[PATCH v3] gdb/i387-tdep.c: Avoid warning for "-Werror=strict-overflow"

[Chen Gang <gang.chen.5i5j@gmail.com>]

gdb requires "-Werror", and I387_ST0_REGNUM (tdep) is 'variable', then
compiler can think that I387_ST0_REGNUM (tdep) may be a large number to
add a constant value, which may cause issue, so report warning.

Need fix this warning, and still keep the code clear enough for readers
(I387_NUM_REGS is much clearer than I387_XMM0_REGNUM). The related
warning under Darwin with gnu built gcc:

  gcc -g -O2   -I. -I../../binutils-gdb/gdb -I../../binutils-gdb/gdb/common -I../../binutils-gdb/gdb/config -DLOCALEDIR="\"/usr/local/share/locale\"" -DHAVE_CONFIG_H -I../../binutils-gdb/gdb/../include/opcode -I../../binutils-gdb/gdb/../opcodes/..  -I../../binutils-gdb/gdb/../readline/.. -I../bfd -I../../binutils-gdb/gdb/../bfd -I../../binutils-gdb/gdb/../include -I../libdecnumber -I../../binutils-gdb/gdb/../libdecnumber -I../../binutils-gdb/gdb/gnulib/import -Ibuild-gnulib/import   -DTUI=1 -D_THREAD_SAFE -I/usr/local/Cellar/guile/2.0.11/include/guile/2.0 -I/usr/local/Cellar/gmp/6.0.0a/include -I/usr/local/Cellar/readline/6.3.5/include -I/usr/local/Cellar/bdw-gc/7.2e/include -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -Wall -Wdeclaration-after-statement -Wpointer-arith -Wpointer-sign -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wmissing-protot
 ypes -Wdeclaration-after-statement -Wempty-body -Wmissing-parameter-type -Wold-style-declaration -Wold-style-definition -Wformat-nonliteral -Werror -c -o i387-tdep.o -MT i387-tdep.o -MMD -MP -MF .deps/i387-tdep.Tpo ../../binutils-gdb/gdb/i387-tdep.c
  ../../binutils-gdb/gdb/i387-tdep.c: In function 'i387_supply_fsave':
  ../../binutils-gdb/gdb/i387-tdep.c:447:1: error: assuming signed overflow does not occur when assuming that (X + c) >= X is always true [-Werror=strict-overflow]
   i387_supply_fsave (struct regcache *regcache, int regnum, const void *fsave)
   ^
  ../../binutils-gdb/gdb/i387-tdep.c: In function 'i387_collect_fsave':
  ../../binutils-gdb/gdb/i387-tdep.c:502:1: error: assuming signed overflow does not occur when assuming that (X + c) >= X is always true [-Werror=strict-overflow]
   i387_collect_fsave (const struct regcache *regcache, int regnum, void *fsave)
   ^
  cc1: all warnings being treated as errors

Also give related comment for it, or other code readers may doubt why
need 'end'.


2014-10-13  Chen Gang  <gang.chen.5i5j@gmail.com>

	* i387-tdep.c (i387_supply_fsave): Avoid warning for
	"-Werror=strict-overflow"
---
 gdb/i387-tdep.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/gdb/i387-tdep.c b/gdb/i387-tdep.c
index d66ac6a..f39c090 100644
--- a/gdb/i387-tdep.c
+++ b/gdb/i387-tdep.c
@@ -450,11 +450,13 @@ i387_supply_fsave (struct regcache *regcache, int regnum, const void *fsave)
   struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   const gdb_byte *regs = fsave;
-  int i;
+  int i, end;
 
   gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);
 
-  for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
+  /* Avoid -Werror=strict-overflow for (X + c) >= X, so use 'end' */
+  end = I387_ST0_REGNUM (tdep) + I387_NUM_REGS;
+  for (i = I387_ST0_REGNUM (tdep); i < end; i++)
     if (regnum == -1 || regnum == i)
       {
 	if (fsave == NULL)
@@ -503,11 +505,13 @@ i387_collect_fsave (const struct regcache *regcache, int regnum, void *fsave)
 {
   struct gdbarch_tdep *tdep = gdbarch_tdep (get_regcache_arch (regcache));
   gdb_byte *regs = fsave;
-  int i;
+  int i, end;
 
   gdb_assert (tdep->st0_regnum >= I386_ST0_REGNUM);
 
-  for (i = I387_ST0_REGNUM (tdep); i < I387_XMM0_REGNUM (tdep); i++)
+  /* Avoid -Werror=strict-overflow for (X + c) >= X, so use 'end' */
+  end = I387_ST0_REGNUM (tdep) + I387_NUM_REGS;
+  for (i = I387_ST0_REGNUM (tdep); i < end; i++)
     if (regnum == -1 || regnum == i)
       {
 	/* Most of the FPU control registers occupy only 16 bits in
-- 
1.8.5.2 (Apple Git-48)