Question about gimple code during optimizing if-conversion

[Hanke Zhang via Gcc]

Hi, I'm working on optimizing if-conversion for my own business
recently. I got a problem here.

I tried to optimize it in such a case, for example, when a conditional
statement block has only if statement and no else statement, the
source C code looks like this:

int* foo; // assume this has been initialized
int c = rand(), t = rand(), size = 10000000;
for (int i = 0; i < size; i++) {
  if (foo[i] & (1 << c)) foo[i] ^= (1 << t);
}

Part of its corresponding gimple is optimized like this before if-conversion:

  <bb 5>:
  # i_71 = PHI <i_39(12), 0(9)>
  # ivtmp_9 = PHI <ivtmp_73(12), 10000000(9)>
  _5 = (long unsigned int) i_71;
  _6 = _5 * 4;
  _7 = foo_23 + _6;
  _8 = *_7;
  shifttmp_75 = _8 & shifttmp_76;
  if (shifttmp_75 != 0)
    goto <bb 6>; [50.00%]
  else
    goto <bb 14>; [50.00%]

  <bb 14> [local count: 531502205]:
  goto <bb 7>; [100.00%]

  <bb 6> [local count: 531502204]:
  _12 = _8 ^ _11;
  *_7 = _12;

  <bb 7> [local count: 1063004409]:
  i_39 = i_71 + 1;
  ivtmp_73 = ivtmp_9 - 1;
  if (ivtmp_73 != 0)
    goto <bb 12>; [99.00%]
  else
    goto <bb 8>; [1.00%]

I want to add some statements to gimple to make it like adding an else
block to the source code.

// What I expected:
int* foo; // assume this has been initialized
int c = rand(), t = rand(), size = 10000000;
for (int i = 0; i < size; i++) {
  if (foo[i] & (1 << c)) foo[i] ^= (1 << t);
+  else foo[i] = foo[i];  // I want to add a statment here !!!!!
}

And of course I can't change the source code for real, so I can only
add a pass in front of if-conversion to modify the gimple.

For the example above, I know that I have to add them in the block
'<bb14>', but what confuses me is that I don't know what kind of
statement to add to be legal due to my poor experience.

I try to add something like this below, but the compile error just
happened. So I'm here for help. What kind of statements should I add
here?

<bb 14> [local count: 531502205]:
+ *_7 = *_7
 goto <bb 7>; [100.00%]

Finally, The reason I did this was to avoid MASK_STORE generation,
because it might add an if branch in the final assembly which I don't
like it to be. And after such a modification, if-conversion should
have been changed it to the form of a ternary expression, which would
reduce the occurrence of branches after final vectorization and
produce more efficient code.

Or there if is a better way to get rid of MASK_STORE, please tell me
about that. :)

Thanks
Hanke Zhang