Fix error in x64 fast smi loops, change 4998.

test/mjsunit/regress/regress-r4998.js

+// Copyright 2010 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:
+//
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+//     * Redistributions in binary form must reproduce the above
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+//       contributors may be used to endorse or promote products derived
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+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Test for a broken fast-smi-loop that does not save the incremented value
+// of the loop index.  If this test fails, it loops forever, and times out.
+
+// Flags: --nofull-compiler
+
+// Calling foo() spills the virtual frame.
+function foo() {
+  return;
+}
+
+function bar() {
+  var x1 = 3;
+  var x2 = 3;
+  var x3 = 3;
+  var x4 = 3;
+  var x5 = 3;
+  var x6 = 3;
+  var x7 = 3;
+  var x8 = 3;
+  var x9 = 3;
+  var x10 = 3;
+  var x11 = 3;
+  var x12 = 3;
+  var x13 = 3;
+
+  foo();
+
+  x1 = 257;
+  x2 = 258;
+  x3 = 259;
+  x4 = 260;
+  x5 = 261;
+  x6 = 262;
+  x7 = 263;
+  x8 = 264;
+  x9 = 265;
+  x10 = 266;
+  x11 = 267;
+  x12 = 268;
+  x13 = 269;
+
+  // The loop variable x7 is initialized to 3,
+  // and then MakeMergeable is called on the virtual frame.
+  // MakeMergeable has forced the loop variable x7 to be spilled,
+  // so it is marked as synced
+  // The back edge then merges its virtual frame, which incorrectly
+  // claims that x7 is synced, and does not save the modified
+  // value.
+  for (x7 = 3; x7 < 10; ++x7) {
+    foo();
+  }
+}
+
+bar();