-fverbose-asm
Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself).

-O3

gcc -O3 -fverbose-asm -o t.s t.c

	.arch armv8-a
	.file	"t.c"
// GNU C17 (GCC) version 9.2.0 (aarch64-unknown-linux-gnu)
//	compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 4.0.2, MPC version 1.1.0, isl version isl-0.21-GMP

// GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
// options passed:  t.c -march=armv8-a -mlittle-endian -mabi=lp64
// -auxbase-strip 3 -O3 -fverbose-asm
// options enabled:  -fPIC -fPIE -faggressive-loop-optimizations
// -falign-functions -falign-jumps -falign-labels -falign-loops
// -fassume-phsa -fasynchronous-unwind-tables -fauto-inc-dec
// -fbranch-count-reg -fcaller-saves -fcode-hoisting
// -fcombine-stack-adjustments -fcommon -fcompare-elim -fcprop-registers
// -fcrossjumping -fcse-follow-jumps -fdefer-pop
// -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively
// -fdwarf2-cfi-asm -fearly-inlining -feliminate-unused-debug-types
// -fexpensive-optimizations -fforward-propagate -ffp-int-builtin-inexact
// -ffunction-cse -fgcse -fgcse-after-reload -fgcse-lm -fgnu-runtime
// -fgnu-unique -fguess-branch-probability -fhoist-adjacent-loads -fident
// -fif-conversion -fif-conversion2 -findirect-inlining -finline
// -finline-atomics -finline-functions -finline-functions-called-once
// -finline-small-functions -fipa-bit-cp -fipa-cp -fipa-cp-clone -fipa-icf
// -fipa-icf-functions -fipa-icf-variables -fipa-profile -fipa-pure-const
// -fipa-ra -fipa-reference -fipa-reference-addressable -fipa-sra
// -fipa-stack-alignment -fipa-vrp -fira-hoist-pressure
// -fira-share-save-slots -fira-share-spill-slots
// -fisolate-erroneous-paths-dereference -fivopts -fkeep-static-consts
// -fleading-underscore -flifetime-dse -floop-interchange
// -floop-unroll-and-jam -flra-remat -flto-odr-type-merging -fmath-errno
// -fmerge-constants -fmerge-debug-strings -fmove-loop-invariants
// -fomit-frame-pointer -foptimize-sibling-calls -foptimize-strlen
// -fpartial-inlining -fpeel-loops -fpeephole -fpeephole2 -fplt
// -fpredictive-commoning -fprefetch-loop-arrays -free -freg-struct-return
// -freorder-blocks -freorder-functions -frerun-cse-after-loop
// -fsched-critical-path-heuristic -fsched-dep-count-heuristic
// -fsched-group-heuristic -fsched-interblock -fsched-last-insn-heuristic
// -fsched-pressure -fsched-rank-heuristic -fsched-spec
// -fsched-spec-insn-heuristic -fsched-stalled-insns-dep -fschedule-fusion
// -fschedule-insns -fschedule-insns2 -fsection-anchors
// -fsemantic-interposition -fshow-column -fshrink-wrap
// -fshrink-wrap-separate -fsigned-zeros -fsplit-ivs-in-unroller
// -fsplit-loops -fsplit-paths -fsplit-wide-types -fssa-backprop
// -fssa-phiopt -fstack-protector-strong -fstdarg-opt -fstore-merging
// -fstrict-aliasing -fstrict-volatile-bitfields -fsync-libcalls
// -fthread-jumps -ftoplevel-reorder -ftrapping-math -ftree-bit-ccp
// -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-coalesce-vars
// -ftree-copy-prop -ftree-cselim -ftree-dce -ftree-dominator-opts
// -ftree-dse -ftree-forwprop -ftree-fre -ftree-loop-distribute-patterns
// -ftree-loop-distribution -ftree-loop-if-convert -ftree-loop-im
// -ftree-loop-ivcanon -ftree-loop-optimize -ftree-loop-vectorize
// -ftree-parallelize-loops= -ftree-partial-pre -ftree-phiprop -ftree-pre
// -ftree-pta -ftree-reassoc -ftree-scev-cprop -ftree-sink
// -ftree-slp-vectorize -ftree-slsr -ftree-sra -ftree-switch-conversion
// -ftree-tail-merge -ftree-ter -ftree-vrp -funit-at-a-time
// -funswitch-loops -funwind-tables -fverbose-asm
// -fversion-loops-for-strides -fzero-initialized-in-bss
// -mfix-cortex-a53-835769 -mfix-cortex-a53-843419 -mglibc -mlittle-endian
// -momit-leaf-frame-pointer -mpc-relative-literal-loads

