Detecting range check elimination with PrintAssembly

[Manohar Jonnalagedda]

Hello,

following this reference on Range Check Elimination done by the Hotspot
compiler [1], I was keen in knowing how I can detect whether range checks
are taking place in loops by inspecting output using the PrintAssembly
flag; with the old PrintOptoAssembly flag, I have seen output such as the
following, which I assume to be range checks :

B11: #  B73 B12 <- B10  Freq: 1.21365
139     movq    RAX, [rsp + #24]  # spill
13e     movl    RSI, [RAX + #12 (8-bit)]  # range
141     NullCheck RAX

What is the equivalent with the new PrintAssembly flag (using hsdis)?

Moreover, as stated on the wiki page [1], loops are optimized if the stride
is a compile-time constant. I performed a few tests on a kmeans program,
with 3 nested loops, having the following (high-level) structure:

===
void method1(){
//loop 1
for(int i = 0; i< rows1; i++){
 //...
  for(int j = 0; j< rows2; j++){
  //...
   for(int k = 0; j < cols; k++){ array[j * cols + k] = //...}
  }
}
}

void method2(){
//loop 2
for(int i =0; i < rows1; i++){
  for(int j=0 ; i< rows2; j++){
    for(int k=0 ; k< cols; k++){
      array[i*cols+k] = //...
    }
  }
}
}

void main(){

 do{
   method1(); method2();
 }while(!converged)

}
====

In the first test, cols is an int whose value is determined at runtime (by
reading a file), in the second test, it is given as a compile-time
constant(3). In the second test, there is a **significant** speed-up
(around 40%). However, when studying the diff of the output of
PrintOptoAssembly for both method1 and method2, there is no difference
(apart from slight value changes in frequency). Would you have any hints as
to where I could look for differences?

Thanks a lot,
Manohar

[1] https://wikis.oracle.com/display/HotSpotInternals/RangeCheckElimination
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