[mlir][tosa] Limit right-shift to 31 bits

[rsuderman]

Summary

Right shift can occur that is a 32-bit right shift. This is undefined behavior.

[mehdi_amini]

Thanks!

mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp

static void computeMultiplierAndShiftTosaScale16(double scale,
 
   assert(shiftedM <= std::numeric_limits<int32_t>::max() &&
          "Shifted mantissa exceeds 32-bit signed output type");
 
   multiplier = static_cast<int32_t>(shiftedM);
 
   // Shifting tops out at 63 bits. Right shift to make 63 bits the max.
   if (shift > 63) {
-    // Shifting the multiplier by more than 32-bits is unnecessary.
-    multiplier = multiplier >> std::min<int32_t>(32, shift - 63);
+    // Shifting the multiplier by more than 31-bits is unnecessary.
+    multiplier = multiplier >> std::min<int32_t>(31, shift - 63);
     shift = 63;
   }
 }
 
 /// From a scale value, generates multiplier and shift values where
 /// mantissa is in [-1.0,-0.5] or [0.5, 1.0] such that
 /// multiplier = mantissa*2^shift for 32-bit scaling.
 static void computeMultiplierAndShiftTosaScale32(double scale,
static void computeMultiplierAndShiftTosaScale32(double scale,
   assert(shiftedM <= std::numeric_limits<int32_t>::max() &&
          "Shifted mantissa exceeds 32-bit signed output type");
 
   multiplier = static_cast<int32_t>(shiftedM);
 
   // Shifting tops out at 63 bits. Right shift to make 63 bits the max.
   if (shift > 63) {
     // Shifting the multiplier by more than 32-bits is unnecessary.
-    multiplier = multiplier >> std::min<int32_t>(32, shift - 63);
+    multiplier = multiplier >> std::min<int32_t>(31, shift - 63);
     shift = 63;
   }
 }
 
 /// Generates a quantized multiplier/shift from double.
 void mlir::tosa::computeMultiplierAndShift(double scale, int32_t &multiplier,
                                            int32_t &shift, int32_t scaleWidth) {