Fixed flooring division by -1 on ARM.

src/arm64/lithium-codegen-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
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@@ skipping 3833 matching lines @@
   // If the divisor is positive, things are easy: There can be no deopts and we
   // can simply do an arithmetic right shift.
   if (divisor == 1) return;
   int32_t shift = WhichPowerOf2Abs(divisor);
   if (divisor > 1) {
     __ Mov(result, Operand(dividend, ASR, shift));
     return;
   }
 
   // If the divisor is negative, we have to negate and handle edge cases.
-  Label not_kmin_int, done;
   __ Negs(result, dividend);
   if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
     DeoptimizeIf(eq, instr->environment());
   }
-  if (instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
-    // Note that we could emit branch-free code, but that would need one more
-    // register.
-    if (divisor == -1) {
-      DeoptimizeIf(vs, instr->environment());
-    } else {
-      __ B(vc, &not_kmin_int);
-      __ Mov(result, kMinInt / divisor);
-      __ B(&done);
-    }
+
+  // If the negation could not overflow, simply shifting is OK.
+  if (!instr->hydrogen()->CheckFlag(HValue::kLeftCanBeMinInt)) {
+    __ Mov(result, Operand(dividend, ASR, shift));
+    return;
   }
+
+  // Dividing by -1 is basically negation, unless we overflow.
+  if (divisor == -1) {
+    DeoptimizeIf(vs, instr->environment());
+    return;
+  }
+
+  // Using a conditional data processing instruction would need 1 more register.
+  Label not_kmin_int, done;
+  __ B(vc, &not_kmin_int);
+  __ Mov(result, kMinInt / divisor);
+  __ B(&done);
   __ bind(&not_kmin_int);
   __ Mov(result, Operand(dividend, ASR, shift));
   __ bind(&done);
 }
 
 
 void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
   Register dividend = ToRegister32(instr->dividend());
   int32_t divisor = instr->divisor();
   Register result = ToRegister32(instr->result());
@@ skipping 2039 matching lines @@
   __ Ldr(result, FieldMemOperand(object, JSObject::kPropertiesOffset));
   // Index is equal to negated out of object property index plus 1.
   __ Sub(result, result, Operand::UntagSmiAndScale(index, kPointerSizeLog2));
   __ Ldr(result, FieldMemOperand(result,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ Bind(deferred->exit());
   __ Bind(&done);
 }
 
 } }  // namespace v8::internal