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<p>)Quick response, may be off base as I'm taking a guess based on a
quick read through.)</p>
<p>IRCE - like many llvm passes - assumes IR has been canonicalized
by other passes. If you run your IR through -O3 and then IRCE, do
you get what you expect?</p>
<p>Philip<br>
</p>
<div class="moz-cite-prefix">On 2/4/21 12:43 AM, Jie He via llvm-dev
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CABSkmVG-mR_jQ3Va3sFQvr7GXLAH+1UHCviQG3OTUg5bweQddg@mail.gmail.com">
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<pre class="gmail-bz_comment_text" id="gmail-comment_text_0" style="white-space:pre-wrap;width:50em;color:rgb(0,0,0)">Hi</pre>
<pre class="gmail-bz_comment_text" id="gmail-comment_text_0" style="white-space:pre-wrap;width:50em;color:rgb(0,0,0)">Recently, I tried to use llvm to optimize my code generated by a managed VM. this VM will instrument many range check codes before memory access operations.
I found the optimization IRCE wouldn't work when the range check with the predicate "uge". I wrote the following c/c++ code to simulate my code, where len is the max buf length:
void testIRCE(unsigned int * buf, unsigned int len, unsigned int iteration_count) {
if (iteration_count > 0) {
unsigned int i = 0;
do {
if (i >= len) { // range check
printf("overflow\n");
return;
}
buf[i] = i;
i ++;
} while (i < iteration_count);
}
}
the above code wouldn't be optimised as expected into 2 loops (iteration range splitting). I checked the llvm code, found in the function InductiveRangeCheck::parseRangeCheckICmp(), it wouldn't deal with uge cases, I'm not sure if it is intentional.
but I tried to modify the llvm IR code by replacing the uge to ult, and interchanging the operands of next branch instruction. the optimization IRCE works as expected.
my test command is below:
first, get a clean llvm IR file.
./clang++ -O3 -Xclang -disable-llvm-passes ~/testRCE.cpp -emit-llvm -S -o ~/testRCE.TBBA.ll
second, optimize it with other loop optimization.
./opt -gvn -simplifycfg -loop-simplify -loop-predication -licm -dce -mem2reg -dce -jump-threading -lcssa -simplifycfg -loop-simplify -dce -stats -debug-pass=Executions ~/testRCE.TBBA.ll -S -o ~/testRCE.mem2reg.ll
finally, take IRCE. </pre>
<span style="color:rgb(0,0,0);white-space:pre-wrap">./opt -irce-skip-profitability-checks -irce -dce -S ~/testRCE.mem2reg.ll -o ~/testRCE.irce.ll</span>--
<br>
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data-smartmail="gmail_signature"><br>
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data-smartmail="gmail_signature"><br>
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<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">Best Regards<br>
He Jie 何杰</div>
</div>
<br>
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