https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105733
Vineet Gupta <vineetg at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- 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. */