Fixed register allocation corner case.

test/mjsunit/compiler/regress-177883.js

Index: test/mjsunit/compiler/regress-177883.js
diff --git a/test/mjsunit/compiler/regress-177883.js b/test/mjsunit/compiler/regress-177883.js
new file mode 100644
index 0000000000000000000000000000000000000000..1586aeb4a6344ba8699f810943275a15a2eebda0
--- /dev/null
+++ b/test/mjsunit/compiler/regress-177883.js
@@ -0,0 +1,178 @@
+// Copyright 2013 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax
+
+// A regression test for a register allocation bug triggered by
+// http://n3emscripten.appspot.com/dragons_asmjs.html. Note that the test is
+// very fragile, but without a proper testing infrastructure for the register
+// allocator we can't really do much better.
+//
+// The code below is a slighty modified version of Emscripten-translated C++
+// code for the standard textbook algorithm for frustum culling of an object
+// with a given bounding box.
+//
+// The key problem for the underlying bug was a value with a long live range
+// which is used often (a context) and a lot of live ranges starting at the same
+// point. The bug was that none of the ranges were allowed to be spilled, so the
+// allocator tried to split of an empty range, making no progress at all.

[Vyacheslav Egorov (Chromium), 2013/03/11 08:43:15]

register allocator was splitting live range at its start readding the very same
range into the list of unallocated ranges and thus making no progress.

[Sven Panne, 2013/03/11 09:48:03]

Done.

+
+(function () {
+  function __ZNK4Math5plane3dotERKNS_6float4E(i1, i2) {
+    i1 = i1 | 0;
+    i2 = i2 | 0;
+    return +(+HEAPF32[i1 >> 2] * +HEAPF32[i2 >> 2] + +HEAPF32[i1 + 4 >> 2] * +HEAPF32[i2 + 4 >> 2] + +HEAPF32[i1 + 8 >> 2] * +HEAPF32[i2 + 8 >> 2] + +HEAPF32[i1 + 12 >> 2] * +HEAPF32[i2 + 12 >> 2]);

[danno, 2013/03/11 08:39:57]

nits: 80 col here and below

[Sven Panne, 2013/03/11 09:48:03]

As discussed offline, let's keep this as it is if our tools are happy with it.
Furthermore, actually splitting the lines hurts readability far more than
helping it. The Google style guide is basically useless with mangled C++
names...

