fhahn updated this revision to Diff 291183.
fhahn marked an inline comment as done.
fhahn added a comment.
Add check lines for escape examples. Note that for return-by-value we already
add noalias to the pointer unconditionally.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D85473/new/
https://reviews.llvm.org/D85473
Files:
clang/include/clang/Basic/CodeGenOptions.def
clang/include/clang/Driver/Options.td
clang/lib/CodeGen/CGCall.cpp
clang/lib/Frontend/CompilerInvocation.cpp
clang/test/CodeGen/pass-by-value-noalias.c
clang/test/CodeGenCXX/pass-by-value-noalias.cpp
clang/test/CodeGenObjC/pass-by-value-noalias.m
Index: clang/test/CodeGenObjC/pass-by-value-noalias.m
===================================================================
--- /dev/null
+++ clang/test/CodeGenObjC/pass-by-value-noalias.m
@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns -fobjc-runtime-has-weak -fobjc-arc -fobjc-dispatch-method=mixed %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
+// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns -fobjc-runtime-has-weak -fobjc-arc -fobjc-dispatch-method=mixed %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
+
+@interface Bar
+@property char value;
+@end
+
+// A struct large enough so it is not passed in registers on ARM64, but with a
+// weak reference, so noalias should not be added even with
+// -fpass-by-value-is-noalias.
+struct Foo {
+ int a;
+ int b;
+ int c;
+ int d;
+ int e;
+ Bar *__weak f;
+};
+
+// WITH_NOALIAS: define void @take(%struct.Foo* %arg)
+// NO_NOALIAS: define void @take(%struct.Foo* %arg)
+void take(struct Foo arg) {}
Index: clang/test/CodeGenCXX/pass-by-value-noalias.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/pass-by-value-noalias.cpp
@@ -0,0 +1,73 @@
+// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
+// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
+
+// A trivial struct large enough so it is not passed in registers on ARM64.
+struct Foo {
+ int a;
+ int b;
+ int c;
+ int d;
+ int e;
+ int f;
+};
+
+// Make sure noalias is added to indirect arguments with trivially copyable types
+// if -fpass-by-value-is-noalias is provided.
+
+// WITH_NOALIAS: define void @_Z4take3Foo(%struct.Foo* noalias %arg)
+// NO_NOALIAS: define void @_Z4take3Foo(%struct.Foo* %arg)
+void take(Foo arg) {}
+
+int G;
+
+// NonTrivial is not trivially-copyable, because it has a non-trivial copy
+// constructor.
+struct NonTrivial {
+ int a;
+ int b;
+ int c;
+ int d;
+ int e;
+ int f;
+
+ NonTrivial(const NonTrivial &Other) {
+ a = G + 10 + Other.a;
+ }
+};
+
+// Make sure noalias is not added to indirect arguments that are not trivially
+// copyable even if -fpass-by-value-is-noalias is provided.
+
+// WITH_NOALIAS: define void @_Z4take10NonTrivial(%struct.NonTrivial* %arg)
+// NO_NOALIAS: define void @_Z4take10NonTrivial(%struct.NonTrivial* %arg)
+void take(NonTrivial arg) {}
+
+// Escape examples. Pointers to the objects passed to take() may escape, depending on whether a temporary copy is created or not (e.g. due to NRVO).
+struct A {
+ A(A **where) : data{"hello world 1"} {
+ *where = this; //Escaped pointer 1 (proposed UB?)
