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clang-p2996/llvm/test/Analysis/BasicAA/phi-aa.ll
Nikita Popov 8b1c4e310c [BasicAA] Handle two unknown sizes for GEPs 
If we have two unknown sizes and one GEP operand and one non-GEP
operand, then we currently simply return MayAlias. The comment says
we can't do anything useful ... but we can! We can still check that
the underlying objects are different (and do so for the GEP-GEP case).

To reduce the compile-time impact, this a) checks this early, before
doing the relatively expensive GEP decomposition that will not be
used and b) doesn't do the check if the other operand is a phi or
select. In that case, the phi/select will already recurse, so this
would just do two slightly different recursive walks that arrive at
the same roots.

Compile-time is still a bit of a mixed bag: https://llvm-compile-time-tracker.com/compare.php?from=624af932a808b363a888139beca49f57313d9a3b&to=845356e14adbe651a553ed11318ddb5e79a24bcd&stat=instructions
On average this is a small improvement, but sqlite with ThinLTO has
a 0.5% regression (lencod has a 1% improvement).

The BasicAA test case checks this by using two memsets with unknown
size. However, the more interesting case where this is useful is
the LoopVectorize test case, as analysis of accesses in loops tends
to always us unknown sizes.

Differential Revision: https://reviews.llvm.org/D92401
2020-12-11 18:45:53 +01:00