+  }
+
+  function __ZNK4Math7frustum8clipmaskERKNS_5pointE(i1, i2) {
+    i1 = i1 | 0;
+    i2 = i2 | 0;
+    var i3 = 0, i4 = 0;
+    i3 = i2 | 0;
+    i2 = +__ZNK4Math5plane3dotERKNS_6float4E(i1 | 0, i3) > 0.0 & 1;
+    i4 = +__ZNK4Math5plane3dotERKNS_6float4E(i1 + 16 | 0, i3) > 0.0 ? i2 | 2 : i2;
+    i2 = +__ZNK4Math5plane3dotERKNS_6float4E(i1 + 32 | 0, i3) > 0.0 ? i4 | 4 : i4;
+    i4 = +__ZNK4Math5plane3dotERKNS_6float4E(i1 + 48 | 0, i3) > 0.0 ? i2 | 8 : i2;
+    i2 = +__ZNK4Math5plane3dotERKNS_6float4E(i1 + 64 | 0, i3) > 0.0 ? i4 | 16 : i4;
+    return (+__ZNK4Math5plane3dotERKNS_6float4E(i1 + 80 | 0, i3) > 0.0 ? i2 | 32 : i2) | 0;
+  }
+
+  function __ZNK4Math7frustum10clipstatusERKNS_4bboxE(i1, i2) {
+    i1 = i1 | 0;
+    i2 = i2 | 0;
+    var i3 = 0, i4 = 0, i5 = 0, i6 = 0, i7 = 0, i8 = 0, i9 = 0, i10 = 0, i11 = 0, i12 = 0, i13 = 0, i14 = 0, i15 = 0, i16 = 0, d17 = 0.0, d18 = 0.0, i19 = 0, i20 = 0, i21 = 0, i22 = 0;
+    i3 = STACKTOP;
+    STACKTOP = STACKTOP + 16 | 0;
+    i4 = i3 | 0;
+    i5 = i4 | 0;
+    HEAPF32[i5 >> 2] = 0.0;
+    i6 = i4 + 4 | 0;
+    HEAPF32[i6 >> 2] = 0.0;
+    i7 = i4 + 8 | 0;
+    HEAPF32[i7 >> 2] = 0.0;
+    i8 = i4 + 12 | 0;
+    HEAPF32[i8 >> 2] = 1.0;
+    i9 = i2 | 0;
+    i10 = i2 + 4 | 0;
+    i11 = i2 + 8 | 0;
+    i12 = i2 + 20 | 0;
+    i13 = i2 + 16 | 0;
+    i14 = i2 + 24 | 0;
+    i2 = 65535;
+    i15 = 0;
+    i16 = 0;
+    while (1) {
+      if ((i16 | 0) == 1) {
+        d17 = +HEAPF32[i12 >> 2];
+        d18 = +HEAPF32[i11 >> 2];
+        HEAPF32[i5 >> 2] = +HEAPF32[i9 >> 2];
+        HEAPF32[i6 >> 2] = d17;
+        HEAPF32[i7 >> 2] = d18;
+        HEAPF32[i8 >> 2] = 1.0;
+      } else if ((i16 | 0) == 4) {
+        HEAPF32[i5 >> 2] = +HEAPF32[i13 >> 2];
+        HEAPF32[i6 >> 2] = +HEAPF32[i12 >> 2];
+        HEAPF32[i7 >> 2] = +HEAPF32[i14 >> 2];
+        HEAPF32[i8 >> 2] = 1.0;
+      } else if ((i16 | 0) == 6) {
+        d18 = +HEAPF32[i10 >> 2];
+        d17 = +HEAPF32[i14 >> 2];
+        HEAPF32[i5 >> 2] = +HEAPF32[i9 >> 2];
+        HEAPF32[i6 >> 2] = d18;
+        HEAPF32[i7 >> 2] = d17;
+        HEAPF32[i8 >> 2] = 1.0;
+      } else if ((i16 | 0) == 5) {
+        d17 = +HEAPF32[i12 >> 2];
+        d18 = +HEAPF32[i14 >> 2];
+        HEAPF32[i5 >> 2] = +HEAPF32[i9 >> 2];
+        HEAPF32[i6 >> 2] = d17;
+        HEAPF32[i7 >> 2] = d18;
+        HEAPF32[i8 >> 2] = 1.0;
+      } else if ((i16 | 0) == 3) {
+        d18 = +HEAPF32[i10 >> 2];
+        d17 = +HEAPF32[i11 >> 2];
+        HEAPF32[i5 >> 2] = +HEAPF32[i13 >> 2];
+        HEAPF32[i6 >> 2] = d18;
+        HEAPF32[i7 >> 2] = d17;
+        HEAPF32[i8 >> 2] = 1.0;
+      } else if ((i16 | 0) == 0) {
+        HEAPF32[i5 >> 2] = +HEAPF32[i9 >> 2];
+        HEAPF32[i6 >> 2] = +HEAPF32[i10 >> 2];
+        HEAPF32[i7 >> 2] = +HEAPF32[i11 >> 2];
+        HEAPF32[i8 >> 2] = 1.0;
+      } else if ((i16 | 0) == 2) {
+        d17 = +HEAPF32[i12 >> 2];
+        d18 = +HEAPF32[i11 >> 2];
+        HEAPF32[i5 >> 2] = +HEAPF32[i13 >> 2];
+        HEAPF32[i6 >> 2] = d17;
+        HEAPF32[i7 >> 2] = d18;
+        HEAPF32[i8 >> 2] = 1.0;
+      } else if ((i16 | 0) == 7) {
+        d18 = +HEAPF32[i10 >> 2];
+        d17 = +HEAPF32[i14 >> 2];
+        HEAPF32[i5 >> 2] = +HEAPF32[i13 >> 2];
+        HEAPF32[i6 >> 2] = d18;
+        HEAPF32[i7 >> 2] = d17;
+        HEAPF32[i8 >> 2] = 1.0;
+      }
+      i19 = __ZNK4Math7frustum8clipmaskERKNS_5pointE(i1, i4) | 0;
+      i20 = i19 & i2;
+      i21 = i19 | i15;
+      i19 = i16 + 1 | 0;
+      if ((i19 | 0) == 8) {
+        break;
+      } else {
+        i2 = i20;
+        i15 = i21;
+        i16 = i19;
+      }
+    }
+    if ((i21 | 0) == 0) {
+      i22 = 0;
+      STACKTOP = i3;
+      return i22 | 0;
+    }
+    i22 = (i20 | 0) == 0 ? 2 : 1;
+    STACKTOP = i3;
+    return i22 | 0;
+  }
+
+  // -----------------------------------------------------------------
+
+  var STACKTOP = 0;
+  var HEAPF32 = new Float32Array(1000);
+
+  for (var i = 0; i < HEAPF32.length; i++) {
+    HEAPF32[i] = 1.0;
+  }
+
+  __ZNK4Math7frustum10clipstatusERKNS_4bboxE(0, 0);
+  __ZNK4Math7frustum10clipstatusERKNS_4bboxE(0, 0);
+  __ZNK4Math7frustum10clipstatusERKNS_4bboxE(0, 0);
+  %OptimizeFunctionOnNextCall(__ZNK4Math7frustum10clipstatusERKNS_4bboxE);
+  __ZNK4Math7frustum10clipstatusERKNS_4bboxE(0, 0);
+})();