[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

llvm-svn: 369786

1 files changed, 149 insertions, 0 deletions

diff --git a/llvm/test/Analysis/BasicAA/dereferenceable.ll b/llvm/test/Analysis/BasicAA/dereferenceable.ll
new file mode 100644
index 00000000000..efc9addbee1
--- /dev/null
+++ b/llvm/test/Analysis/BasicAA/dereferenceable.ll
@@ -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"
+
+@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
+}