https://bugs.llvm.org/show_bug.cgi?id=42190
Bug ID: 42190
Summary: Simplify pow(C, sitofp(X))
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: david.bolvan...@gmail.com
CC: llvm-bugs@lists.llvm.org
Pattern extracted from
https://github.com/philipl/pifs/blob/master/src/piqpr8.c#L94
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
?
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