[PATCH] PR gcc/68256 Defining TARGET_USE_CONSTANT_BLOCKS_P causes go bootstrap failure on aarch64.

[vladimir dot mezentsev at oracle dot com]

From: Vladimir Mezentsev <vladimir.mezentsev@oracle.com>

Ramana Radhakrishnan made a workaround in gcc/config/aarch64/aarch64.c to resolve
bootstrap comparison failure (2015-11-10, commit bc443a71dafa2e707bae4b2fa74f83b05dea37ab).
The real bug is in gcc/varasm.c.
hash_section() returns an unstable value.
As result, two blocks are created in get_block_for_section() for one unnamed section.
A list of objects in these blocks depends on the -gtoggle option.
I removed Ramana's workaround in gcc/config/aarch64/aarch64.c and
I fixed hash_section() in gcc/varasm.c

Bootstrapped on aarch64-unknown-linux-gnu including (c,c++ and go).
Testing finished ok.

ChangeLog:
2018-02-15  Vladimir Mezentsev  <vladimir.mezentsev@oracle.com>

PR gcc/68256
* varasm.c (hash_section): Return an unchangeble hash value
* config/aarch64/aarch64.c (aarch64_use_blocks_for_constant_p):
Return !aarch64_can_use_per_function_literal_pools_p ();
---
 gcc/config/aarch64/aarch64.c | 8 +++-----
 gcc/varasm.c                 | 2 +-
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 174310c..a0a495d 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -7596,11 +7596,9 @@ aarch64_can_use_per_function_literal_pools_p (void)
 static bool
 aarch64_use_blocks_for_constant_p (machine_mode, const_rtx)
 {
-  /* Fixme:: In an ideal world this would work similar
-     to the logic in aarch64_select_rtx_section but this
-     breaks bootstrap in gcc go.  For now we workaround
-     this by returning false here.  */
-  return false;
+  /* We can't use blocks for constants when we're using a per-function
+     constant pool.  */
+  return !aarch64_can_use_per_function_literal_pools_p ();
 }
 
 /* Select appropriate section for constants depending
diff --git a/gcc/varasm.c b/gcc/varasm.c
index b045efa..5aae5b4 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -225,7 +225,7 @@ hash_section (section *sect)
 {
   if (sect->common.flags & SECTION_NAMED)
     return htab_hash_string (sect->named.name);
-  return sect->common.flags;
+  return sect->common.flags & ~SECTION_DECLARED;
 }
 
 /* Helper routines for maintaining object_block_htab.  */
-- 
1.8.3.1