Merging identical constants

Procedure

1. Create a C source file, litpool.c, containing the following code:

   int f1() {
       return 0xdeadbeef;
   }
   int f2() {
       return 0xdeadbeef;
   }

2. Compile the source with -S to create an assembly file:
   armclang -c -S -target arm-arm-none-eabi -mcpu=cortex-m0 -ffunction-sections litpool.c -o litpool.s

   Note:

   -ffunction-sections is the default.
   Results:

   Because 0xdeadbeef is a difficult constant to create using instructions, a literal pool is created, for example:

   ...
   f1:
   	.fnstart
   @ BB#0:
   	ldr	r0, __arm_cp.0_0
   	bx	lr
   	.p2align	2
   @ BB#1:
   __arm_cp.0_0:
   	.long	3735928559              @ 0xdeadbeef
   ...
   	.fnend
   
   ...
   	.code	16                      @ @f2
   	.thumb_func
   f2:
   	.fnstart
   @ BB#0:
   	ldr	r0, __arm_cp.1_0
   	bx	lr
   	.p2align	2
   @ BB#1:
   __arm_cp.1_0:
   	.long	3735928559              @ 0xdeadbeef
   ...
   	.fnend
   ...

   Note:

   There is one copy of the constant for each function, because armclang cannot share these constants between both functions.
3. Compile the source to create an object:
   armclang -c -target arm-arm-none-eabi -mcpu=cortex-m0 litpool.c -o litpool.o
4. Link the object file using the --merge_litpools option:
   armlink --cpu=Cortex-M0 --merge_litpools litpool.o -o litpool.axf

   Note:

   --merge_litpools is the default.
5. Run fromelf to view the image structure:
   fromelf -c -d -s -t -v -z litpool.axf
   Results: The following example shows the result of the merge:

   ...
       f1
           0x00008000:    4801        .H      LDR      r0,[pc,#4] ; [0x8008] = 0xdeadbeef
           0x00008002:    4770        pG      BX       lr
       f2
           0x00008004:    4800        .H      LDR      r0,[pc,#0] ; [0x8008] = 0xdeadbeef
           0x00008006:    4770        pG      BX       lr
       $d.4
       __arm_cp.1_0
           0x00008008:    deadbeef    ....    DCD    3735928559
   ...