https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105733
Vineet Gupta <vineetg at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |vineetg at gcc dot gnu.org
--- Comment #4 from Vineet Gupta <vineetg at gcc dot gnu.org> ---
There has been good improvements in gcc codegen specially with commit below.
commit 6619b3d4c15cd754798b1048c67f3806bbcc2e6d
Author: Jivan Hakobyan <jivanhakoby...@gmail.com>
Date: Wed Aug 23 14:10:30 2023 -0600
Improve quality of code from LRA register elimination
This is primarily Jivan's work, I'm mostly responsible for the write-up and
coordinating with Vlad on a few questions.
On targets with limitations on immediates usable in arithmetic
instructions,
LRA's register elimination phase can construct fairly poor code.
Tip W/o commit 6619b3d4c | With 6619b3d4c
|
foo: | foo:
li t0,-4096 | li t0,-4096
addi t0,t0,2032 | addi t0,t0,2032
li a5,0 |
li a4,0 |
add sp,sp,t0 | add sp,sp,t0
add a4,a4,a5 |
add a5,a4,sp | add a5,a5,a0
add a5,a5,a0 |
li t0,4096 | li t0,4096
sb zero,0(a5) | sb zero,0(a5)
addi t0,t0,-2032 | addi t0,t0,-2032
add sp,sp,t0 | add sp,sp,t0
jr ra | jr ra
We still have the weird LUI 4096 based constant construction. I have a patch to
avoid 4096 for certain ranges [-4096,-2049] or [2048,4094] (cribbed from
llvm).
e.g. 2064 = 2047 + 17 and we could potentially "spread" the 2 parts over 2 adds
to SP, avoiding the LUI. However if a const costs more than 1 insn, gcc wants
to force it in a register rather than split the add operation into 2 adds with
the split constants.
expand_binop
expand_binop_directly
avoid_expensive_constant
/* X is to be used in mode MODE as operand OPN to BINOPTAB. If we're
optimizing, and if the operand is a constant that costs more than
1 instruction, force the constant into a register and return that
register. Return X otherwise. UNSIGNEDP says whether X is unsigned. */
