[PATCH] Remove unreachable gcc_unreachable () at the end of functions

[Richard Biener via Gcc-patches]

It seems to be a style to place gcc_unreachable () after a
switch that handles all cases with every case returning.
Those are unreachable (well, yes!), so they will be elided
at CFG construction time and the middle-end will place
another __builtin_unreachable "after" them to note the
path doesn't lead to a return when the function is not declared
void.

So IMHO those explicit gcc_unreachable () serve no purpose,
if they could be replaced by a comment.  But since all cases
cover switches not handling a case or not returning will
likely cause some diagnostic to be emitted which is better
than running into an ICE only at runtime.

Bootstrapped and tested on x86_64-unknown-linux-gnu - any
comments?

Thanks,
Richard.

2021-11-24  Richard Biener  <rguent...@suse.de>

        * tree.h (reverse_storage_order_for_component_p): Remove
        spurious gcc_unreachable.
        * cfganal.c (dfs_find_deadend): Likewise.
        * fold-const-call.c (fold_const_logb): Likewise.
        (fold_const_significand): Likewise.
        * gimple-ssa-store-merging.c (lhs_valid_for_store_merging_p):
        Likewise.

gcc/c-family/
        * c-format.c (check_format_string): Remove spurious
        gcc_unreachable.
---
 gcc/c-family/c-format.c        | 2 --
 gcc/cfganal.c                  | 2 --
 gcc/fold-const-call.c          | 2 --
 gcc/gimple-ssa-store-merging.c | 2 --
 gcc/tree.h                     | 2 --
 5 files changed, 10 deletions(-)

diff --git a/gcc/c-family/c-format.c b/gcc/c-family/c-format.c
index e735e092043..617fb5ea626 100644
--- a/gcc/c-family/c-format.c
+++ b/gcc/c-family/c-format.c
@@ -296,8 +296,6 @@ check_format_string (const_tree fntype, unsigned 
HOST_WIDE_INT format_num,
       *no_add_attrs = true;
       return false;
     }
-
-  gcc_unreachable ();
 }
 
 /* Under the control of FLAGS, verify EXPR is a valid constant that
diff --git a/gcc/cfganal.c b/gcc/cfganal.c
index 0cba612738d..48598e55c01 100644
--- a/gcc/cfganal.c
+++ b/gcc/cfganal.c
@@ -752,8 +752,6 @@ dfs_find_deadend (basic_block bb)
          next = e ? e->dest : EDGE_SUCC (bb, 0)->dest;
        }
     }
-
-  gcc_unreachable ();
 }
 
 
diff --git a/gcc/fold-const-call.c b/gcc/fold-const-call.c
index d6cb9b11a31..c542e780a18 100644
--- a/gcc/fold-const-call.c
+++ b/gcc/fold-const-call.c
@@ -429,7 +429,6 @@ fold_const_logb (real_value *result, const real_value *arg,
        }
       return false;
     }
-  gcc_unreachable ();
 }
 
 /* Try to evaluate:
@@ -463,7 +462,6 @@ fold_const_significand (real_value *result, const 
real_value *arg,
        }
       return false;
     }
-  gcc_unreachable ();
 }
 
 /* Try to evaluate:
diff --git a/gcc/gimple-ssa-store-merging.c b/gcc/gimple-ssa-store-merging.c
index e7c90ba8b59..13413ca4cd6 100644
--- a/gcc/gimple-ssa-store-merging.c
+++ b/gcc/gimple-ssa-store-merging.c
@@ -4861,8 +4861,6 @@ lhs_valid_for_store_merging_p (tree lhs)
     default:
       return false;
     }
-
-  gcc_unreachable ();
 }
 
 /* Return true if the tree RHS is a constant we want to consider
diff --git a/gcc/tree.h b/gcc/tree.h
index f0e72b55abe..094501bd9b1 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -5110,8 +5110,6 @@ reverse_storage_order_for_component_p (tree t)
     default:
       return false;
     }
-
-  gcc_unreachable ();
 }
 
 /* Return true if T is a storage order barrier, i.e. a VIEW_CONVERT_EXPR
-- 
2.31.1