While doing some size measurements and optimization I found that using the
t0 through t7 registers on MIPS in MIPS16 mode resulted in larger code. This
is because you cannot actually do any operations on these registers in MIPS16
mode but can only move data to or from them. Compiling libraries like libjpeg
and libpng with this change saved about 1% in space. I also ran coremark, the
space saving there was smaller and the performance slowdown was around 3% so
I made the change dependent on the optimize_size flag.
I tested the change with the mips-mti-elf, running the GCC testsuite with the
-mips16 and saw no regressions. OK to checkin?
Steve Ellcey
sell...@mips.com
Steve Ellcey <sell...@mips.com>
* config/mips/mips.c (mips_conditional_register_usage): Do not
use t[0-7] registers in MIPS16 mode when optimizing for size.
diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index bd1d10b..fb89aa8 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -17213,6 +17213,21 @@ mips_conditional_register_usage (void)
fixed_regs[27] = call_used_regs[27] = 1;
fixed_regs[30] = call_used_regs[30] = 1;
+ /* In MIPS16 mode using the $t registers for reload results in code
+ that is larger (and slightly faster) then if we do not use them so
+ if optimizing for size, do not use them. */
+ if (optimize_size)
+ {
+ fixed_regs[8] = call_used_regs[8] = 1;
+ fixed_regs[9] = call_used_regs[9] = 1;
+ fixed_regs[10] = call_used_regs[10] = 1;
+ fixed_regs[11] = call_used_regs[11] = 1;
+ fixed_regs[12] = call_used_regs[12] = 1;
+ fixed_regs[13] = call_used_regs[13] = 1;
+ fixed_regs[14] = call_used_regs[14] = 1;
+ fixed_regs[15] = call_used_regs[15] = 1;
+ }
+
/* Do not allow HI and LO to be treated as register operands.
There are no MTHI or MTLO instructions (or any real need
for them) and one-way registers cannot easily be reloaded. */
