https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109088
--- Comment #13 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
Hi, Richi. This is my draft approach to enhance the finding more potential
condtional reduction.
diff --git a/gcc/tree-if-conv.cc b/gcc/tree-if-conv.cc
index a8c915913ae..c25d2038f16 100644
--- a/gcc/tree-if-conv.cc
+++ b/gcc/tree-if-conv.cc
@@ -1790,8 +1790,72 @@ is_cond_scalar_reduction (gimple *phi, gimple **reduc,
tree arg_0, tree arg_1,
std::swap (r_op1, r_op2);
std::swap (r_nop1, r_nop2);
}
- else if (r_nop1 != PHI_RESULT (header_phi))
- return false;
+ else if (r_nop1 == PHI_RESULT (header_phi))
+ ;
+ else
+ {
+ /* Analyze the statement chain of STMT so that we could teach generate
+ better if-converison code sequence. We are trying to catch this
+ following situation:
+
+ loop-header:
+ reduc_1 = PHI <..., reduc_2>
+ ...
+ if (...)
+ tmp1 = reduc_1 + rhs1;
+ tmp2 = tmp1 + rhs2;
+ tmp3 = tmp2 + rhs3;
+ ...
+ reduc_3 = tmpN-1 + rhsN-1;
+
+ reduc_2 = PHI <reduc_1, reduc_3>
+
+ and convert to
+
+ reduc_2 = PHI <0, reduc_1>
+ tmp1 = rhs1 + rhs2;
+ tmp2 = tmp1 + rhs3;
+ tmp3 = tmp2 + rhs4;
+ ...
+ tmpN-1 = tmpN-2 + rhsN;
+ ifcvt = cond_expr ? tmpN-1 : 0
+ reduc_1 = tmpN-1 +/- ifcvt; */
+ if (num_imm_uses (PHI_RESULT (header_phi)) != 2)
+ return false;
+ FOR_EACH_IMM_USE_FAST (use_p, imm_iter, PHI_RESULT (header_phi))
+ {
+ gimple *use_stmt = USE_STMT (use_p);
+ if (is_gimple_assign (use_stmt))
+ {
+ if (gimple_assign_rhs_code (use_stmt) != reduction_op)
+ return false;
+ if (TREE_CODE (gimple_assign_lhs (use_stmt)) != SSA_NAME)
+ return false;
+
+ bool visited_p = false;
+ while (!visited_p)
+ {
+ use_operand_p use;
+ if (!single_imm_use (gimple_assign_lhs (use_stmt), &use,
+ &use_stmt)
+ || gimple_bb (use_stmt) != gimple_bb (stmt)
+ || !is_gimple_assign (use_stmt)
+ || TREE_CODE (gimple_assign_lhs (use_stmt)) != SSA_NAME
+ || gimple_assign_rhs_code (use_stmt) != reduction_op)
+ return false;
+
+ if (gimple_assign_lhs (use_stmt) == gimple_assign_lhs (stmt))
+ {
+ r_op2 = r_op1;
+ r_op1 = PHI_RESULT (header_phi);
+ visited_p = true;
+ }
+ }
+ }
+ else if (use_stmt != phi)
+ return false;
+ }
+ }
My approach is doing the check as follows:
tmp1 = reduc_1 + rhs1;
tmp2 = tmp1 + rhs2;
tmp3 = tmp2 + rhs3;
...
reduc_3 = tmpN-1 + rhsN-1;
Start the iteration check from "tmp1 = reduc_1 + rhs1;" until "reduc_3 = tmpN-1
+ rhsN-1;"
Make sure each statement are PLUS_EXPR for reduction sum.
Does it look reasonable ?
It succeed on vectorization.
