[Bug middle-end/42233] [4.3/4.4/4.5 regression] c++ builtin_expect code generation regression

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2010-02-18 12:47 -------
Created an attachment (id=19906)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19906&action=view)
gcc45-pr42233.patch

The reason why it behaves differently with __builtin_expect from normal
condition is that in the latter case gimple_boolify changes the types of the
comparisons etc. to _Bool, while for __builtin_expect it doesn't recurse into
its first argument.
The attached patch fixes that.
Then we are back to the 4.3 generated code, i.e. the same as is generated
without __builtin_expect.
At this point the problem is described in a comment above add_reg_br_prob_note:
/* Verify that there is exactly single jump instruction since last and attach
   REG_BR_PROB note specifying probability.
   ??? We really ought to pass the probability down to RTL expanders and let it
   re-distribute it when the conditional expands into multiple conditionals.
   This is however difficult to do.  */
Since here there are two jumps, not one, no REG_BR_PROB note is added.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42233