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JIT: Loop hoisting is overly-conservative with helper calls #6553
Description
Loop hoisting has code to avoid illegally re-ordering side-effects, which includes a check for calls that is overly-general. The check looks at the GTF_CALL flag, which (A) will be set for the entire expression containing a call as a sub-expression (which is unnecessary because this code is walking the whole tree), and (B) doesn't distinguish non-side-effecting helper calls, like we do in value-numbering and in the code just above that identifies hoistable calls. This blocks hoisting of the m_arr accesses (because of the GetStaticBase helper call that precedes them) in the following code, even with a fix for #6552 in place:
using System;
using System.Diagnostics;
class ArrayPerf
{
private static int[] m_arr;
private const int MAX_ARRAY_SIZE = 4096;
private static readonly int DIM_1 = MAX_ARRAY_SIZE;
static void Main(string[] args)
{
long iterations = Int64.Parse(args[0]);
int value;
m_arr = new int[DIM_1];
for (int i = 0; i < DIM_1; i++)
m_arr[i] = i;
for (int j = 0; j < DIM_1; j++)
value = m_arr[j];
//var sw = Stopwatch.StartNew();
for (long i = 0; i < iterations; i++)
{
for (int j = 0; j < DIM_1; j++)
{
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
value = m_arr[j];
}
}
//sw.Stop();
//Console.WriteLine(sw.ElapsedMilliseconds);
}
}
Activity
Recognize mod-free helper calls in loop hoisting
Recognize mod-free helper calls in loop hoisting
Recognize mod-free helper calls in loop hoisting
Recognize mod-free helper calls in loop hoisting
Recognize mod-free helper calls in loop hoisting
Recognize mod-free helper calls in loop hoisting