[PATCH] HIGH part of symbol ref is invalid for constant pool

[Jiufu Guo <guojiufu@linux.ibm.com>]

The high part of the symbol address is invalid for the constant pool. In
function rs6000_cannot_force_const_mem, we already return true for
"HIGH with UNSPEC" rtx. During debug GCC, I found that
rs6000_cannot_force_const_mem is called for some other HIGH code rtx
expressions which also indicate the high part of a symbol_ref.
For example:
(high:DI (const:DI (plus:DI (symbol_ref:DI ("xx") (const_int 12 [0xc])))))
(high:DI (symbol_ref:DI ("var_1")..)))

In the below case, this kind of rtx could occur in the middle of optimizations
pass but was not dumped to a file. So, no test case is attached to this
patch.

extern const unsigned int __decPOWERS[10];
void
decSetCoeff (int *residue, const unsigned int *up)
{
 unsigned int half = (unsigned int) __decPOWERS1[3] >> 1;

 if (*up >= half)
  *residue = 7;

 return;
}

This patch updates rs6000_cannot_force_const_mem to return true for
rtx with HIGH code.


Bootstrapped and regtested on ppc64le and ppc64.
Is it ok for trunk?

BR,
Jiufu Guo


gcc/ChangeLog:

	* config/rs6000/rs6000.cc (rs6000_cannot_force_const_mem):
	Return true for HIGH code rtx.

---
 gcc/config/rs6000/rs6000.cc | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 3ff16b8ae04..c2b10669627 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -9707,8 +9707,11 @@ rs6000_init_stack_protect_guard (void)
 static bool
 rs6000_cannot_force_const_mem (machine_mode mode ATTRIBUTE_UNUSED, rtx x)
 {
-  if (GET_CODE (x) == HIGH
-      && GET_CODE (XEXP (x, 0)) == UNSPEC)
+  /* High part of a symbol ref/address can not be put into constant pool. e.g.
+     (high:DI (symbol_ref:DI ("var")..)) or
+     (high:DI (unspec:DI [(symbol_ref/u:DI ("*.LC0")..)
+     (high:DI (const:DI (plus:DI (symbol_ref:DI ("xx")) (const_int 12)))).  */
+  if (GET_CODE (x) == HIGH)
     return true;
 
   /* A TLS symbol in the TOC cannot contain a sum.  */
-- 
2.17.1