Type-Based Alias Analysis
By Mark Mitchell, October 01, 2000
Aliasing issues make it difficult for compilers to generate code that runs as fast as you might hope. Luckily, the C++ type system makes clear what can and cannot alias.
Oct00: Type-Based Alias Analysis
<b>(a) </b>
void f (int ip1[], int ip2[]) {
int i;
for (i = 0; i < 9; ++i) {
ip1[i + 1] = ip2[i] + ip2[i + 1];
}
}
<b>(b) </b>
LOAD r1, ip2[0]
LOAD r2, ip2[1]
ADD r3, r1, r2 # Add ip2[0] and ip2[1].
STORE ip1[1], r3 # Store result in ip1[1].
LOAD r1, ip2[2]
ADD r3, r1, r2 # Add ip2[1] and ip2[2].
STORE ip1[2], r3 # Store result in ip1[2].
LOAD r2, ip2[3]
ADD r3, r1, r2 # Add ip2[2] and ip2[3].
STORE ip1[3], r3 # Store result in ip1[3].
...
<b>(c) </b>
LOAD r1, ip2[0]
LOAD r2, ip2[1]
ADD r3, r1, r2 # Add ip2[0] and ip2[1].
STORE ip1[1], r3 # Store result in ip1[1].
LOAD r1, ip2[1]
LOAD r2, ip2[2]
ADD r3, r1, r2 # Add ip2[1] and ip2[2].
STORE ip1[2], r3 # Store result in ip1[2].
LOAD r1, ip2[2]
LOAD r2, ip2[3]
ADD r3, r1, r2 # Add ip2[2] and ip2[3].
STORE ip1[3], r3 # Store result in ip1[3].
...
Example 2: Simple function. (a) C source code; (b) assembly code, assuming no aliasing; (c) assembly code, assuming aliasing.
