Compilation and Execution Differences

While the Intel® C++ Compiler is compatible with the Microsoft* Visual C++* compiler, some differences can prevent successful compilation. Also there can be some incompatible generated-code behavior of some source files with the Intel® C++ Compiler. In most cases, a modification of the user source file enables successful compilation with both the Intel® C++ Compiler and the Microsoft* Visual C++* compiler. The differences between the compilers are listed as follows:

Evaluation of Left Shift Operations

The Intel® C++ Compiler differs from the Microsoft* Visual C++* compiler in the evaluation of left shift operations where the right operand, or shift count, is equal to or greater than the size of the left operand expressed in bits. The ANSI C standard states that the behavior of such left-shift operations is undefined, meaning a program should not expect a certain behavior from these operations. This difference is only evident when both operands of the shift operation are constants. The following example illustrates this difference between the Intel® C++ Compiler and the Microsoft* Visual C++* compiler:

int x; 
int y = 1; //set y=1 
void func() {
  x = 1 << 32;
  // Intel C++ Compiler generates code to set x=1
  // Visual C++ Compiler generates code to set x=0  

  y = y << 32;
  // Intel C++ Compiler generates code to set y=1 
  // Visual C++ Compiler generates code to set y=1
}

Inline Assembly Target Labels (IA-32 Architecture Only)

For compilations targeted for IA-32 architecture, inline assembly target labels of goto statements are case sensitive. The Microsoft* Visual C++* compiler treats these labels in a case insensitive manner. For example, the Intel® C++ Compiler issues an error when compiling the following code:

int func(int x) {
   goto LAB2;
     // error: label "LAB2" was referenced but not defined
   __asm lab2: mov x, 1
   return x;
}

However, the Microsoft* Visual C++* compiler accepts the preceding code. As a work-around for the Intel® C++ Compiler, when a goto statement refers to a label defined in inline assembly, you must match the label reference with the label definition in both name and case.