[Bug optimization/11832] New: Optimization of common code in switch statements

["alga at rgai dot hu" <gcc-bugzilla@gcc.gnu.org>]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11832

           Summary: Optimization of common code in switch statements
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: alga at rgai dot hu
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: arm-unknown-elf

If a C switch statement contains common code among certain case branches,
GCC isn't able to combine the common code.
Reorganization of the switch may solve this problem.

--- c example ---
int a, b, e;
unsigned char *c;
void foo()
{
  int d = 13;
  b = -1;   
  switch (e) {
    case 1:
      b++; c[b] = (unsigned char)d;
      break;
    case 2:
      b++; c[b] = (unsigned char)d;
      b++; c[b] = (unsigned char)d;
      break;
    case 3:
      b++; c[b] = (unsigned char)d;
      b++; c[b] = (unsigned char)d;
      b++; c[b] = (unsigned char)d;
      break;
    default:
      a = 1;
      b++; c[b] = (unsigned char)d;
      b++; c[b] = (unsigned char)d;
      b++; c[b] = (unsigned char)d;
      b++; c[b] = (unsigned char)d;
  }
}

--- arm code ---
foo:
 stmfd sp!, {r4, lr}
 ldr r3, .L10
 ldr r2, [r3, #0]
 ldr lr, .L10+4
 mvn r3, #0
 cmp r2, #2
 str r3, [lr, #0]
 mov r4, #13
 beq .L4
 bgt .L7
 cmp r2, #1
 beq .L3
 b .L6
.L7:
 cmp r2, #3
 beq .L5
 b .L6
.L3:
 ldr r3, .L10+8
 ldr r2, [r3, #0]
 mov r3, #0
 str r3, [lr, #0]
 strb r4, [r2, #0]
 ldmfd sp!, {r4, pc}
.L4:
 ldr r1, .L10+8
 ldr r2, [r1, #0]
 mov r3, #0
 str r3, [lr, #0]
 strb r4, [r2, #0]
 ldr r3, [lr, #0]
 ldr r2, [r1, #0]
 b .L8
.L5:
 ldr r2, .L10+8
 ldr r1, [r2, #0]
 mov r3, #0
 str r3, [lr, #0]
 strb r4, [r1, #0]
 ldr r3, [lr, #0]
 ldr r1, [r2, #0]
 add r3, r3, #1
 str r3, [lr, #0]
 strb r4, [r1, r3]
 ldr r3, [lr, #0]
 ldr r2, [r2, #0]
.L8:
 add r3, r3, #1
.L9:
 str r3, [lr, #0]
 strb r4, [r2, r3]
 ldmfd sp!, {r4, pc}
.L6:
 ldr r0, .L10+8
 ldr r2, [lr, #0]
 ldr ip, [r0, #0]
 ldr r3, .L10+12
 mov r1, #1
 add r2, r2, #1
 str r2, [lr, #0]
 str r1, [r3, #0]
 strb r4, [ip, r2]
 ldr r3, [lr, #0]
 ldr r2, [r0, #0]
 add r3, r3, r1
 str r3, [lr, #0]
 strb r4, [r2, r3]
 ldr r3, [lr, #0]
 ldr r2, [r0, #0]
 add r3, r3, r1
 str r3, [lr, #0]
 strb r4, [r2, r3]
 ldr r3, [lr, #0]
 ldr r2, [r0, #0]
 add r3, r3, r1
 b .L9