Bug 1112627: Implement shift count saturation; r=Waldo

--HG--
extra : rebase_source : c4c19f9f65f8fc88f45336e2e6f0ece708ae843f

js/src/builtin/SIMD.cpp

@@ -601,14 +601,23 @@ template<typename T>
 struct WithW {
     static inline T apply(int32_t lane, T scalar, T x) { return lane == 3 ? scalar : x; }
 };
+// For the following three operators, if the value v we're trying to shift is
+// such that v << bits can't fit in the int32 range, then we have undefined
+// behavior, according to C++11 [expr.shift]p2.
 struct ShiftLeft {
-    static inline int32_t apply(int32_t v, int32_t bits) { return v << bits; }
+    static inline int32_t apply(int32_t v, int32_t bits) {
+        return uint32_t(bits) >= 32 ? 0 : v << bits;
+    }
 };
-struct ShiftRight {
-    static inline int32_t apply(int32_t v, int32_t bits) { return v >> bits; }
+struct ShiftRightArithmetic {
+    static inline int32_t apply(int32_t v, int32_t bits) {
+        return v >> (uint32_t(bits) >= 32 ? 31 : bits);
+    }
 };
 struct ShiftRightLogical {
-    static inline int32_t apply(int32_t v, int32_t bits) { return uint32_t(v) >> (bits & 31); }
+    static inline int32_t apply(int32_t v, int32_t bits) {
+        return uint32_t(bits) >= 32 ? 0 : uint32_t(v) >> bits;
+    }
 };
 }
 

js/src/builtin/SIMD.h

@@ -157,7 +157,7 @@
   V(or, (BinaryFunc<Int32x4, Or, Int32x4>), 2)                                        \
   V(sub, (BinaryFunc<Int32x4, Sub, Int32x4>), 2)                                      \
   V(shiftLeftByScalar, (Int32x4BinaryScalar<ShiftLeft>), 2)                           \
-  V(shiftRightArithmeticByScalar, (Int32x4BinaryScalar<ShiftRight>), 2)               \
+  V(shiftRightArithmeticByScalar, (Int32x4BinaryScalar<ShiftRightArithmetic>), 2)     \
   V(shiftRightLogicalByScalar, (Int32x4BinaryScalar<ShiftRightLogical>), 2)           \
   V(store,    (Store<Int32x4, 4>), 3)                                                 \
   V(storeXYZ, (Store<Int32x4, 3>), 3)                                                 \

js/src/tests/ecma_7/SIMD/shifts.js

@@ -8,13 +8,13 @@
 var int32x4 = SIMD.int32x4;
 
 function lsh(a, b) {
-    return (a << b) | 0;
+    return (b >>> 0) >= 32 ? 0 : (a << b) | 0;
 }
 function rsh(a, b) {
-    return (a >> b) | 0;
+    return (a >> Math.min(b >>> 0, 31)) | 0;
 }
 function ursh(a, b) {
-    return (a >>> b) | 0;
+    return (b >>> 0) >= 32 ? 0 : (a >>> b) | 0;
 }
 
 function test() {
@@ -28,7 +28,7 @@ function test() {
             int32x4(INT32_MAX, INT32_MIN, INT32_MAX - 1, INT32_MIN + 1)
        ])
   {
-      for (var bits = 0; bits < 32; bits++) {
+      for (var bits = -2; bits < 36; bits++) {
           testBinaryScalarFunc(v, bits, int32x4.shiftLeftByScalar, lsh);
           testBinaryScalarFunc(v, bits, int32x4.shiftRightArithmeticByScalar, rsh);
           testBinaryScalarFunc(v, bits, int32x4.shiftRightLogicalByScalar, ursh);