[Bug inline-asm/37562] New: [4.2] -funroll-loops destroys inline asm code von powerpc

[rbuergel at web dot de]

typedef unsigned int UInt32;
typedef unsigned char UInt8;

struct Data
{
  UInt8 data[16];

  const UInt8* getData() const
  {
    return data + 4;
  }
};

struct Value {
  UInt32 value;
  static void update (Value& signal, const Data& source, UInt32 startBit);
};

void Value::update(Value& signal, const Data& source, UInt32 startByte)
{
  UInt32& value = signal.value;
  const UInt8* data = source.getData();
  asm( "lwbrx %0,%1,%2;\n":"=r"(value): "r"(data), "r"(startByte), "m" (*(data
+ startByte)) );
}

generated for gcc-4.2.4 on powerpc:
00000000 <_ZN5Value6updateERS_RK4Dataj>:
   0:   38 04 00 04     addi    r0,r4,4
   4:   7c 80 2c 2c     lwbrx   r4,0,r5
   8:   90 83 00 00     stw     r4,0(r3)
   c:   4e 80 00 20     blr

the correct version without -funroll-loops reads:
00000000 <_ZN5Value6updateERS_RK4Dataj>:
   0:   38 84 00 04     addi    r4,r4,4
   4:   7c 84 2c 2c     lwbrx   r4,r4,r5
   8:   90 83 00 00     stw     r4,0(r3)
   c:   4e 80 00 20     blr


lwbrx sums the contents of r4 and r5 and accesses this address, swaps it's
value and stores it again in r4. The incorrect version accesses an invalid
address, which leads to a segmentation fault.

this is corrected at least with gcc-4.3.1, there i couldn't reproduce the
behaviour.


-- 
           Summary: [4.2] -funroll-loops destroys inline asm code von
                    powerpc
           Product: gcc
           Version: 4.2.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rbuergel at web dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37562