[Bug c++/42233] New: c++ builtin_expect code generation regression

[gmorin1 at bloomberg dot net]

The following c/++ code generates assembly that favors the unlikely case with
gcc 4.3 and 4.4:
extern void likely();
extern void unlikely();
void test_expect(char * a, char *b, char *c, char *d) {
    if (__builtin_expect(!!(a == b && c == d), 1)) {
        likely();
    }
    else {
        unlikely();
    }
}
Compiled with g++44 -O2 -S -fverbose-asm -m32. (or -m64).

A few notes: gcc 4.1 seems to generate better assembly.  If this code is code
is compiled as c code and not C++ with gcc 4.4, the likely case is properly
favored.

Changing the if statement into "if (__builtin_expect(!!(a == b),1) &&
__builtin_expect(!!(c == d), 1))" fixes the problem as well.  With this code,
gcc generates better code for the likely case.


-- 
           Summary: c++ builtin_expect code generation regression
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gmorin1 at bloomberg dot net


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