[flang-commits] [flang] WIP: [flang] AliasAnalysis: Fix pointer component logic (PR #94242)
Joel E. Denny via flang-commits
flang-commits at lists.llvm.org
Mon Jun 3 09:23:26 PDT 2024
https://github.com/jdenny-ornl created https://github.com/llvm/llvm-project/pull/94242
This PR is not yet being proposed for merging. For now, it is intended to facilitate the discussion of an [RFC on Flang AliasAnalysis pointer component logic](https://discourse.llvm.org/t/rfc-rationale-for-flang-aliasanalysis-pointer-component-logic/79252).
>From 484cb901cb3f5ae934b55629bb8537e42d3a832d Mon Sep 17 00:00:00 2001
From: "Joel E. Denny" <jdenny.ornl at gmail.com>
Date: Tue, 28 May 2024 19:14:22 -0400
Subject: [PATCH 1/2] WIP: [flang] AliasAnalysis: Fix pointer component logic
---
.../lib/Optimizer/Analysis/AliasAnalysis.cpp | 30 ++++++++++++-------
.../AliasAnalysis/alias-analysis-3.fir | 19 ++++++------
.../AliasAnalysis/alias-analysis-9.fir | 12 ++++----
3 files changed, 34 insertions(+), 27 deletions(-)
diff --git a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
index 9d0d706a85c5e..571b78dc64aa5 100644
--- a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
+++ b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
@@ -122,6 +122,18 @@ AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
}
if (lhsSrc.kind == rhsSrc.kind) {
+ // If the kinds and origins are the same, then lhs and rhs must alias unless
+ // either source is approximate. Approximate sources are for parts of the
+ // origin, but we don't have info here on which parts and whether they
+ // overlap, so we normally return MayAlias in that case.
+ //
+ // There is an exceptional case: The origins might compare unequal because
+ // only one has !isData(). If that source is approximate and the other is
+ // not, then the former is the source for the address *of* a pointer
+ // component in a composite, and the latter is for the address of that
+ // composite. As for the address of any composite vs. the address of one of
+ // its components, a store to one can affect a load from the other, so the
+ // result is MayAlias.
if (lhsSrc.origin == rhsSrc.origin) {
LLVM_DEBUG(llvm::dbgs()
<< " aliasing because same source kind and origin\n");
@@ -129,6 +141,13 @@ AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
return AliasResult::MayAlias;
return AliasResult::MustAlias;
}
+ if (lhsSrc.origin.u == rhsSrc.origin.u &&
+ ((lhsSrc.approximateSource && !lhsSrc.isData() && !rhsSrc.approximateSource) ||
+ (rhsSrc.approximateSource && !rhsSrc.isData() && !lhsSrc.approximateSource))) {
+ LLVM_DEBUG(llvm::dbgs()
+ << " aliasing between composite and pointer component\n");
+ return AliasResult::MayAlias;
+ }
// Two host associated accesses may overlap due to an equivalence.
if (lhsSrc.kind == SourceKind::HostAssoc) {
@@ -173,17 +192,6 @@ AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
return AliasResult::MayAlias;
}
- // Box for POINTER component inside an object of a derived type
- // may alias box of a POINTER object, as well as boxes for POINTER
- // components inside two objects of derived types may alias.
