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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Simplify pow(C, sitofp(X))"
href="https://bugs.llvm.org/show_bug.cgi?id=42190">42190</a>
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<th>Summary</th>
<td>Simplify pow(C, sitofp(X))
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>david.bolvansky@gmail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Pattern extracted from
<a href="https://github.com/philipl/pifs/blob/master/src/piqpr8.c#L94">https://github.com/philipl/pifs/blob/master/src/piqpr8.c#L94</a>
double foo(int id, int k) {
return pow (7., id - k);
}
So I am wondering if we could do nice speed optimization.
Current TOT of clang produces IR:
%doublevalfromint = sitofp i32 %sub to double
%result = tail call double @pow(double 7.000000e+00, double %doublevalfromint)
Some suggestions:
1, Maybe we can, under -Ofast or so, transform following IR to something like:
%result = call pow_double_with_integer_exp(double 7.000000e+00,
%doublevalfromint)?
Ideally, we could match constant integer base (7 here) and use
pow_integer_with_integer_exp.
But the problem is, I am not aware whether we have any helpers for
pow_double_with_integer_exp / pow_integer_with_integer_exp. But I think this is
quite promising.
2, Specific transformation for base 2
From:
%doubleval = sitofp i32 %sub to double
%result = tail call double @pow(double 2.000000e+00, double %doubleval)
To:
%intpow = shl i32 2, %%doubleval
%result = sitofp i32 %intpow to double
?</pre>
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