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; RUN: opt < %s -phi-values -basic-aa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
; RUN: opt < %s -aa-pipeline=basic-aa -passes='require<phi-values>,aa-eval' -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
; rdar://7282591
@X = common global i32 0
@Y = common global i32 0
@Z = common global i32 0
; CHECK-LABEL: foo
; CHECK: NoAlias: i32* %P, i32* @Z
define void @foo(i32 %cond) nounwind {
entry:
%"alloca point" = bitcast i32 0 to i32
%tmp = icmp ne i32 %cond, 0
br i1 %tmp, label %bb, label %bb1
bb:
br label %bb2
bb1:
br label %bb2
bb2:
%P = phi i32* [ @X, %bb ], [ @Y, %bb1 ]
%tmp1 = load i32, i32* @Z, align 4
store i32 123, i32* %P, align 4
%tmp2 = load i32, i32* @Z, align 4
br label %return
return:
ret void
}
; Pointers can vary in between iterations of loops.
; PR18068
; CHECK-LABEL: pr18068
; CHECK: MayAlias: i32* %0, i32* %arrayidx5
; CHECK: NoAlias: i32* %arrayidx13, i32* %arrayidx5
define i32 @pr18068(i32* %jj7, i32* %j) {
entry:
%oa5 = alloca [100 x i32], align 16
br label %codeRepl
codeRepl:
%0 = phi i32* [ %arrayidx13, %for.body ], [ %j, %entry ]
%targetBlock = call i1 @cond(i32* %jj7)
br i1 %targetBlock, label %for.body, label %bye
for.body:
%1 = load i32, i32* %jj7, align 4
%idxprom4 = zext i32 %1 to i64
%arrayidx5 = getelementptr inbounds [100 x i32], [100 x i32]* %oa5, i64 0, i64 %idxprom4
%2 = load i32, i32* %arrayidx5, align 4
%sub6 = sub i32 %2, 6
store i32 %sub6, i32* %arrayidx5, align 4
; %0 and %arrayidx5 can alias! It is not safe to DSE the above store.
%3 = load i32, i32* %0, align 4
store i32 %3, i32* %arrayidx5, align 4
%sub11 = add i32 %1, -1
%idxprom12 = zext i32 %sub11 to i64
%arrayidx13 = getelementptr inbounds [100 x i32], [100 x i32]* %oa5, i64 0, i64 %idxprom12
call void @inc(i32* %jj7)
br label %codeRepl
bye:
%.reload = load i32, i32* %jj7, align 4
ret i32 %.reload
}
declare i1 @cond(i32*)
declare void @inc(i32*)
; When we have a chain of phis in nested loops we should recognise if there's
; actually only one underlying value.
; CHECK-LABEL: loop_phi_chain
; CHECK: NoAlias: i32* %val1, i32* @Y
; CHECK: NoAlias: i32* %val2, i32* @Y
; CHECK: NoAlias: i32* %val3, i32* @Y
define void @loop_phi_chain(i32 %a, i32 %b, i32 %c) {
entry:
br label %loop1
loop1:
%n1 = phi i32 [ 0, %entry ], [ %add1, %loop2 ]
%val1 = phi i32* [ @X, %entry ], [ %val2, %loop2 ]
%add1 = add i32 %n1, 1
%cmp1 = icmp ne i32 %n1, 32
br i1 %cmp1, label %loop2, label %end
loop2:
%n2 = phi i32 [ 0, %loop1 ], [ %add2, %loop3 ]
%val2 = phi i32* [ %val1, %loop1 ], [ %val3, %loop3 ]
%add2 = add i32 %n2, 1
%cmp2 = icmp ne i32 %n2, 32
br i1 %cmp2, label %loop3, label %loop1
loop3:
%n3 = phi i32 [ 0, %loop2 ], [ %add3, %loop3 ]
%val3 = phi i32* [ %val2, %loop2 ], [ %val3, %loop3 ]
store i32 0, i32* %val3, align 4
store i32 0, i32* @Y, align 4
%add3 = add i32 %n3, 1
%cmp3 = icmp ne i32 %n3, 32
br i1 %cmp3, label %loop3, label %loop2
end:
ret void
}
; CHECK-LABEL: phi_and_select
; CHECK: MustAlias: i32* %p, i32* %s
define void @phi_and_select(i1 %c, i1 %c2, i32* %x, i32* %y) {
entry:
br i1 %c, label %true, label %false
true:
br label %exit
false:
br label %exit
exit:
%p = phi i32* [ %x, %true ], [ %y, %false ]
%s = select i1 %c2, i32* %p, i32* %p
store i32 0, i32* %p
store i32 0, i32* %s
ret void
}
; CHECK-LABEL: phi_and_phi_cycle
; CHECK: NoAlias: i32* %p1, i32* %p2
define void @phi_and_phi_cycle(i32* noalias %x, i32* noalias %y) {
entry:
br label %loop
loop:
%p1 = phi i32* [ %x, %entry ], [ %p1.next, %loop ]
%p2 = phi i32* [ %y, %entry ], [ %p2.next, %loop ]
%p1.next = getelementptr i32, i32* %p1, i64 1
%p2.next = getelementptr i32, i32* %p1, i64 2
store i32 0, i32* %p1
store i32 0, i32* %p2
br label %loop
}
; CHECK-LABEL: phi_and_gep_unknown_size
; CHECK: NoModRef: call void @llvm.memset.p0i8.i32(i8* %g, i8 0, i32 %size, i1 false) <-> call void @llvm.memset.p0i8.i32(i8* %z, i8 0, i32 %size, i1 false)
define void @phi_and_gep_unknown_size(i1 %c, i8* %x, i8* %y, i8* noalias %z, i32 %size) {
entry:
br i1 %c, label %true, label %false
true:
br label %exit
false:
br label %exit
exit:
%p = phi i8* [ %x, %true ], [ %y, %false ]
%g = getelementptr inbounds i8, i8* %p, i64 1
call void @llvm.memset.p0i8.i32(i8* %g, i8 0, i32 %size, i1 false)
call void @llvm.memset.p0i8.i32(i8* %z, i8 0, i32 %size, i1 false)
ret void
}
declare void @llvm.memset.p0i8.i32(i8*, i8, i32, i1)
; CHECK-LABEL: unsound_inequality
; CHECK: MayAlias: i32* %arrayidx13, i32* %phi
; CHECK: MayAlias: i32* %arrayidx5, i32* %phi
; CHECK: NoAlias: i32* %arrayidx13, i32* %arrayidx5
; When recursively reasoning about phis, we can't use predicates between
; two values as we might be comparing the two from different iterations.
define i32 @unsound_inequality(i32* %jj7, i32* %j) {
entry:
%oa5 = alloca [100 x i32], align 16
br label %for.body
for.body: ; preds = %for.body, %entry
%phi = phi i32* [ %arrayidx13, %for.body ], [ %j, %entry ]
%idx = load i32, i32* %jj7, align 4
%arrayidx5 = getelementptr inbounds [100 x i32], [100 x i32]* %oa5, i64 0, i32 %idx
store i32 0, i32* %arrayidx5, align 4
store i32 0, i32* %phi, align 4
%notequal = add i32 %idx, 1
%arrayidx13 = getelementptr inbounds [100 x i32], [100 x i32]* %oa5, i64 0, i32 %notequal
store i32 0, i32* %arrayidx13, align 4
br label %for.body
}
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