The attached patch optimizes
__result_f = __builtin_powif (-1.0e+0, k);
to
powi_cond_4 = k_1(D) & 1;
powi_5 = powi_cond_4 ? -1.0e+0 : 1.0e+0;
I did an all-language (all,ada,go,objc++) bootstrap and regtest on
x86-64-gnu-linux.
OK for the trunk?
Additionally, I would like to thank Thomas, who tried several approaches
(e.g. fold_builtin_powi - which turned out to failed when called during
optimization time, as regimplifing had problems with the COND_EXPR) and
paved the way for this patch. And to Jakub, who gave helpful hints.
Note: Other replacements are also possible, e.g. "1.0 - (float) ((k & 1)
<< 1)". However, the condition above turned out to be fasted as Jakub
expected and Thomas has tested (see PR).
Tobias
2013-05-30 Tobias Brusnu <bur...@net-b.de>
PR middle-end/57073
* tree-ssa-math-opts.c (execute_cse_sincos): Optimize
powi (-1.0, k) to (k & 1) ? -1.0 : 1.0.
2013-05-30 Tobias Brusnu <bur...@net-b.de>
PR middle-end/57073
* gfortran.dg/power_6.f90: New.
diff --git a/gcc/testsuite/gfortran.dg/power_6.f90 b/gcc/testsuite/gfortran.dg/power_6.f90
new file mode 100644
index 0000000..65d1bd0
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/power_6.f90
@@ -0,0 +1,15 @@
+! { dg-do compile }
+! { dg-options "-O1 -fdump-tree-optimized" }
+!
+! PR middle-end/57073
+! See also PR 57073
+!
+real function f(k)
+ integer, value :: k
+ f = (-1.0)**k
+end
+
+! { dg-final { scan-tree-dump-not "__builtin_powif" "optimized" } }
+! { dg-final { scan-tree-dump "powi_cond_\[0-9\] = k_\[0-9\]\\(D\\) & 1;" "optimized" } }
+! { dg-final { scan-tree-dump "powi_\[0-9\] = powi_cond_\[0-9\] \\? -1.0e\\+0 : 1.0e\\+0;" "optimized" } }
+! { dg-final { cleanup-tree-dump "optimized" } }
diff --git a/gcc/tree-ssa-math-opts.c b/gcc/tree-ssa-math-opts.c
index a94172d..a15c404 100644
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -1445,12 +1445,43 @@ execute_cse_sincos (void)
CASE_FLT_FN (BUILT_IN_POWI):
arg0 = gimple_call_arg (stmt, 0);
arg1 = gimple_call_arg (stmt, 1);
- if (!host_integerp (arg1, 0))
- break;
-
- n = TREE_INT_CST_LOW (arg1);
loc = gimple_location (stmt);
- result = gimple_expand_builtin_powi (&gsi, loc, arg0, n);
+
+ if (real_minus_onep (arg0)
+ && TREE_CODE (TREE_TYPE (arg1)) == INTEGER_TYPE
+ && !host_integerp (arg1,0))
+ {
+ tree t0, t1, cond, one, minus_one;
+ gimple stmt;
+
+ t0 = TREE_TYPE (arg0);
+ t1 = TREE_TYPE (arg1);
+ one = build_real (t0, dconst1);
+ minus_one = build_real (t0, dconstm1);
+
+ cond = make_temp_ssa_name (t1, NULL, "powi_cond");
+ stmt = gimple_build_assign_with_ops (BIT_AND_EXPR, cond,
+ arg1,
+ build_int_cst (t1,
+ 1));
+ gimple_set_location (stmt, loc);
+ gsi_insert_before (&gsi, stmt, GSI_SAME_STMT);
+
+ result = make_temp_ssa_name (t0, NULL, "powi");
+ stmt = gimple_build_assign_with_ops (COND_EXPR, result,
+ cond,
+ minus_one, one);
+ gimple_set_location (stmt, loc);
+ gsi_insert_before (&gsi, stmt, GSI_SAME_STMT);
+ }
+ else
+ {
+ if (!host_integerp (arg1, 0))
+ break;
+
+ n = TREE_INT_CST_LOW (arg1);
+ result = gimple_expand_builtin_powi (&gsi, loc, arg0, n);
+ }
if (result)
{