+ }
+
+ A() : data{"hello world 2"} {}
+
+ char data[32];
+};
+A *p;
+
+// WITH_NOALIAS: define void @_Z4take1A(%struct.A* noalias %arg)
+// NO_NOALIAS: define void @_Z4take1A(%struct.A* %arg)
+void take(A arg) {}
+
+// WITH_NOALIAS: define void @_Z7CreateAPP1A(%struct.A* noalias sret align 1 %agg.result, %struct.A** %where)
+// NO_NOALIAS: define void @_Z7CreateAPP1A(%struct.A* noalias sret align 1 %agg.result, %struct.A** %where)
+A CreateA(A **where) {
+ A justlikethis;
+ *where = &justlikethis; //Escaped pointer 2 (should also be UB, then)
+ return justlikethis;
+}
+
+// elsewhere, perhaps compiled by a smarter compiler that doesn't make a copy here
+void test() {
+ take({&p}); // 1
+ take(CreateA(&p)); // 2
+}
Index: clang/test/CodeGen/pass-by-value-noalias.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/pass-by-value-noalias.c
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fpass-by-value-is-noalias -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=WITH_NOALIAS %s
+// RUN: %clang_cc1 -triple arm64-apple-iphoneos -emit-llvm -disable-llvm-optzns %s -o - 2>&1 | FileCheck --check-prefix=NO_NOALIAS %s
+
+// A struct large enough so it is not passed in registers on ARM64.
+struct Foo {
+ int a;
+ int b;
+ int c;
+ int d;
+ int e;
+ int f;
+};
+
+// WITH_NOALIAS: define void @take(%struct.Foo* noalias %arg)
+// NO_NOALIAS: define void @take(%struct.Foo* %arg)
+void take(struct Foo arg) {}
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -1453,6 +1453,8 @@
std::string(Args.getLastArgValue(OPT_fsymbol_partition_EQ));
Opts.ForceAAPCSBitfieldLoad = Args.hasArg(OPT_ForceAAPCSBitfieldLoad);
+
+ Opts.PassByValueIsNoAlias = Args.hasArg(OPT_fpass_by_value_is_noalias);
return Success;
}
Index: clang/lib/CodeGen/CGCall.cpp
===================================================================
--- clang/lib/CodeGen/CGCall.cpp
+++ clang/lib/CodeGen/CGCall.cpp
@@ -2201,6 +2201,13 @@
if (AI.getIndirectByVal())
Attrs.addByValAttr(getTypes().ConvertTypeForMem(ParamType));
+ auto *Decl = ParamType->getAsRecordDecl();
+ if (CodeGenOpts.PassByValueIsNoAlias && Decl &&
+ Decl->getArgPassingRestrictions() == RecordDecl::APK_CanPassInRegs)
+ // When calling the function, the pointer passed in will be the only
+ // reference to the underlying object. Mark it accordingly.
+ Attrs.addAttribute(llvm::Attribute::NoAlias);
+
// TODO: We could add the byref attribute if not byval, but it would
// require updating many testcases.
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -4314,6 +4314,9 @@
def fcompatibility_qualified_id_block_param_type_checking : Flag<["-"], "fcompatibility-qualified-id-block-type-checking">,
HelpText<"Allow using blocks with parameters of more specific type than "
"the type system guarantees when a parameter is qualified id">;
+def fpass_by_value_is_noalias: Flag<["-"], "fpass-by-value-is-noalias">,
+ HelpText<"Allows assuming by-value parameters do not alias any other value."
+ "Has no effect on non-trivially-copyable classes in C++.">, Group<f_Group>;
// FIXME: Remove these entirely once functionality/tests have been excised.
def fobjc_gc_only : Flag<["-"], "fobjc-gc-only">, Group<f_Group>,
Index: clang/include/clang/Basic/CodeGenOptions.def
===================================================================
--- clang/include/clang/Basic/CodeGenOptions.def
+++ clang/include/clang/Basic/CodeGenOptions.def
@@ -395,6 +395,10 @@
/// Whether to not follow the AAPCS that enforce at least one read before storing to a volatile bitfield
CODEGENOPT(ForceAAPCSBitfieldLoad, 1, 0)
+/// Assume that by-value parameters do not alias any other values.
+CODEGENOPT(PassByValueIsNoAlias, 1, 0)
+
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
#undef VALUE_CODEGENOPT
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