exponent, LSL, kSmiTagSize));
     __ mov(pc, Operand(lr));
   } else {
     // Call a native function to do a comparison between two non-NaNs.
     // Call C routine that may not cause GC or other trouble.
     __ mov(r5, Operand(ExternalReference::compare_doubles()));
     __ Jump(r5);  // Tail call.
   }
 }
 
 
@@ skipping 34 matching lines @@
     __ tst(r2, Operand(kIsSymbolMask));
     __ b(ne, &return_not_equal);
 }
 
 
 // See comment at call site.
 static void EmitCheckForTwoHeapNumbers(MacroAssembler* masm,
                                        Label* both_loaded_as_doubles,
                                        Label* not_heap_numbers,
                                        Label* slow) {
-  __ CompareObjectType(r0, r2, r2, HEAP_NUMBER_TYPE);
+  __ CompareObjectType(r0, r3, r2, HEAP_NUMBER_TYPE);
   __ b(ne, not_heap_numbers);
-  __ CompareObjectType(r1, r3, r3, HEAP_NUMBER_TYPE);
+  __ ldr(r2, FieldMemOperand(r1, HeapObject::kMapOffset));
+  __ cmp(r2, r3);
   __ b(ne, slow);  // First was a heap number, second wasn't.  Go slow case.
 
   // Both are heap numbers.  Load them up then jump to the code we have
   // for that.
   __ ldr(r2, FieldMemOperand(r1, HeapNumber::kValueOffset));
   __ ldr(r3, FieldMemOperand(r1, HeapNumber::kValueOffset + kPointerSize));
   __ ldr(r1, FieldMemOperand(r0, HeapNumber::kValueOffset + kPointerSize));
   __ ldr(r0, FieldMemOperand(r0, HeapNumber::kValueOffset));
   __ jmp(both_loaded_as_doubles);
 }
@@ skipping 16 matching lines @@
   // so they are not equal.
   __ mov(r0, Operand(1));   // Non-zero indicates not equal.
   __ mov(pc, Operand(lr));  // Return.
 }
 
 
 // On entry r0 and r1 are the things to be compared.  On exit r0 is 0,
 // positive or negative to indicate the result of the comparison.
 void CompareStub::Generate(MacroAssembler* masm) {
   Label slow;  // Call builtin.
-  Label not_smis, both_loaded_as_doubles, rhs_not_nan;
+  Label not_smis, both_loaded_as_doubles, lhs_not_nan;
 
   // NOTICE! This code is only reached after a smi-fast-case check, so
   // it is certain that at least one operand isn't a smi.
 
   // Handle the case where the objects are identical.  Either returns the answer
   // or goes to slow.  Only falls through if the objects were not identical.
   EmitIdenticalObjectComparison(masm, &slow, cc_, never_nan_nan_);
 
   // If either is a Smi (we know that not both are), then they can only
   // be strictly equal if the other is a HeapNumber.
   ASSERT_EQ(0, kSmiTag);
   ASSERT_EQ(0, Smi::FromInt(0));
   __ and_(r2, r0, Operand(r1));
   __ tst(r2, Operand(kSmiTagMask));
   __ b(ne, &not_smis);
   // One operand is a smi.  EmitSmiNonsmiComparison generates code that can:
   // 1) Return the answer.
   // 2) Go to slow.
   // 3) Fall through to both_loaded_as_doubles.
-  // 4) Jump to rhs_not_nan.
+  // 4) Jump to lhs_not_nan.
   // In cases 3 and 4 we have found out we were dealing with a number-number
   // comparison and the numbers have been loaded into r0, r1, r2, r3 as doubles.
-  EmitSmiNonsmiComparison(masm, &rhs_not_nan, &slow, strict_);
+  EmitSmiNonsmiComparison(masm, &lhs_not_nan, &slow, strict_);
 
   __ bind(&both_loaded_as_doubles);
-  // r0, r1, r2, r3 are the double representations of the left hand side
-  // and the right hand side.
-
-  // Checks for NaN in the doubles we have loaded.  Can return the answer or
-  // fall through if neither is a NaN.  Also binds rhs_not_nan.
-  EmitNanCheck(masm, &rhs_not_nan, cc_);
+  // r0, r1, r2, r3 are the double representations of the right hand side
+  // and the left hand side.
 
   if (CpuFeatures::IsSupported(VFP3)) {
+    __ bind(&lhs_not_nan);
     CpuFeatures::Scope scope(VFP3);
+    Label no_nan;
     // ARMv7 VFP3 instructions to implement double precision comparison.
     __ vmov(d6, r0, r1);
     __ vmov(d7, r2, r3);
 
-    __ vcmp(d6, d7);
-    __ vmrs(pc);
-    __ mov(r0, Operand(0), LeaveCC, eq);
-    __ mov(r0, Operand(1), LeaveCC, lt);
-    __ mvn(r0, Operand(0), LeaveCC, gt);
+    __ vcmp(d7, d6);
+    __ vmrs(pc);  // Move vector status bits to normal status bits.
+    Label nan;
+    __ b(vs, &nan);
+    __ mov(r0, Operand(EQUAL), LeaveCC, eq);
+    __ mov(r0, Operand(LESS), LeaveCC, lt);
+    __ mov(r0, Operand(GREATER), LeaveCC, gt);
+    __ mov(pc, Operand(lr));
+
+    __ bind(&nan);
+    // If one of the sides was a NaN then the v flag is set.  Load r0 with
+    // whatever it takes to make the comparison fail, since comparisons with NaN
+    // always fail.
+    if (cc_ == lt || cc_ == le) {
+      __ mov(r0, Operand(GREATER));
+    } else {
+      __ mov(r0, Operand(LESS));
+    }
     __ mov(pc, Operand(lr));
   } else {
+    // Checks for NaN in the doubles we have loaded.  Can return the answer or
+    // fall through if neither is a NaN.  Also binds lhs_not_nan.
+    EmitNanCheck(masm, &lhs_not_nan, cc_);
     // Compares two doubles in r0, r1, r2, r3 that are not NaNs.  Returns the
     // answer.  Never falls through.
     EmitTwoNonNanDoubleComparison(masm, cc_);
   }
 
   __ bind(&not_smis);
   // At this point we know we are dealing with two different objects,
   // and neither of them is a Smi.  The objects are in r0 and r1.
   if (strict_) {
     // This returns non-equal for some object types, or falls through if it
     // was not lucky.
     EmitStrictTwoHeapObjectCompare(masm);
   }
 
   Label check_for_symbols;
   // Check for heap-number-heap-number comparison.  Can jump to slow case,
   // or load both doubles into r0, r1, r2, r3 and jump to the code that handles
   // that case.  If the inputs are not doubles then jumps to check_for_symbols.
-  // In this case r2 will contain the type of r0.
+  // In this case r2 will contain the type of r0.  Never falls through.
   EmitCheckForTwoHeapNumbers(masm,
                              &both_loaded_as_doubles,
                              &check_for_symbols,
                              &slow);
 
   __ bind(&check_for_symbols);
   // In the strict case the EmitStrictTwoHeapObjectCompare already took care of
   // symbols.
   if (cc_ == eq && !strict_) {
     // Either jumps to slow or returns the answer.  Assumes that r2 is the type
@@ skipping 1548 matching lines @@
   ASSERT((static_cast<unsigned>(cc_) >> 26) < (1 << 16));
   int nnn_value = (never_nan_nan_ ? 2 : 0);
   if (cc_ != eq) nnn_value = 0;  // Avoid duplicate stubs.
   return (static_cast<unsigned>(cc_) >> 26) | nnn_value | (strict_ ? 1 : 0);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal