Here's a small patch to expand pow(x,n) for integer n using the powi(x,n) logic in the cse_sincos pass. OK for trunk?
For the next patch, I'll plan on expanding pow(x,n) for n in {0.5, 0.25, 0.75, 1./3., 1./6.}. This logic will be added to gimple_expand_builtin_pow. Bill 2011-05-24 Bill Schmidt <wschm...@linux.vnet.ibm.com> PR tree-optimization/46728 * tree-ssa-math-opts.c (gimple_expand_builtin_pow): New. (execute_cse_sincos): Add switch case for BUILT_IN_POW. Index: gcc/tree-ssa-math-opts.c =================================================================== --- gcc/tree-ssa-math-opts.c (revision 174129) +++ gcc/tree-ssa-math-opts.c (working copy) @@ -1024,6 +1024,39 @@ gimple_expand_builtin_powi (gimple_stmt_iterator * return NULL_TREE; } +/* ARG0 and ARG1 are the two arguments to a pow builtin call in GSI + with location info LOC. If possible, create an equivalent and + less expensive sequence of statements prior to GSI, and return an + expession holding the result. */ + +static tree +gimple_expand_builtin_pow (gimple_stmt_iterator *gsi, location_t loc, + tree arg0, tree arg1) +{ + REAL_VALUE_TYPE c, cint; + HOST_WIDE_INT n; + + /* If the exponent isn't a constant, there's nothing of interest + to be done. */ + if (TREE_CODE (arg1) != REAL_CST) + return NULL_TREE; + + /* If the exponent is equivalent to an integer, expand it into + multiplies when profitable. */ + c = TREE_REAL_CST (arg1); + n = real_to_integer (&c); + real_from_integer (&cint, VOIDmode, n, n < 0 ? -1 : 0, 0); + + if (real_identical (&c, &cint) + && ((n >= -1 && n <= 2) + || (flag_unsafe_math_optimizations + && optimize_insn_for_speed_p () + && powi_cost (n) <= POWI_MAX_MULTS))) + return gimple_expand_builtin_powi (gsi, loc, arg0, n); + + return NULL_TREE; +} + /* Go through all calls to sin, cos and cexpi and call execute_cse_sincos_1 on the SSA_NAME argument of each of them. Also expand powi(x,n) into an optimal number of multiplies, when n is a constant. */ @@ -1065,6 +1098,23 @@ execute_cse_sincos (void) cfg_changed |= execute_cse_sincos_1 (arg); break; + CASE_FLT_FN (BUILT_IN_POW): + arg0 = gimple_call_arg (stmt, 0); + arg1 = gimple_call_arg (stmt, 1); + + loc = gimple_location (stmt); + result = gimple_expand_builtin_pow (&gsi, loc, arg0, arg1); + + if (result) + { + tree lhs = gimple_get_lhs (stmt); + gimple new_stmt = gimple_build_assign (lhs, result); + gimple_set_location (new_stmt, loc); + unlink_stmt_vdef (stmt); + gsi_replace (&gsi, new_stmt, true); + } + break; + CASE_FLT_FN (BUILT_IN_POWI): arg0 = gimple_call_arg (stmt, 0); arg1 = gimple_call_arg (stmt, 1);