Branch on ?: operator?

Question

For a typical modern compiler on modern hardware, will the ? : operator result in a branch that affects the instruction pipeline?

In other words which i

Answer 1

The CMOV (Conditional MOVe) instruction has been part of the x86 instruction set since the Pentium Pro. It is rarely automatically generated by GCC because of compiler options commonly used and restrictions placed by the C language. A SETCC/CMOV sequence can be inserted by inline assembly in your C program. This should only be done is cases where the conditional variable is a randomly oscillating value in the inner loop (millions of executions) of a program. In non-oscillating cases and in cases of simple patterns of oscillation, modern processors can predict branches with a very high degree of accuracy. In 2007, Linus Torvalds suggested here to avoid use of CMOV in most situations.

Intel describes the conditional move in the Intel(R) Architecture Software Developer's Manual, Volume 2: Instruction Set Reference Manual:

The CMOVcc instructions check the state of one or more of the status flags in the EFLAGS
register (CF, OF, PF, SF, and ZF) and perform a move operation if the flags are in a specified
state (or condition). A condition code (cc) is associated with each instruction to indicate the
condition being tested for. If the condition is not satisfied, a move is not performed and execution
continues with the instruction following the CMOVcc instruction.

These instructions can move a 16- or 32-bit value from memory to a general-purpose register or
from one general-purpose register to another. Conditional moves of 8-bit register operands are
not supported.

The conditions for each CMOVcc mnemonic is given in the description column of the above
table. The terms “less” and “greater” are used for comparisons of signed integers and the terms
“above” and “below” are used for unsigned integers.

Because a particular state of the status flags can sometimes be interpreted in two ways, two
mnemonics are defined for some opcodes. For example, the CMOVA (conditional move if
above) instruction and the CMOVNBE (conditional move if not below or equal) instruction are
alternate mnemonics for the opcode 0F 47H.