This patch improves the allocation of registers in the given function. The allocation
is optimized for the conditional branches. The temporary register used in the
conditional branches to store the comparison results and use of temporary in the
conditional branch is optimized. Such temporary registers are allocated with a fixed
register r18.

Currently such temporaries are allocated with a free registers in the given
function. Due to this one of the free register is reserved for the temporaries and
given function is left with a few registers. This is unoptimized with respect to
microblaze. In Microblaze r18 is marked as fixed and cannot be allocated to pseudos'
in the given function. Instead r18 can be used as a temporary for the conditional
branches with compare and branch. Use of r18 as a temporary for conditional branches
will save one of the free registers to be allocated. The free registers can be used
for other pseudos' and hence the better register allocation.

The usage of r18 as above reduces the spill and fetch because of the availability of
one of the free registers to other pseudos instead of being used for conditional
temporaries.

The advantage of the above is that the scope of the temporaries is limited to the
conditional branches and hence the usage of r18 as temporary for such conditional
branches is optimized and preserve the functionality of the function.

Regtested for Microblaze target.

Performance runs are done with Mibench/EEMBC benchmarks.

Following gains are achieved.

Benchmarks                  Gains

automotive_qsort1   1.630730524%
network_dijkstra       1.527506256%
office_stringsearch   1 1.81356288%
security_rijndael_d   3.26129357%
basefp01_lite              4.465120185%
a2time01_lite              1.893862857%
cjpeg_lite                      3.286496675%
djpeg_lite                     3.120150612%
qos_lite                         2.63964381%
office_ispell                 1.531340405%

Code Size improvements:

Reduction in number of instructions for Mibench  :  12927.
Reduction in number of instructions for EEMBC :   212.

ChangeLog:
2016-01-29  Ajit Agarwal  <ajitkum@xilinx.com>

	* config/microblaze/microblaze.c
	(microblaze_expand_conditional_branch): Use of MB_ABI_ASM_TEMP_REGNUM
	for temporary conditional branch.
	(microblaze_expand_conditional_branch_reg): Use of MB_ABI_ASM_TEMP_REGNUM
	for temporary conditional branch.
	(microblaze_expand_conditional_branch_sf): Use of MB_ABI_ASM_TEMP_REGNUM
	for temporary conditional branch.

Signed-off-by:Ajit Agarwal ajitkum@xilinx.com.
---
 gcc/config/microblaze/microblaze.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/gcc/config/microblaze/microblaze.c b/gcc/config/microblaze/microblaze.c
index baff67a..b4277ad 100644
--- a/gcc/config/microblaze/microblaze.c
+++ b/gcc/config/microblaze/microblaze.c
@@ -3402,7 +3402,7 @@ microblaze_expand_conditional_branch (machine_mode mode, rtx operands[])
   rtx cmp_op0 = operands[1];
   rtx cmp_op1 = operands[2];
   rtx label1 = operands[3];
-  rtx comp_reg = gen_reg_rtx (SImode);
+  rtx comp_reg =  gen_rtx_REG (SImode, MB_ABI_ASM_TEMP_REGNUM);
   rtx condition;
 
   gcc_assert ((GET_CODE (cmp_op0) == REG) || (GET_CODE (cmp_op0) == SUBREG));
@@ -3439,7 +3439,7 @@ microblaze_expand_conditional_branch_reg (enum machine_mode mode,
   rtx cmp_op0 = operands[1];
   rtx cmp_op1 = operands[2];
   rtx label1 = operands[3];
-  rtx comp_reg = gen_reg_rtx (SImode);
+  rtx comp_reg =  gen_rtx_REG (SImode, MB_ABI_ASM_TEMP_REGNUM);
   rtx condition;
 
   gcc_assert ((GET_CODE (cmp_op0) == REG)
@@ -3483,7 +3483,7 @@ microblaze_expand_conditional_branch_sf (rtx operands[])
   rtx condition;
   rtx cmp_op0 = XEXP (operands[0], 0);
   rtx cmp_op1 = XEXP (operands[0], 1);
-  rtx comp_reg = gen_reg_rtx (SImode);
+  rtx comp_reg =  gen_rtx_REG (SImode, MB_ABI_ASM_TEMP_REGNUM);
 
   emit_insn (gen_cstoresf4 (comp_reg, operands[0], cmp_op0, cmp_op1));
   condition = gen_rtx_NE (SImode, comp_reg, const0_rtx);
-- 
1.7.1

Thanks & Regards
Ajit