[llvm] r369786 - [BasicAA] Use dereferenceability to reason about aliasing
Johannes Doerfert via llvm-commits
llvm-commits at lists.llvm.org
Fri Aug 23 10:56:10 PDT 2019
Author: jdoerfert
Date: Fri Aug 23 10:56:10 2019
New Revision: 369786
URL: http://llvm.org/viewvc/llvm-project?rev=369786&view=rev
Log:
[BasicAA] Use dereferenceability to reason about aliasing
Summary:
We already use the fact that an object with known size X does not alias
another objection of size Y > X before. With this commit, we use
dereferenceability information to determine a lower bound for Y and not
only rely on the user provided query size.
The result for @global_and_deref_arg_2() and @local_and_deref_ret_2()
in test/Analysis/BasicAA/dereferenceable.ll improved with this patch.
Reviewers: asbirlea, chandlerc, hfinkel, sanjoy
Subscribers: hiraditya, bollu, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66157
Added:
llvm/trunk/test/Analysis/BasicAA/dereferenceable.ll
Modified:
llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=369786&r1=369785&r2=369786&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Fri Aug 23 10:56:10 2019
@@ -233,6 +233,26 @@ static bool isObjectSmallerThan(const Va
return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size;
}
+/// Return the minimal extent from \p V to the end of the underlying object,
+/// assuming the result is used in an aliasing query. E.g., we do use the query
+/// location size and the fact that null pointers cannot alias here.
+static uint64_t getMinimalExtentFrom(const Value &V,
+ const LocationSize &LocSize,
+ const DataLayout &DL,
+ bool NullIsValidLoc) {
+ // If we have dereferenceability information we know a lower bound for the
+ // extent as accesses for a lower offset would be valid. We need to exclude
+ // the "or null" part if null is a valid pointer.
+ bool CanBeNull;
+ uint64_t DerefBytes = V.getPointerDereferenceableBytes(DL, CanBeNull);
+ DerefBytes = (CanBeNull && NullIsValidLoc) ? 0 : DerefBytes;
+ // If queried with a precise location size, we assume that location size to be
+ // accessed, thus valid.
+ if (LocSize.isPrecise())
+ DerefBytes = std::max(DerefBytes, LocSize.getValue());
+ return DerefBytes;
+}
+
/// Returns true if we can prove that the object specified by V has size Size.
static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
const TargetLibraryInfo &TLI, bool NullIsValidLoc) {
@@ -1792,10 +1812,12 @@ AliasResult BasicAAResult::aliasCheck(co
// If the size of one access is larger than the entire object on the other
// side, then we know such behavior is undefined and can assume no alias.
bool NullIsValidLocation = NullPointerIsDefined(&F);
- if ((V1Size.isPrecise() && isObjectSmallerThan(O2, V1Size.getValue(), DL, TLI,
- NullIsValidLocation)) ||
- (V2Size.isPrecise() && isObjectSmallerThan(O1, V2Size.getValue(), DL, TLI,
- NullIsValidLocation)))
+ if ((isObjectSmallerThan(
+ O2, getMinimalExtentFrom(*V1, V1Size, DL, NullIsValidLocation), DL,
+ TLI, NullIsValidLocation)) ||
+ (isObjectSmallerThan(
+ O1, getMinimalExtentFrom(*V2, V2Size, DL, NullIsValidLocation), DL,
+ TLI, NullIsValidLocation)))
return NoAlias;
// Check the cache before climbing up use-def chains. This also terminates
Added: llvm/trunk/test/Analysis/BasicAA/dereferenceable.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/BasicAA/dereferenceable.ll?rev=369786&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/BasicAA/dereferenceable.ll (added)
+++ llvm/trunk/test/Analysis/BasicAA/dereferenceable.ll Fri Aug 23 10:56:10 2019
@@ -0,0 +1,149 @@
+; RUN: opt -basicaa -print-all-alias-modref-info -aa-eval -analyze < %s 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+ at G = global i32 0, align 4
+
+define i64 @global_and_deref_arg_1(i64* dereferenceable(8) %arg) {
+; CHECK: Function: global_and_deref_arg_1: 2 pointers, 0 call sites
+; CHECK-NEXT: NoAlias: i32* @G, i64* %arg
+bb:
+ store i64 1, i64* %arg, align 8
+ store i32 0, i32* @G, align 4
+ %tmp = load i64, i64* %arg, align 8
+ ret i64 %tmp
+}
+
+define i32 @global_and_deref_arg_2(i32* dereferenceable(8) %arg) {
+; CHECK: Function: global_and_deref_arg_2: 2 pointers, 0 call sites
+; CHECK-NEXT: NoAlias: i32* %arg, i32* @G
