Hi! While we have at the RTL level noce_try_ifelse_collapse combined with simplify_cond_clz_ctz, that optimization doesn't always trigger because e.g. on powerpc there is an define_insn to compare a reg against zero and copy that register to another one and so we end up with a different pseudo in the simplify_cond_clz_ctz test and punt.
For targets that define C?Z_DEFINED_VALUE_AT_ZERO to 2 for certain modes, we can optimize it already in phiopt though, just need to ensure that we transform the __builtin_c?z* calls into .C?Z ifns because my recent VRP changes codified that the builtin calls are always undefined at zero, while ifns honor C?Z_DEFINED_VALUE_AT_ZERO equal to 2. And, in phiopt we already have popcount handling that does pretty much the same thing, except for always using a zero value rather than the one set by C?Z_DEFINED_VALUE_AT_ZERO. So, this patch extends that function to handle not just popcount, but also clz and ctz. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2020-10-20 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/97503 * tree-ssa-phiopt.c (cond_removal_in_popcount_pattern): Rename to ... (cond_removal_in_popcount_clz_ctz_pattern): ... this. Handle not just popcount, but also clz and ctz if it has C?Z_DEFINED_VALUE_AT_ZERO 2. * gcc.dg/tree-ssa/pr97503.c: New test. --- gcc/tree-ssa-phiopt.c.jj 2020-07-28 15:39:10.075755306 +0200 +++ gcc/tree-ssa-phiopt.c 2020-10-20 17:46:16.971329154 +0200 @@ -61,8 +61,9 @@ static bool minmax_replacement (basic_bl edge, edge, gimple *, tree, tree); static bool abs_replacement (basic_block, basic_block, edge, edge, gimple *, tree, tree); -static bool cond_removal_in_popcount_pattern (basic_block, basic_block, - edge, edge, gimple *, tree, tree); +static bool cond_removal_in_popcount_clz_ctz_pattern (basic_block, basic_block, + edge, edge, gimple *, + tree, tree); static bool cond_store_replacement (basic_block, basic_block, edge, edge, hash_set<tree> *); static bool cond_if_else_store_replacement (basic_block, basic_block, basic_block); @@ -344,8 +345,9 @@ tree_ssa_phiopt_worker (bool do_store_el else if (abs_replacement (bb, bb1, e1, e2, phi, arg0, arg1)) cfgchanged = true; else if (!early_p - && cond_removal_in_popcount_pattern (bb, bb1, e1, e2, - phi, arg0, arg1)) + && cond_removal_in_popcount_clz_ctz_pattern (bb, bb1, e1, + e2, phi, arg0, + arg1)) cfgchanged = true; else if (minmax_replacement (bb, bb1, e1, e2, phi, arg0, arg1)) cfgchanged = true; @@ -1777,16 +1779,20 @@ minmax_replacement (basic_block cond_bb, <bb 4> c_12 = PHI <_9(2)> -*/ + + Similarly for __builtin_clz or __builtin_ctz if + C?Z_DEFINED_VALUE_AT_ZERO is 2, optab is present and + instead of 0 above it uses the value from that macro. */ static bool -cond_removal_in_popcount_pattern (basic_block cond_bb, basic_block middle_bb, - edge e1, edge e2, - gimple *phi, tree arg0, tree arg1) +cond_removal_in_popcount_clz_ctz_pattern (basic_block cond_bb, + basic_block middle_bb, + edge e1, edge e2, gimple *phi, + tree arg0, tree arg1) { gimple *cond; gimple_stmt_iterator gsi, gsi_from; - gimple *popcount; + gimple *call; gimple *cast = NULL; tree lhs, arg; @@ -1804,35 +1810,65 @@ cond_removal_in_popcount_pattern (basic_ gsi_next_nondebug (&gsi); if (!gsi_end_p (gsi)) { - popcount = gsi_stmt (gsi); + call = gsi_stmt (gsi); gsi_next_nondebug (&gsi); if (!gsi_end_p (gsi)) return false; } else { - popcount = cast; + call = cast; cast = NULL; } - /* Check that we have a popcount builtin. */ - if (!is_gimple_call (popcount)) + /* Check that we have a popcount/clz/ctz builtin. */ + if (!is_gimple_call (call) || gimple_call_num_args (call) != 1) return false; - combined_fn cfn = gimple_call_combined_fn (popcount); + + arg = gimple_call_arg (call, 0); + lhs = gimple_get_lhs (call); + + if (lhs == NULL_TREE) + return false; + + combined_fn cfn = gimple_call_combined_fn (call); + internal_fn ifn = IFN_LAST; + int val = 0; switch (cfn) { CASE_CFN_POPCOUNT: break; + CASE_CFN_CLZ: + if (INTEGRAL_TYPE_P (TREE_TYPE (arg))) + { + scalar_int_mode mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (arg)); + if (optab_handler (clz_optab, mode) != CODE_FOR_nothing + && CLZ_DEFINED_VALUE_AT_ZERO (mode, val) == 2) + { + ifn = IFN_CLZ; + break; + } + } + return false; + CASE_CFN_CTZ: + if (INTEGRAL_TYPE_P (TREE_TYPE (arg))) + { + scalar_int_mode mode = SCALAR_INT_TYPE_MODE (TREE_TYPE (arg)); + if (optab_handler (ctz_optab, mode) != CODE_FOR_nothing + && CTZ_DEFINED_VALUE_AT_ZERO (mode, val) == 2) + { + ifn = IFN_CTZ; + break; + } + } + return false; default: return false; } - arg = gimple_call_arg (popcount, 0); - lhs = gimple_get_lhs (popcount); - if (cast) { - /* We have a cast stmt feeding popcount builtin. */ + /* We have a cast stmt feeding popcount/clz/ctz builtin. */ /* Check that we have a cast prior to that. */ if (gimple_code (cast) != GIMPLE_ASSIGN || !CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (cast))) @@ -1845,7 +1881,7 @@ cond_removal_in_popcount_pattern (basic_ cond = last_stmt (cond_bb); - /* Cond_bb has a check for b_4 [!=|==] 0 before calling the popcount + /* Cond_bb has a check for b_4 [!=|==] 0 before calling the popcount/clz/ctz builtin. */ if (gimple_code (cond) != GIMPLE_COND || (gimple_cond_code (cond) != NE_EXPR @@ -1865,10 +1901,13 @@ cond_removal_in_popcount_pattern (basic_ } /* Check PHI arguments. */ - if (lhs != arg0 || !integer_zerop (arg1)) + if (lhs != arg0 + || TREE_CODE (arg1) != INTEGER_CST + || wi::to_wide (arg1) != val) return false; - /* And insert the popcount builtin and cast stmt before the cond_bb. */ + /* And insert the popcount/clz/ctz builtin and cast stmt before the + cond_bb. */ gsi = gsi_last_bb (cond_bb); if (cast) { @@ -1876,9 +1915,19 @@ cond_removal_in_popcount_pattern (basic_ gsi_move_before (&gsi_from, &gsi); reset_flow_sensitive_info (gimple_get_lhs (cast)); } - gsi_from = gsi_for_stmt (popcount); - gsi_move_before (&gsi_from, &gsi); - reset_flow_sensitive_info (gimple_get_lhs (popcount)); + gsi_from = gsi_for_stmt (call); + if (ifn == IFN_LAST || gimple_call_internal_p (call)) + gsi_move_before (&gsi_from, &gsi); + else + { + /* For __builtin_c[lt]z* force .C[LT]Z ifn, because only + the latter is well defined at zero. */ + call = gimple_build_call_internal (ifn, 1, gimple_call_arg (call, 0)); + gimple_call_set_lhs (call, lhs); + gsi_insert_before (&gsi, call, GSI_SAME_STMT); + gsi_remove (&gsi_from, true); + } + reset_flow_sensitive_info (lhs); /* Now update the PHI and remove unneeded bbs. */ replace_phi_edge_with_variable (cond_bb, e2, phi, lhs); --- gcc/testsuite/gcc.dg/tree-ssa/pr97503.c.jj 2020-10-20 18:14:46.862749687 +0200 +++ gcc/testsuite/gcc.dg/tree-ssa/pr97503.c 2020-10-20 18:17:13.618640295 +0200 @@ -0,0 +1,19 @@ +/* PR tree-optimization/97503 */ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ +/* { dg-additional-options "-mbmi -mlzcnt" { target i?86-*-* x86_64-*-* } } */ +/* { dg-final { scan-tree-dump-times "\.CLZ" 2 "optimized" { target { { i?86-*-* x86_64-*-* aarch64-*-* powerpc*-*-* } && lp64 } } } } */ +/* { dg-final { scan-tree-dump-not "__builtin_clz" "optimized" { target { { i?86-*-* x86_64-*-* aarch64-*-* powerpc*-*-*} && lp64 } } } } */ +/* { dg-final { scan-tree-dump-not "PHI <" "optimized" { target { { i?86-*-* x86_64-*-* aarch64-*-* powerpc*-*-*} && lp64 } } } } */ + +int +foo (int x) +{ + return x ? __builtin_clz (x) : 32; +} + +int +bar (unsigned long long x) +{ + return x ? __builtin_clzll (x) : 64; +} Jakub