	.text
	.ident	"GCC: (GNU) 9.2.0"
	.section	.note.GNU-stack,"",@progbits

-Og

gcc -Og -fverbose-asm -o t.s t.c

	.arch armv8-a
	.file	"t.c"
// GNU C17 (GCC) version 9.2.0 (aarch64-unknown-linux-gnu)
//	compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 4.0.2, MPC version 1.1.0, isl version isl-0.21-GMP

// GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
// options passed:  t.c -march=armv8-a -mlittle-endian -mabi=lp64
// -auxbase-strip 3 -Og -fverbose-asm
// options enabled:  -fPIC -fPIE -faggressive-loop-optimizations
// -fassume-phsa -fasynchronous-unwind-tables -fauto-inc-dec
// -fcombine-stack-adjustments -fcommon -fcompare-elim -fcprop-registers
// -fdefer-pop -fdelete-null-pointer-checks -fdwarf2-cfi-asm
// -fearly-inlining -feliminate-unused-debug-types -fforward-propagate
// -ffp-int-builtin-inexact -ffunction-cse -fgcse-lm -fgnu-runtime
// -fgnu-unique -fguess-branch-probability -fident -finline
// -finline-atomics -fipa-profile -fipa-pure-const -fipa-reference
// -fipa-reference-addressable -fipa-stack-alignment -fira-hoist-pressure
// -fira-share-save-slots -fira-share-spill-slots -fivopts
// -fkeep-static-consts -fleading-underscore -flifetime-dse
// -flto-odr-type-merging -fmath-errno -fmerge-constants
// -fmerge-debug-strings -fomit-frame-pointer -fpeephole -fplt
// -fprefetch-loop-arrays -freg-struct-return -freorder-blocks
// -fsched-critical-path-heuristic -fsched-dep-count-heuristic
// -fsched-group-heuristic -fsched-interblock -fsched-last-insn-heuristic
// -fsched-pressure -fsched-rank-heuristic -fsched-spec
// -fsched-spec-insn-heuristic -fsched-stalled-insns-dep -fschedule-fusion
// -fsection-anchors -fsemantic-interposition -fshow-column -fshrink-wrap
// -fshrink-wrap-separate -fsigned-zeros -fsplit-ivs-in-unroller
// -fsplit-wide-types -fssa-backprop -fstack-protector-strong -fstdarg-opt
// -fstrict-volatile-bitfields -fsync-libcalls -ftoplevel-reorder
// -ftrapping-math -ftree-builtin-call-dce -ftree-ccp -ftree-ch
// -ftree-coalesce-vars -ftree-copy-prop -ftree-cselim -ftree-dce
// -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre
// -ftree-loop-if-convert -ftree-loop-im -ftree-loop-ivcanon
// -ftree-loop-optimize -ftree-parallelize-loops= -ftree-phiprop
// -ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-ter
// -funit-at-a-time -funwind-tables -fverbose-asm -fzero-initialized-in-bss
// -mfix-cortex-a53-835769 -mfix-cortex-a53-843419 -mglibc -mlittle-endian
// -momit-leaf-frame-pointer -mpc-relative-literal-loads

	.text
	.ident	"GCC: (GNU) 9.2.0"
	.section	.note.GNU-stack,"",@progbits

References
GCC Options – https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html