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48f0f2dd73
This patch teaches the caching MemorySSA walker a few things:
1. Not to walk Phis we've walked before. It seems that we tried to do
this before, but it didn't work so well in cases like:
define void @foo() {
%1 = alloca i8
%2 = alloca i8
br label %begin
begin:
; 3 = MemoryPhi({%0,liveOnEntry},{%end,2})
; 1 = MemoryDef(3)
store i8 0, i8* %2
br label %end
end:
; MemoryUse(?)
load i8, i8* %1
; 2 = MemoryDef(1)
store i8 0, i8* %2
br label %begin
}
Because we wouldn't put Phis in Q.Visited until we tried to visit them.
So, when trying to optimize MemoryUse(?):
- We would visit 3 above
- ...Which would make us put {%0,liveOnEntry} in Q.Visited
- ...Which would make us visit {%0,liveOnEntry}
- ...Which would make us put {%end,2} in Q.Visited
- ...Which would make us visit {%end,2}
- ...Which would make us visit 3
- ...Which would realize we've already visited everything in 3
- ...Which would make us conservatively return 3.
In the added test-case, (@looped_visitedonlyonce) this behavior would
cause us to give incorrect results. Specifically, we'd visit 4 twice
in the same query, but on the second visit, we'd skip while.cond because
it had been visited, visit if.then/if.then2, and cache "1" as the
clobbering def on the way back.
2. If we try to walk the defs of a {Phi,MemLoc} and see it has been
visited before, just hand back the Phi we're trying to optimize.
I promise this isn't as terrible as it seems. :)
We now insert {Phi,MemLoc} pairs just before walking the Phi's upward
defs. So, we check the cache for the {Phi,MemLoc} pair before checking
if we've already walked the Phi.
The {Phi,MemLoc} pair is (almost?) always guaranteed to have a cache
entry if we've already fully walked it, because we cache as we go.
So, if the {Phi,MemLoc} pair isn't in cache, either:
(a) we must be in the process of visiting it (in which case, we can't
give a better answer in a cache-as-we-go DFS walker)
(b) we visited it, but didn't cache it on the way back (...which seems
to require `ModifyingAccess` to not dominate `StartingAccess`,
so I'm 99% sure that would be an error. If it's not an error, I
haven't been able to get it to happen locally, so I suspect it's
rare.)
- - - - -
As a consequence of this change, we no longer skip upward defs of phis,
so we can kill the `VisitedOnlyOne` check. This gives us better accuracy
than we had before, at the cost of potentially doing a bit more work
when we have a loop.
llvm-svn: 264814
182 lines
4.4 KiB
LLVM
182 lines
4.4 KiB
LLVM
; RUN: opt -basicaa -print-memoryssa -verify-memoryssa -analyze < %s 2>&1 | FileCheck %s
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; %ptr can't alias %local, so we should be able to optimize the use of %local to
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; point to the store to %local.
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; CHECK-LABEL: define void @check
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define void @check(i8* %ptr, i1 %bool) {
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entry:
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%local = alloca i8, align 1
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; CHECK: 1 = MemoryDef(liveOnEntry)
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; CHECK-NEXT: store i8 0, i8* %local, align 1
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store i8 0, i8* %local, align 1
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br i1 %bool, label %if.then, label %if.end
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if.then:
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%p2 = getelementptr inbounds i8, i8* %ptr, i32 1
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; CHECK: 2 = MemoryDef(1)
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; CHECK-NEXT: store i8 0, i8* %p2, align 1
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store i8 0, i8* %p2, align 1
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br label %if.end
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if.end:
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; CHECK: 3 = MemoryPhi({entry,1},{if.then,2})
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; CHECK: MemoryUse(1)
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; CHECK-NEXT: load i8, i8* %local, align 1
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load i8, i8* %local, align 1
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ret void
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}
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; CHECK-LABEL: define void @check2
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define void @check2(i1 %val1, i1 %val2, i1 %val3) {
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entry:
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%local = alloca i8, align 1
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%local2 = alloca i8, align 1
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; CHECK: 1 = MemoryDef(liveOnEntry)
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; CHECK-NEXT: store i8 0, i8* %local
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store i8 0, i8* %local
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br i1 %val1, label %if.then, label %phi.3
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if.then:
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; CHECK: 2 = MemoryDef(1)
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; CHECK-NEXT: store i8 2, i8* %local2
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store i8 2, i8* %local2
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br i1 %val2, label %phi.2, label %phi.3
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phi.3:
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; CHECK: 6 = MemoryPhi({entry,1},{if.then,2})
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; CHECK: 3 = MemoryDef(6)
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; CHECK-NEXT: store i8 3, i8* %local2
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store i8 3, i8* %local2
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br i1 %val3, label %phi.2, label %phi.1
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phi.2:
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; CHECK: 5 = MemoryPhi({if.then,2},{phi.3,3})
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; CHECK: 4 = MemoryDef(5)
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; CHECK-NEXT: store i8 4, i8* %local2
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store i8 4, i8* %local2
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br label %phi.1
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phi.1:
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; Order matters here; phi.2 needs to come before phi.3, because that's the order
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; they're visited in.
