This patch implements 4 rules for logarithmic identities in match.pd under -funsafe-math-optimizations: 1) logN(1.0/a) -> -logN(a). This avoids the division instruction. 2) logN(C/a) -> logN(C) - logN(a), where C is a real constant. Same as 1). 3) logN(a) + logN(b) -> logN(a*b). This reduces the number of calls to log function. 4) logN(a) - logN(b) -> logN(a/b). Same as 4). Tests were added for float, double, and long double.
The patch was bootstrapped and regtested on aarch64-linux-gnu and
x86_64-linux-gnu, no regression.
Additionally, SPEC 2017 fprate was run. While the transform does not seem
to be triggered, we also see no non-noise impact on performance.
OK for mainline?
Signed-off-by: Jennifer Schmitz <jschm...@nvidia.com>
gcc/
* match.pd: Fold logN(1.0/a) -> -logN(a),
logN(C/a) -> logN(C) - logN(a), logN(a) + logN(b) -> logN(a*b),
and logN(a) - logN(b) -> logN(a/b).
gcc/testsuite/
* gcc.dg/tree-ssa/log_ident.c: New test.
0001-PR86710-PR116826-match.pd-Fold-logarithmic-identitie.patch
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