From: Jan Hubicka Date: Thu, 16 Sep 2004 00:01:41 +0000 (+0200) Subject: predict.c (expr_expected_value, [...]): New function. X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=42f97fd2c234f561c35a3ec046e03b7c76317079;p=gcc.git predict.c (expr_expected_value, [...]): New function. * predict.c (expr_expected_value, strip_builtin_expect): New function. (tree_predict_by_opcode): Use it. (tree_estimate_probability): Add, for now disabled, strip_builtin_expect call. From-SVN: r87578 --- diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 39238769771..8649f2eb7c4 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,10 @@ +2004-09-13 Jan Hubicka + + * predict.c (expr_expected_value, strip_builtin_expect): New function. + (tree_predict_by_opcode): Use it. + (tree_estimate_probability): Add, for now disabled, + strip_builtin_expect call. + 2004-09-15 James E Wilson PR target/17455 diff --git a/gcc/predict.c b/gcc/predict.c index 3da32986238..af92acaf2bd 100644 --- a/gcc/predict.c +++ b/gcc/predict.c @@ -897,7 +897,139 @@ guess_outgoing_edge_probabilities (basic_block bb) combine_predictions_for_insn (BB_END (bb), bb); } +/* Return constant EXPR will likely have at execution time, NULL if unknown. + The function is used by builtin_expect branch predictor so the evidence + must come from this construct and additional possible constant folding. + + We may want to implement more involved value guess (such as value range + propagation based prediction), but such tricks shall go to new + implementation. */ + +static tree +expr_expected_value (tree expr, bitmap visited) +{ + if (TREE_CONSTANT (expr)) + return expr; + else if (TREE_CODE (expr) == SSA_NAME) + { + tree def = SSA_NAME_DEF_STMT (expr); + + /* If we were already here, break the infinite cycle. */ + if (bitmap_bit_p (visited, SSA_NAME_VERSION (expr))) + return NULL; + bitmap_set_bit (visited, SSA_NAME_VERSION (expr)); + + if (TREE_CODE (def) == PHI_NODE) + { + /* All the arguments of the PHI node must have the same constant + length. */ + int i; + tree val = NULL, new_val; + for (i = 0; i < PHI_NUM_ARGS (def); i++) + { + tree arg = PHI_ARG_DEF (def, i); + + /* If this PHI has itself as an argument, we cannot + determine the string length of this argument. However, + if we can find a expectd constant value for the other + PHI args then we can still be sure that this is + likely a constant. So be optimistic and just + continue with the next argument. */ + if (arg == PHI_RESULT (def)) + continue; + + new_val = expr_expected_value (arg, visited); + if (!new_val) + return NULL; + if (!val) + val = new_val; + else if (!operand_equal_p (val, new_val, false)) + return NULL; + } + return val; + } + if (TREE_CODE (def) != MODIFY_EXPR || TREE_OPERAND (def, 0) != expr) + return NULL; + return expr_expected_value (TREE_OPERAND (def, 1), visited); + } + else if (TREE_CODE (expr) == CALL_EXPR) + { + tree decl = get_callee_fndecl (expr); + if (!decl) + return NULL; + if (DECL_BUILT_IN (decl) && DECL_FUNCTION_CODE (decl) == BUILT_IN_EXPECT) + { + tree arglist = TREE_OPERAND (expr, 1); + tree val; + + if (arglist == NULL_TREE + || TREE_CHAIN (arglist) == NULL_TREE) + return NULL; + val = TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr, 1))); + if (TREE_CONSTANT (val)) + return val; + return TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr, 1))); + } + } + if (TREE_CODE_CLASS (TREE_CODE (expr)) == '2' + || TREE_CODE_CLASS (TREE_CODE (expr)) == '<') + { + tree op0, op1, res; + op0 = expr_expected_value (TREE_OPERAND (expr, 0), visited); + if (!op0) + return NULL; + op1 = expr_expected_value (TREE_OPERAND (expr, 1), visited); + if (!op1) + return NULL; + res = fold (build (TREE_CODE (expr), TREE_TYPE (expr), op0, op1)); + if (TREE_CONSTANT (res)) + return res; + return NULL; + } + if (TREE_CODE_CLASS (TREE_CODE (expr)) == '1') + { + tree op0, res; + op0 = expr_expected_value (TREE_OPERAND (expr, 0), visited); + if (!op0) + return NULL; + res = fold (build1 (TREE_CODE (expr), TREE_TYPE (expr), op0)); + if (TREE_CONSTANT (res)) + return res; + return NULL; + } + return NULL; +} + +/* Get rid of all builtin_expect calls we no longer need. */ +static void +strip_builtin_expect (void) +{ + basic_block bb; + FOR_EACH_BB (bb) + { + block_stmt_iterator bi; + for (bi = bsi_start (bb); !bsi_end_p (bi); bsi_next (&bi)) + { + tree stmt = bsi_stmt (bi); + tree fndecl; + tree arglist; + + if (TREE_CODE (stmt) == MODIFY_EXPR + && TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR + && (fndecl = get_callee_fndecl (TREE_OPERAND (stmt, 1))) + && DECL_BUILT_IN (fndecl) + && DECL_FUNCTION_CODE (fndecl) == BUILT_IN_EXPECT + && (arglist = TREE_OPERAND (TREE_OPERAND (stmt, 1), 1)) + && TREE_CHAIN (arglist)) + { + TREE_OPERAND (stmt, 1) = TREE_VALUE (arglist); + modify_stmt (stmt); + } + } + } +} + /* Predict using opcode of the last statement in basic block. */ static void tree_predict_by_opcode (basic_block bb) @@ -907,6 +1039,8 @@ tree_predict_by_opcode (basic_block bb) tree cond; tree op0; tree type; + tree val; + bitmap visited; if (!stmt || TREE_CODE (stmt) != COND_EXPR) return; @@ -918,6 +1052,17 @@ tree_predict_by_opcode (basic_block bb) return; op0 = TREE_OPERAND (cond, 0); type = TREE_TYPE (op0); + visited = BITMAP_XMALLOC (); + val = expr_expected_value (cond, visited); + BITMAP_XFREE (visited); + if (val) + { + if (integer_zerop (val)) + predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, NOT_TAKEN); + else + predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, TAKEN); + return; + } /* Try "pointer heuristic." A comparison ptr == 0 is predicted as false. Similarly, a comparison ptr1 == ptr2 is predicted as false. */ @@ -1072,6 +1217,8 @@ tree_estimate_probability (void) FOR_EACH_BB (bb) combine_predictions_for_bb (dump_file, bb); + if (0) /* FIXME: Enable once we are pass down the profile to RTL level. */ + strip_builtin_expect (); estimate_bb_frequencies (&loops_info); free_dominance_info (CDI_POST_DOMINATORS); remove_fake_exit_edges ();