- if ((src1->isRecordWithPointerComponent() && src2->isTargetOrPointer()) ||
- (src2->isRecordWithPointerComponent() && src1->isTargetOrPointer()) ||
- (src1->isRecordWithPointerComponent() &&
- src2->isRecordWithPointerComponent())) {
- LLVM_DEBUG(llvm::dbgs() << " aliasing because of pointer components\n");
- return AliasResult::MayAlias;
- }
-
return AliasResult::NoAlias;
}
diff --git a/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir b/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir
index 91829a461dc72..2bf326f2d2af2 100644
--- a/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir
+++ b/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir
@@ -16,12 +16,12 @@
// end subroutine test
// end module m
-// A composite with a pointer component may alias with a dummy pointer
+// A composite with a pointer component does not alias with a dummy pointer
// CHECK-LABEL: Testing : "_QMmPtest
-// CHECK: a#0 <-> func.region0#0: MayAlias
+// CHECK: a#0 <-> func.region0#0: NoAlias
-// FIXME: a's box cannot alias with raw reference to f32 (x), so MayAlias below must be NoAlias:
-// CHECK: a#0 <-> func.region0#1: MayAlias
+// a's box cannot alias with raw reference to f32 (x)
+// CHECK: a#0 <-> func.region0#1: NoAlias
// pointer_dummy's box cannot alias with raw reference to f32 (x)
// CHECK: func.region0#0 <-> func.region0#1: NoAlias
@@ -46,7 +46,7 @@ func.func private @_QPtest2(!fir.ref<f32>)
// -----
-// A composite with a pointer component may alias with a dummy
+// A composite with a pointer component does not alias with a dummy
// argument of composite type with a pointer component:
// module m
// type t
@@ -63,7 +63,7 @@ func.func private @_QPtest2(!fir.ref<f32>)
// end module m
// CHECK-LABEL: Testing : "_QMmPtest"
-// CHECK: a#0 <-> func.region0#0: MayAlias
+// CHECK: a#0 <-> func.region0#0: NoAlias
fir.global @_QMmEa : !fir.type<_QMmTt{pointer_component:!fir.box<!fir.ptr<f32>>}> {
%0 = fir.undefined !fir.type<_QMmTt{pointer_component:!fir.box<!fir.ptr<f32>>}>
@@ -88,7 +88,7 @@ func.func private @_QPtest2(!fir.ref<f32>)
// -----
// Two dummy arguments of composite type with a pointer component
-// may alias each other:
+// do not alias each other:
// module m
// type t
// real, pointer :: pointer_component
@@ -103,7 +103,7 @@ func.func private @_QPtest2(!fir.ref<f32>)
// end module m
// CHECK-LABEL: Testing : "_QMmPtest"
-// CHECK: func.region0#0 <-> func.region0#1: MayAlias
+// CHECK: func.region0#0 <-> func.region0#1: NoAlias
func.func @_QMmPtest(%arg0: !fir.ref<!fir.type<_QMmTt{pointer_component:!fir.box<!fir.ptr<f32>>}>> {fir.bindc_name = "a"}, %arg1: !fir.ref<!fir.type<_QMmTt{pointer_component:!fir.box<!fir.ptr<f32>>}>> {fir.bindc_name = "b"}, %arg2: !fir.ref<f32> {fir.bindc_name = "x", fir.target}) attributes {test.ptr = "func"} {
%0 = fir.field_index pointer_component, !fir.type<_QMmTt{pointer_component:!fir.box<!fir.ptr<f32>>}>
@@ -137,8 +137,7 @@ func.func private @_QPtest2(!fir.ref<f32>)
// end module m
// CHECK-LABEL: Testing : "_QMmPtest"
-// FIXME: MayAlias must be NoAlias
-// CHECK: func.region0#0 <-> func.region0#1: MayAlias
+// CHECK: func.region0#0 <-> func.region0#1: NoAlias
func.func @_QMmPtest(%arg0: !fir.ref<!fir.type<_QMmTt{allocatable_component:!fir.box<!fir.heap<f32>>}>> {fir.bindc_name = "a"}, %arg1: !fir.ref<!fir.type<_QMmTt{allocatable_component:!fir.box<!fir.heap<f32>>}>> {fir.bindc_name = "b"}) attributes {test.ptr = "func"} {
%0 = fir.field_index allocatable_component, !fir.type<_QMmTt{allocatable_component:!fir.box<!fir.heap<f32>>}>
diff --git a/flang/test/Analysis/AliasAnalysis/alias-analysis-9.fir b/flang/test/Analysis/AliasAnalysis/alias-analysis-9.fir
index df24a6d32aa59..67ea4d20caa60 100644
--- a/flang/test/Analysis/AliasAnalysis/alias-analysis-9.fir
+++ b/flang/test/Analysis/AliasAnalysis/alias-analysis-9.fir
@@ -17,13 +17,13 @@
// end module
// CHECK-LABEL: Testing : "_QMmPfoo"
-// TODO: x and y are non pointer, non target argument and therefore do not alias.
-// CHECK-DAG: x#0 <-> y#0: MayAlias
+// x and y are non pointer, non target argument and therefore do not alias.
+// CHECK-DAG: x#0 <-> y#0: NoAlias
-// TODO: y is not a pointer object and therefore does not alias with the x%next component.