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; CHECK: 7 = MemoryPhi({phi.2,4},{phi.3,3})
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; CHECK: MemoryUse(1)
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; CHECK-NEXT: load i8, i8* %local
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load i8, i8* %local
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ret void
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}
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; CHECK-LABEL: define void @cross_phi
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define void @cross_phi(i8* noalias %p1, i8* noalias %p2) {
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; CHECK: 1 = MemoryDef(liveOnEntry)
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; CHECK-NEXT: store i8 0, i8* %p1
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store i8 0, i8* %p1
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; CHECK: MemoryUse(1)
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; CHECK-NEXT: load i8, i8* %p1
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load i8, i8* %p1
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br i1 undef, label %a, label %b
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a:
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; CHECK: 2 = MemoryDef(1)
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; CHECK-NEXT: store i8 0, i8* %p2
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store i8 0, i8* %p2
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br i1 undef, label %c, label %d
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b:
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; CHECK: 3 = MemoryDef(1)
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; CHECK-NEXT: store i8 1, i8* %p2
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store i8 1, i8* %p2
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br i1 undef, label %c, label %d
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c:
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; CHECK: 6 = MemoryPhi({a,2},{b,3})
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; CHECK: 4 = MemoryDef(6)
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; CHECK-NEXT: store i8 2, i8* %p2
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store i8 2, i8* %p2
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br label %e
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d:
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; CHECK: 7 = MemoryPhi({a,2},{b,3})
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; CHECK: 5 = MemoryDef(7)
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; CHECK-NEXT: store i8 3, i8* %p2
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store i8 3, i8* %p2
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br label %e
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e:
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; 8 = MemoryPhi({c,4},{d,5})
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; CHECK: MemoryUse(1)
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; CHECK-NEXT: load i8, i8* %p1
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load i8, i8* %p1
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ret void
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}
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; CHECK-LABEL: define void @looped
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define void @looped(i8* noalias %p1, i8* noalias %p2) {
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; CHECK: 1 = MemoryDef(liveOnEntry)
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; CHECK-NEXT: store i8 0, i8* %p1
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store i8 0, i8* %p1
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br label %loop.1
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loop.1:
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; CHECK: 7 = MemoryPhi({%0,1},{loop.3,4})
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; CHECK: 2 = MemoryDef(7)
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; CHECK-NEXT: store i8 0, i8* %p2
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store i8 0, i8* %p2
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br i1 undef, label %loop.2, label %loop.3
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loop.2:
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; CHECK: 6 = MemoryPhi({loop.1,2},{loop.3,4})
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; CHECK: 3 = MemoryDef(6)
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; CHECK-NEXT: store i8 1, i8* %p2
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store i8 1, i8* %p2
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br label %loop.3
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loop.3:
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; CHECK: 5 = MemoryPhi({loop.1,2},{loop.2,3})
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; CHECK: 4 = MemoryDef(5)
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; CHECK-NEXT: store i8 2, i8* %p2
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store i8 2, i8* %p2
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; FIXME: This should be MemoryUse(1)
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; CHECK: MemoryUse(5)
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; CHECK-NEXT: load i8, i8* %p1
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load i8, i8* %p1
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br i1 undef, label %loop.2, label %loop.1
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}
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; CHECK-LABEL: define void @looped_visitedonlyonce
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define void @looped_visitedonlyonce(i8* noalias %p1, i8* noalias %p2) {
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br label %while.cond
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while.cond:
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; CHECK: 5 = MemoryPhi({%0,liveOnEntry},{if.end,3})
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; CHECK-NEXT: br i1 undef, label %if.then, label %if.end
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br i1 undef, label %if.then, label %if.end
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if.then:
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; CHECK: 1 = MemoryDef(5)
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; CHECK-NEXT: store i8 0, i8* %p1
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store i8 0, i8* %p1
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br i1 undef, label %if.end, label %if.then2
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if.then2:
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; CHECK: 2 = MemoryDef(1)
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; CHECK-NEXT: store i8 1, i8* %p2
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store i8 1, i8* %p2
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br label %if.end
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if.end:
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; CHECK: 4 = MemoryPhi({while.cond,5},{if.then,1},{if.then2,2})
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; CHECK: MemoryUse(4)
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; CHECK-NEXT: load i8, i8* %p1
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load i8, i8* %p1
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; CHECK: 3 = MemoryDef(4)
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; CHECK-NEXT: store i8 2, i8* %p2
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store i8 2, i8* %p2
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; CHECK: MemoryUse(4)
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; CHECK-NEXT: load i8, i8* %p1
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load i8, i8* %p1
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br label %while.cond
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}
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