https://gcc.gnu.org/g:4be7d2d340a013d01a47c43d2feb6826d1b67af0
commit r15-4267-g4be7d2d340a013d01a47c43d2feb6826d1b67af0
Author: Jennifer Schmitz <jschm...@nvidia.com>
Date: Wed Sep 25 03:21:22 2024 -0700
match.pd: Fold logarithmic identities.
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/
PR tree-optimization/116826
PR tree-optimization/86710
* 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/
PR tree-optimization/116826
PR tree-optimization/86710
* gcc.dg/tree-ssa/log_ident.c: New test.
Diff:
---
gcc/match.pd | 25 ++++++++++++++
gcc/testsuite/gcc.dg/tree-ssa/log_ident.c | 56 +++++++++++++++++++++++++++++++
2 files changed, 81 insertions(+)
diff --git a/gcc/match.pd b/gcc/match.pd
index 5ed1ea033053..78084bb38582 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -8182,6 +8182,31 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(rdiv @0 (exps:s @1))
(mult @0 (exps (negate @1)))))
+ (if (! HONOR_SIGN_DEPENDENT_ROUNDING (type)
+ && ! HONOR_NANS (type) && ! HONOR_INFINITIES (type)
+ && ! flag_trapping_math
+ && ! flag_errno_math)
+ (for logs (LOG LOG2 LOG10)
+ /* Simplify logN(1.0/a) into -logN(a). */
+ (simplify
+ (logs (rdiv:s real_onep@0 @1))
+ (negate (logs @1)))
+
+ /* Simplify logN(C/a) into logN(C)-logN(a). */
+ (simplify
+ (logs (rdiv:s REAL_CST@0 @1))
+ (minus (logs! @0) (logs @1)))
+
+ /* Simplify logN(a)+logN(b) into logN(a*b). */
+ (simplify
+ (plus (logs:s @0) (logs:s @1))
+ (logs (mult @0 @1)))
+
+ /* Simplify logN(a)-logN(b) into logN(a/b). */
+ (simplify
+ (minus (logs:s @0) (logs:s @1))
+ (logs (rdiv @0 @1)))))
+
(for logs (LOG LOG2 LOG10 LOG10)
exps (EXP EXP2 EXP10 POW10)
/* logN(expN(x)) -> x. */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/log_ident.c
b/gcc/testsuite/gcc.dg/tree-ssa/log_ident.c
new file mode 100644
index 000000000000..80528beb7238
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/log_ident.c
@@ -0,0 +1,56 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ffast-math" } */
+/* { dg-require-effective-target c99_runtime } */
+
+extern void link_error(void);
+
+#define T(TYPE, C_TY, FNAME) \
+ void f_##FNAME##_1 (TYPE a) \
+ { \
+ TYPE t1 = 1.0##C_TY / a; \
+ TYPE t2 = __builtin_##FNAME (t1); \
+ TYPE t3 = __builtin_##FNAME (a); \
+ TYPE t4 = -t3; \
+ if (t2 != t4) \
+ link_error (); \
+ } \
+ void f_##FNAME##_2 (TYPE a) \
+ { \
+ TYPE t1 = 2.0##C_TY / a; \
+ TYPE t2 = __builtin_##FNAME (t1); \
+ TYPE t3 = __builtin_##FNAME (2.0); \
+ TYPE t4 = __builtin_##FNAME (a); \
+ TYPE t5 = t3 - t4; \
+ if (t2 != t5) \
+ link_error (); \
+ } \
+ void f_##FNAME##_3 (TYPE a, TYPE b) \
+ { \
+ TYPE t1 = __builtin_##FNAME (a); \
+ TYPE t2 = __builtin_##FNAME (b); \
+ TYPE t3 = t1 + t2; \
+ TYPE t4 = a * b; \
+ TYPE t5 = __builtin_##FNAME (t4); \
+ if (t3 != t5) \
+ link_error (); \
+ } \
+ void f_##FNAME##_4 (TYPE a, TYPE b) \
+ { \
+ TYPE t1 = __builtin_##FNAME (a); \
+ TYPE t2 = __builtin_##FNAME (b); \
+ TYPE t3 = t1 - t2; \
+ TYPE t4 = a / b; \
+ TYPE t5 = __builtin_##FNAME (t4); \
+ if (t3 != t5) \
+ link_error (); \
+ }
+
+#define TEST_LOGS(TYPE, C_TY, F_TY) \
+ T (TYPE, C_TY, log##F_TY) \
+ T (TYPE, C_TY, log2##F_TY) \
+ T (TYPE, C_TY, log10##F_TY)
+
+
+TEST_LOGS (double, , )
+TEST_LOGS (float, f, f)
+TEST_LOGS (long double, L, l)
