Fix an undetected Smi overflow on ARM.

runtime/vm/assembler_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/longjump.h"
@@ skipping 666 matching lines @@
     int64_t imm = bit_cast<int64_t, double>(immd);
     LoadImmediate(TMP, imm, pp);
     fmovdr(vd, TMP);
   }
 }
 
 
 void Assembler::AddImmediate(
     Register dest, Register rn, int64_t imm, Register pp) {
   Operand op;
+  if (imm == 0) {
+    if (dest != rn) {
+      mov(dest, rn);
+    }
+    return;
+  }
   if (Operand::CanHold(imm, kXRegSizeInBits, &op) == Operand::Immediate) {
     add(dest, rn, op);
   } else if (Operand::CanHold(-imm, kXRegSizeInBits, &op) ==
              Operand::Immediate) {
     sub(dest, rn, op);
   } else {
     // TODO(zra): Try adding top 12 bits, then bottom 12 bits.
     ASSERT(rn != TMP2);
     LoadImmediate(TMP2, imm, pp);
     add(dest, rn, Operand(TMP2));
   }
 }
 
 
 void Assembler::AddImmediateSetFlags(
     Register dest, Register rn, int64_t imm, Register pp) {
   Operand op;
   if (Operand::CanHold(imm, kXRegSizeInBits, &op) == Operand::Immediate) {

[zra, 2014/05/14 19:40:55]

ditto

[regis, 2014/05/14 19:54:53]

Done.

     adds(dest, rn, op);
   } else if (Operand::CanHold(-imm, kXRegSizeInBits, &op) ==
              Operand::Immediate) {
+    ASSERT(imm != kMinInt64);  // Would cause erroneous overflow detection.
     subs(dest, rn, op);
   } else {

[zra, 2014/05/14 19:40:55]

ASSERT(imm != kMinInt64);

[regis, 2014/05/14 19:54:53]

It would not be a problem here, since we emit an adds, not a subs.

     // TODO(zra): Try adding top 12 bits, then bottom 12 bits.
     ASSERT(rn != TMP2);
     LoadImmediate(TMP2, imm, pp);
     adds(dest, rn, Operand(TMP2));
   }
 }
 
 
+void Assembler::SubImmediateSetFlags(
+    Register dest, Register rn, int64_t imm, Register pp) {
+  Operand op;
+  if (Operand::CanHold(imm, kXRegSizeInBits, &op) == Operand::Immediate) {

[zra, 2014/05/14 19:40:55]

ditto

[regis, 2014/05/14 19:54:53]

Done.

+    subs(dest, rn, op);
+  } else if (Operand::CanHold(-imm, kXRegSizeInBits, &op) ==
+             Operand::Immediate) {
+    ASSERT(imm != kMinInt64);  // Would cause erroneous overflow detection.
+    adds(dest, rn, op);
+  } else {

[zra, 2014/05/14 19:40:55]

ASSERT(imm != kMinInt64);

[regis, 2014/05/14 19:54:53]

It would not be a problem here, since we emit a subs, not an adds.

+    // TODO(zra): Try subtracting top 12 bits, then bottom 12 bits.
+    ASSERT(rn != TMP2);
+    LoadImmediate(TMP2, imm, pp);
+    subs(dest, rn, Operand(TMP2));
+  }
+}
+
+
 void Assembler::AndImmediate(
     Register rd, Register rn, int64_t imm, Register pp) {
   Operand imm_op;
   if (Operand::IsImmLogical(imm, kXRegSizeInBits, &imm_op)) {
     andi(rd, rn, imm);
   } else {
     LoadImmediate(TMP, imm, pp);
     and_(rd, rn, Operand(TMP));
   }
 }
@@ skipping 596 matching lines @@
     LoadImmediate(TMP, tags, pp);
     StoreFieldToOffset(TMP, instance_reg, Object::tags_offset(), pp);
   } else {
     b(failure);
   }
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64