https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65326
renlin at gcc dot gnu.org changed:
What|Removed |Added
CC||renlin at gcc dot gnu.org
--- Comment #1 from renlin at gcc dot gnu.org ---
In this specific case, thumb_legitimize_address will generate ldr r0, [r9, r10]
pattern(after IRA). However, this pattern only allows LO_REGS. During reload,
r9r10 will be spilled into LO_REGS, that's where those two mov instructions
come from.
(In reply to Matthew Wahab from comment #0)
Created attachment 34964 [details]
Testcase showing change in behaviour.
The ARM backend no longer supports -mno-lra so only the LRA is available.
This
has also removed the Thumb mode optimiziation introduced in
https://gcc.gnu.org/ml/gcc-patches/2005-08/msg01140.html to fix PR 23436.
This turns sequences like
mov r3, r9
mov r2, r10
ldr r0, [r3, r2]
into
mov r3, r9
add r3, r3, r10
ldr r0, [r3]
which saves a register.
Attached is a contrived test case. Compiling with gcc-4.9 with -mthumb
-mno-lra
(at -O1 and higher) produces the second (better) sequence. Compiling with
gcc-4.9 or gcc-trunk with -mthumb (at -O1 and higher) produces the first
sequence. The sequences appear after the 'nop'
gcc-4.9 is
arm-none-eabi-gcc (GNU Tools for ARM Embedded Processors) 4.9.3 20141119
(release) [ARM/embedded-4_9-branch revision 218278]
trunk is:
arm-none-eabi-gcc (unknown) 5.0.0 20150217 (experimental)