+bb:
+ store i32 1, i32* %arg, align 8
+ store i32 0, i32* @G, align 4
+ %tmp = load i32, i32* %arg, align 8
+ ret i32 %tmp
+}
+
+define i32 @byval_and_deref_arg_1(i32* byval %obj, i64* dereferenceable(8) %arg) {
+; CHECK: Function: byval_and_deref_arg_1: 2 pointers, 0 call sites
+; CHECK-NEXT: NoAlias: i32* %obj, i64* %arg
+bb:
+ store i32 1, i32* %obj, align 4
+ store i64 0, i64* %arg, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
+
+define i32 @byval_and_deref_arg_2(i32* byval %obj, i32* dereferenceable(8) %arg) {
+; CHECK: Function: byval_and_deref_arg_2: 2 pointers, 0 call sites
+; CHECK-NEXT: NoAlias: i32* %arg, i32* %obj
+bb:
+ store i32 1, i32* %obj, align 4
+ store i32 0, i32* %arg, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
+
+declare dereferenceable(8) i32* @get_i32_deref8()
+declare dereferenceable(8) i64* @get_i64_deref8()
+declare void @unknown(i32*)
+
+define i32 @local_and_deref_ret_1() {
+; CHECK: Function: local_and_deref_ret_1: 2 pointers, 2 call sites
+; CHECK-NEXT: NoAlias: i32* %obj, i64* %ret
+bb:
+ %obj = alloca i32
+ call void @unknown(i32* %obj)
+ %ret = call dereferenceable(8) i64* @get_i64_deref8()
+ store i32 1, i32* %obj, align 4
+ store i64 0, i64* %ret, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
+
+define i32 @local_and_deref_ret_2() {
+; CHECK: Function: local_and_deref_ret_2: 2 pointers, 2 call sites
+; CHECK-NEXT: NoAlias: i32* %obj, i32* %ret
+bb:
+ %obj = alloca i32
+ call void @unknown(i32* %obj)
+ %ret = call dereferenceable(8) i32* @get_i32_deref8()
+ store i32 1, i32* %obj, align 4
+ store i32 0, i32* %ret, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
+
+
+; Baseline tests, same as above but with 2 instead of 8 dereferenceable bytes.
+
+define i64 @global_and_deref_arg_non_deref_1(i64* dereferenceable(2) %arg) {
+; CHECK: Function: global_and_deref_arg_non_deref_1: 2 pointers, 0 call sites
+; CHECK-NEXT: NoAlias: i32* @G, i64* %arg
+bb:
+ store i64 1, i64* %arg, align 8
+ store i32 0, i32* @G, align 4
+ %tmp = load i64, i64* %arg, align 8
+ ret i64 %tmp
+}
+
+define i32 @global_and_deref_arg_non_deref_2(i32* dereferenceable(2) %arg) {
+; CHECK: Function: global_and_deref_arg_non_deref_2: 2 pointers, 0 call sites
+; Different result than above (see @global_and_deref_arg_2).
+; CHECK-NEXT: MayAlias: i32* %arg, i32* @G
+bb:
+ store i32 1, i32* %arg, align 8
+ store i32 0, i32* @G, align 4
+ %tmp = load i32, i32* %arg, align 8
+ ret i32 %tmp
+}
+
+define i32 @byval_and_deref_arg_non_deref_1(i32* byval %obj, i64* dereferenceable(2) %arg) {
+; CHECK: Function: byval_and_deref_arg_non_deref_1: 2 pointers, 0 call sites
+; CHECK-NEXT: NoAlias: i32* %obj, i64* %arg
+bb:
+ store i32 1, i32* %obj, align 4
+ store i64 0, i64* %arg, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
+
+define i32 @byval_and_deref_arg_non_deref_2(i32* byval %obj, i32* dereferenceable(2) %arg) {
+; CHECK: Function: byval_and_deref_arg_non_deref_2: 2 pointers, 0 call sites
+; CHECK-NEXT: NoAlias: i32* %arg, i32* %obj
+bb:
+ store i32 1, i32* %obj, align 4
+ store i32 0, i32* %arg, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
+
+declare dereferenceable(2) i32* @get_i32_deref2()
+declare dereferenceable(2) i64* @get_i64_deref2()
+
+define i32 @local_and_deref_ret_non_deref_1() {
+; CHECK: Function: local_and_deref_ret_non_deref_1: 2 pointers, 2 call sites
+; CHECK-NEXT: NoAlias: i32* %obj, i64* %ret
+bb:
+ %obj = alloca i32
+ call void @unknown(i32* %obj)
+ %ret = call dereferenceable(2) i64* @get_i64_deref2()
+ store i32 1, i32* %obj, align 4
+ store i64 0, i64* %ret, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
+
+define i32 @local_and_deref_ret_non_deref_2() {
+; CHECK: Function: local_and_deref_ret_non_deref_2: 2 pointers, 2 call sites
+; Different result than above (see @local_and_deref_ret_2).
+; CHECK-NEXT: MayAlias: i32* %obj, i32* %ret
+bb:
+ %obj = alloca i32
+ call void @unknown(i32* %obj)
+ %ret = call dereferenceable(2) i32* @get_i32_deref2()
+ store i32 1, i32* %obj, align 4
+ store i32 0, i32* %ret, align 8
+ %tmp = load i32, i32* %obj, align 4
+ ret i32 %tmp
+}
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