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llvm-mirror/test/Analysis/BasicAA/phi-aa.ll
Nikita Popov 9fa93a3e70 [BasicAA] Always strip single-argument phi nodes 
We can always look through single-argument (LCSSA) phi nodes when
performing alias analysis. getUnderlyingObject() already does this,
but stripPointerCastsAndInvariantGroups() does not. We still look
through these phi nodes with the usual aliasPhi() logic, but
sometimes get sub-optimal results due to the restrictions on value
equivalence when looking through arbitrary phi nodes. I think it's
generally beneficial to keep the underlying object logic and the
pointer cast stripping logic in sync, insofar as it is possible.

With this patch we get marginally better results:

  aa.NumMayAlias | 5010069 | 5009861
  aa.NumMustAlias | 347518 | 347674
  aa.NumNoAlias | 27201336 | 27201528
  ...
  licm.NumPromoted | 1293 | 1296

I've renamed the relevant strip method to stripPointerCastsForAliasAnalysis(),
as we're past the point where we can explicitly spell out everything
that's getting stripped.

Differential Revision: https://reviews.llvm.org/D96668
2021-02-18 23:07:50 +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: Just Mod: 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)
; TODO: This should be NoModRef.
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
}
; CHECK-LABEL: single_arg_phi
; CHECK: NoAlias: i32* %ptr, i32* %ptr.next
; CHECK: MustAlias: i32* %ptr, i32* %ptr.phi
; CHECK: MustAlias: i32* %ptr.next, i32* %ptr.next.phi
define void @single_arg_phi(i32* %ptr.base) {
entry:
br label %loop
loop:
%ptr = phi i32* [ %ptr.base, %entry ], [ %ptr.next, %split ]
%ptr.next = getelementptr inbounds i32, i32* %ptr, i64 1
br label %split
split:
%ptr.phi = phi i32* [ %ptr, %loop ]
%ptr.next.phi = phi i32* [ %ptr.next, %loop ]
br label %loop
}
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