1. Common Subexpression Elimination and Copy Propagation in Titanium
Johnathon Jamison
David Marin
CS265
S. Graham

7. Global Copy Propagation
Given
a = b; …
x = a + 1;
We want to replace a with b on the last line, but we need to know that a and b are unchanged
Def/use analysis isn’t quite enough (why?)

8. Inserting Fake Defs and Uses
Add fake defs and uses so that def/use analysis gives us the info we need
b = b;
a = b; …
newtemp = b;
x = a + 1;

19. Interaction with Copy Propagation
Any temps introduced are placed after the calculation, so that copy propagation can remove them
a = f * i a = f * i
temp_1 = a
… …
b = f * i b = temp_1
temp_2 = b
c = f * i c = temp_2

23. Local CSE Used Muchnick’s algorithm (described in class)
Used defs to find what was killed
Fully implemented
Except method calls
Since we are using defs already, why not so something more substantial?