-// Also assigning x to y would not modify x.next
-// CHECK-DAG: y#0 <-> xnext1#0: MayAlias
-// CHECK-DAG: y#0 <-> xnext2#0: MayAlias
+// y is not a pointer object and therefore does not alias with the x%next
+// component. Also assigning x to y would not modify x.next
+// CHECK-DAG: y#0 <-> xnext1#0: NoAlias
+// CHECK-DAG: y#0 <-> xnext2#0: NoAlias
// We need to catch the fact that assigning y to x will modify xnext.
// The only side-effect between the 2 loads of x.next is the assignment to x,
>From 9f6d2a7add52dcd3fe51d7376be91b1f3e9b7646 Mon Sep 17 00:00:00 2001
From: "Joel E. Denny" <jdenny.ornl at gmail.com>
Date: Thu, 30 May 2024 15:09:54 -0400
Subject: [PATCH 2/2] WIP: Fix case of ptr dummy arg vs. ptr component
---
.../lib/Optimizer/Analysis/AliasAnalysis.cpp | 41 ++++++++++++++++++-
.../AliasAnalysis/alias-analysis-3.fir | 4 +-
2 files changed, 41 insertions(+), 4 deletions(-)
diff --git a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
index 571b78dc64aa5..9d6640bf181ec 100644
--- a/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
+++ b/flang/lib/Optimizer/Analysis/AliasAnalysis.cpp
@@ -145,7 +145,7 @@ AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
((lhsSrc.approximateSource && !lhsSrc.isData() && !rhsSrc.approximateSource) ||
(rhsSrc.approximateSource && !rhsSrc.isData() && !lhsSrc.approximateSource))) {
LLVM_DEBUG(llvm::dbgs()
- << " aliasing between composite and pointer component\n");
+ << " aliasing between composite and non-data component\n");
return AliasResult::MayAlias;
}
@@ -185,13 +185,50 @@ AliasResult AliasAnalysis::alias(Value lhs, Value rhs) {
src2->attributes.set(Attribute::Target);
}
- // Dummy TARGET/POINTER argument may alias with a global TARGET/POINTER.
+ // Two TARGET/POINTERs may alias.
if (src1->isTargetOrPointer() && src2->isTargetOrPointer() &&
src1->isData() == src2->isData()) {
LLVM_DEBUG(llvm::dbgs() << " aliasing because of target or pointer\n");
return AliasResult::MayAlias;
}
+ // A pointer dummy arg may alias a global composite with a pointer component.
+ //
+ // module m
+ // type t
+ // real, pointer :: p
+ // end type
+ // type(t) :: a
+ // type(t) :: b
+ // contains
+ // subroutine test(p)
+ // real, pointer :: p
+ // p = 42
+ // a = b
+ // print *, p
+ // end subroutine
+ // end module
+ // program
+ // use m
+ // real, target :: x1 = 1
+ // real, target :: x2 = 2
+ // a%p => x1
+ // b%p => x2
+ // call test(a%p)
+ // end
+ //
+ // The dummy argument p is an alias for a%p, even for the purposes of pointer
+ // association during the assignment a = b. Thus, the program should print 2.
+ if (src1->kind == SourceKind::Global &&
+ src1->isRecordWithPointerComponent() &&
+ src2->kind == SourceKind::Argument &&
+ src2->attributes.test(Attribute::Pointer)) {
+ LLVM_DEBUG(llvm::dbgs()
+ << " aliasing because of pointer arg and global composite with "
+ << "pointer component\n");
+ return AliasResult::MayAlias;
+ }
+
return AliasResult::NoAlias;
}
diff --git a/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir b/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir
index 2bf326f2d2af2..eab438576c2bc 100644
--- a/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir
+++ b/flang/test/Analysis/AliasAnalysis/alias-analysis-3.fir
@@ -16,9 +16,9 @@
// end subroutine test
// end module m
-// A composite with a pointer component does not alias with a dummy pointer
+// A composite with a pointer component may alias with a dummy pointer
// CHECK-LABEL: Testing : "_QMmPtest
-// CHECK: a#0 <-> func.region0#0: NoAlias
+// CHECK: a#0 <-> func.region0#0: MayAlias
// a's box cannot alias with raw reference to f32 (x)
// CHECK: a#0 <-> func.region0#1: NoAlias
More information about the flang-commits
mailing list