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RISC-V/libgcc: Reduce the size of RV64 millicode by 6 bytes 

Rewrite code sequences throughout the 64-bit RISC-V `__riscv_save_*'
routines replacing `li t1, -48', `li t1, -64', and `li t1, -80',
instructions, which do not have a compressed encoding, respectively with
`li t1, 3', `li t1, 4', and `li t1, 4', which do, and then adjusting the
remaining code accordingly observing that `sub sp, sp, t1' takes the
same amount of space as an `slli t1, t1, 4'/`add sp, sp, t1' instruction
pair does, again due to the use of compressed encodings, saving 6 bytes
total.

This change does increase code size by 4 bytes for RISC-V processors
lacking the compressed instruction set, however their users couldn't
care about the code size or they would have chosen an implementation
that does have the compressed instructions, wouldn't they?

	libgcc/
	* config/riscv/save-restore.S [__riscv_xlen == 64]
	(__riscv_save_10, __riscv_save_8, __riscv_save_6, __riscv_save_4)
	(__riscv_save_2): Replace negative immediates used for the final
	stack pointer adjustment with positive ones, right-shifted by 4.
This commit is contained in:
Maciej W. Rozycki 2020-07-31 23:52:20 +01:00
parent d1da25fe99
commit 9fa4023c7a
1 changed files with 7 additions and 6 deletions
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13
libgcc/config/riscv/save-restore.S
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@ -45,7 +45,7 @@ FUNC_BEGIN (__riscv_save_10)
.cfi_restore 27
addi sp, sp, -112
.cfi_def_cfa_offset 112
li t1, -16
li t1, 1
.Ls10:
sd s10, 16(sp)
.cfi_offset 26, -96
@ -60,7 +60,7 @@ FUNC_BEGIN (__riscv_save_8)
.cfi_restore 27
addi sp, sp, -112
.cfi_def_cfa_offset 112
li t1, -32
li t1, 2
.Ls8:
sd s8, 32(sp)
.cfi_offset 24, -80
@ -77,7 +77,7 @@ FUNC_BEGIN (__riscv_save_6)
.cfi_restore 27
addi sp, sp, -112
.cfi_def_cfa_offset 112
li t1, -48
li t1, 3
.Ls6:
sd s6, 48(sp)
.cfi_offset 22, -64
@ -99,7 +99,7 @@ FUNC_BEGIN (__riscv_save_4)
.cfi_restore 27
addi sp, sp, -112
.cfi_def_cfa_offset 112
li t1, -64
li t1, 4
.Ls4:
sd s4, 64(sp)
.cfi_offset 20, -48
@ -123,7 +123,7 @@ FUNC_BEGIN (__riscv_save_2)
.cfi_restore 27
addi sp, sp, -112
.cfi_def_cfa_offset 112
li t1, -80
li t1, 5
.Ls2:
sd s2, 80(sp)
.cfi_offset 18, -32
@ -133,9 +133,10 @@ FUNC_BEGIN (__riscv_save_2)
.cfi_offset 8, -16
sd ra, 104(sp)
.cfi_offset 1, -8
slli t1, t1, 4
# CFA info is not correct in next 2 instruction since t1's
# value is depend on how may register really save.
sub sp, sp, t1
add sp, sp, t1
jr t0
.cfi_endproc
FUNC_END (__riscv_save_12)