Hello all,
I am trying to use MemorySSA in my analysis and recently I got a problem about querying the clobbering memory access.
For the example below, both the loads for %c and %d have the clobbering memory access 5 = MemoryPhi({if.then,2},{if.else,4}).
I believe it can be further optimized. The stores that actually define %c are; 1 = MemoryDef(liveOnEntry) and ; 3 = MemoryDef(liveOnEntry) so the clobbering memory access for the load of %c could be another MemoryPhi({if.then,1},{if.else,3}).
I understand that it is the design of memorySSA to have a single MemoryPhi for each Basicblock but I am wondering if I want to have more precise information like this, should this be done as a part of MemSSA/Walker or should the analysis that uses MemorySSA handle this?
Thank you for your time and I am looking forward to your reply.
Best,
Hao
int foo(int a, int b, int m){
int c;
int d;
if(m){
c = a;
d = b;
}else{
c = a;
d = b;
}
return c+d;
}
Corresponding IR and MemSSA dump:
define dso_local i32 @foo(i32 %a, i32 %b, i32 %m) {
entry:
%c = alloca i32, align 4
%d = alloca i32, align 4
%tobool = icmp ne i32 %m, 0
br i1 %tobool, label %if.then, label %if.else
if.then: ; preds = %entry
; 1 = MemoryDef(liveOnEntry)
store i32 %a, i32* %c, align 4
; 2 = MemoryDef(1)
store i32 %b, i32* %d, align 4
br label %if.end
if.else: ; preds = %entry
; 3 = MemoryDef(liveOnEntry)
store i32 %a, i32* %c, align 4
; 4 = MemoryDef(3)
store i32 %b, i32* %d, align 4
br label %if.end
if.end: ; preds = %if.else, %if.then
; 5 = MemoryPhi({if.then,2},{if.else,4})
; MemoryUse(5) MayAlias
%0 = load i32, i32* %c, align 4
; MemoryUse(5) MayAlias
%1 = load i32, i32* %d, align 4
%add = add nsw i32 %0, %1
ret i32 %add
}