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Diffstat (limited to 'gcc/tree-parloops.c')
| -rw-r--r-- | gcc/tree-parloops.c | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/gcc/tree-parloops.c b/gcc/tree-parloops.c index ec708c6..21ed17b 100644 --- a/gcc/tree-parloops.c +++ b/gcc/tree-parloops.c @@ -1801,8 +1801,39 @@ try_transform_to_exit_first_loop_alt (struct loop *loop, gcc_assert (TREE_CODE (nit) == SSA_NAME); + /* Variable nit is the loop bound as returned by canonicalize_loop_ivs, for an + iv with base 0 and step 1 that is incremented in the latch, like this: + + <bb header>: + # iv_1 = PHI <0 (preheader), iv_2 (latch)> + ... + if (iv_1 < nit) + goto <bb latch>; + else + goto <bb exit>; + + <bb latch>: + iv_2 = iv_1 + 1; + goto <bb header>; + + The range of iv_1 is [0, nit]. The latch edge is taken for + iv_1 == [0, nit - 1] and the exit edge is taken for iv_1 == nit. So the + number of latch executions is equal to nit. + + The function max_loop_iterations gives us the maximum number of latch + executions, so it gives us the maximum value of nit. */ + widest_int nit_max; + if (!max_loop_iterations (loop, &nit_max)) + return false; + + /* Check if nit + 1 overflows. */ + widest_int type_max = wi::to_widest (TYPE_MAXVAL (nit_type)); + if (!wi::lts_p (nit_max, type_max)) + return false; + gimple def = SSA_NAME_DEF_STMT (nit); + /* Try to find nit + 1, in the form of n in an assignment nit = n - 1. */ if (def && is_gimple_assign (def) && gimple_assign_rhs_code (def) == PLUS_EXPR) |