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AliasAnalysis: fix a bug where an index_addr with zero offset can result in a false no-alias result #42339

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Merged
merged 1 commit into from
Apr 13, 2022
Merged

AliasAnalysis: fix a bug where an index_addr with zero offset can result in a false no-alias result #42339

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6 changes: 5 additions & 1 deletion lib/SIL/Utils/Projection.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -389,7 +389,11 @@ Optional<ProjectionPath> ProjectionPath::getProjectionPath(SILValue Start,
Projection AP(Iter);
if (!AP.isValid())
break;
P.Path.push_back(AP);
// We _must_ ignore zero-indexing projections so that alias analysis
// recognizes an "alias" between two addresses where one has such an
// `index_addr 0` instruction and the other doesn't.
if (AP.getKind() != ProjectionKind::Index || AP.getIndex() != 0)
P.Path.push_back(AP);
}
Iter = cast<SingleValueInstruction>(*Iter).getOperand(0);
}
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53 changes: 45 additions & 8 deletions test/SILOptimizer/alias-analysis.sil
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Original file line number Diff line number Diff line change
Expand Up @@ -22,10 +22,10 @@ struct OuterStruct {

// Test overlaping access on a different path; the user has misused an index offset
// CHECK-LABEL: @testOffsetBehindProjection
// CHECK: PAIR #28.
// CHECK: %4 = load %3 : $*Int64
// CHECK: %6 = load %5 : $*Int64
// CHECK: MayAlias
// CHECK: PAIR #23.
// CHECK: %3 = index_addr %1 : $*Int64, %2 : $Builtin.Word
// CHECK: %5 = struct_element_addr %0 : $*MyStruct, #MyStruct.j
// CHECK: NoAlias
sil shared @testOffsetBehindProjection : $@convention(thin) (@inout MyStruct) -> () {
bb0(%0 : $*MyStruct):
%1 = struct_element_addr %0 : $*MyStruct, #MyStruct.i
Expand All @@ -40,10 +40,10 @@ bb0(%0 : $*MyStruct):
}

// CHECK-LABEL: @testOffsetsBehindProjectionOverlap
// CHECK: PAIR #28.
// CHECK: %3 = load %2 : $*Int64
// CHECK: %7 = load %6 : $*Int64
// CHECK: MayAlias
// CHECK: PAIR #21.
// CHECK: %2 = struct_element_addr %1 : $*MyStruct, #MyStruct.i
// CHECK: %6 = struct_element_addr %5 : $*MyStruct, #MyStruct.i
// CHECK: NoAlias
sil shared @testOffsetsBehindProjectionOverlap : $@convention(thin) (@inout OuterStruct) -> () {
bb0(%0 : $*OuterStruct):
%1 = struct_element_addr %0 : $*OuterStruct, #OuterStruct.s
Expand All @@ -58,3 +58,40 @@ bb0(%0 : $*OuterStruct):
%99 = tuple ()
return %99 : $()
}

// CHECK-LABEL: @testIndexOf0
// CHECK: PAIR #8.
// CHECK: %1 = struct_element_addr %0 : $*MyStruct, #MyStruct.i
// CHECK: %3 = index_addr %0 : $*MyStruct, %2 : $Builtin.Word
// CHECK: MayAlias
// CHECK: PAIR #9.
// CHECK: %1 = struct_element_addr %0 : $*MyStruct, #MyStruct.i
// CHECK: %4 = struct_element_addr %3 : $*MyStruct, #MyStruct.i
// CHECK: MustAlias
sil @testIndexOf0 : $@convention(thin) (@inout MyStruct) -> () {
bb0(%0 : $*MyStruct):
%1 = struct_element_addr %0 : $*MyStruct, #MyStruct.i
%2 = integer_literal $Builtin.Word, 0
%3 = index_addr %0 : $*MyStruct, %2 : $Builtin.Word
%4 = struct_element_addr %3 : $*MyStruct, #MyStruct.i
%99 = tuple ()
return %99 : $()
}

// CHECK-LABEL: @testUnknownIndex
// CHECK: PAIR #12.
// CHECK: %2 = struct_element_addr %0 : $*MyStruct, #MyStruct.i
// CHECK: %3 = index_addr %0 : $*MyStruct, %1 : $Builtin.Word
// CHECK: MayAlias
// CHECK: PAIR #13.
// CHECK: %2 = struct_element_addr %0 : $*MyStruct, #MyStruct.i
// CHECK: %4 = struct_element_addr %3 : $*MyStruct, #MyStruct.i
// CHECK: MayAlias
sil @testUnknownIndex : $@convention(thin) (@inout MyStruct, Builtin.Word) -> () {
bb0(%0 : $*MyStruct, %1 : $Builtin.Word):
%2 = struct_element_addr %0 : $*MyStruct, #MyStruct.i
%3 = index_addr %0 : $*MyStruct, %1 : $Builtin.Word
%4 = struct_element_addr %3 : $*MyStruct, #MyStruct.i
%99 = tuple ()
return %99 : $()
}