Compile the attached code with options -march=armv7-a -mthumb -Os -fpic, gcc
generates:
foo3:
push {r4, r5, r6, r7, lr}
sub sp, sp, #12 // A
ldr r3, .L4
add r7, sp, #0 // B
sub sp, sp, #48 // C
mov r0, sp
...
Instruction A is used to allocate space for spilled variables. Instruction B
setups a frame pointer. Instruction C allocate space for local variables.
Instruction A and C can be merged into one, so ABC can be rewritten as:
sub sp, sp, 60
add r7, sp, r8
Instruction C is emitted at the expand phase. But instructions AB is emitted
from function arm_expand_prologue in pro_and_epilogue pass. So one possible
solution is stop emitting code to allocate space for local variables. Instead
record the local variables' space size and allocate the space with spill space
together in pro_and_epilogue pass.
--
Summary: The stack pointer is adjusted twice
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: carrot at google dot com
GCC build triplet: i686-linux
GCC host triplet: i686-linux
GCC target triplet: arm-eabi
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43513
