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even if the loop is using expressions that we can't compute as a closed-form.
This allows us to calculate that this function always returns 55:
int test() {
double X;
int Count = 0;
for (X = 100; X > 1; X = sqrt(X), ++Count)
/*empty*/;
return Count;
}
And allows us to compute trip counts for loops like:
int h = 1;
do h = 3 * h + 1; while (h <= 256);
(which occurs in bzip2), and for this function, which occurs after inlining
and other optimizations:
int popcount()
{
int x = 666;
int result = 0;
while (x != 0) {
result = result + (x & 0x1);
x = x >> 1;
}
return result;
}
We still cannot compute the exit values of result or h in the two loops above,
which means we cannot delete the loop, but we are getting closer. Being able to
compute a constant trip count for these two loops will allow us to unroll them
completely though.
llvm-svn: 13017
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|---|---|---|
| .. | ||
| DataStructure | ||
| IPA | ||
| AliasAnalysis.cpp | ||
| AliasAnalysisCounter.cpp | ||
| AliasAnalysisEvaluator.cpp | ||
| AliasSetTracker.cpp | ||
| BasicAliasAnalysis.cpp | ||
| CFGPrinter.cpp | ||
| Expressions.cpp | ||
| InstCount.cpp | ||
| Interval.cpp | ||
| IntervalPartition.cpp | ||
| LoadValueNumbering.cpp | ||
| LoopInfo.cpp | ||
| Makefile | ||
| PostDominators.cpp | ||
| PrintSCC.cpp | ||
| ProfileInfo.cpp | ||
| ProfileInfoLoader.cpp | ||
| ProfileInfoLoaderPass.cpp | ||
| ScalarEvolution.cpp | ||
| Trace.cpp | ||
| ValueNumbering.cpp | ||