[PATCH] D90630: [CodeGen] Fix Bug 47499: __unaligned extension inconsistent behaviour with C and C++
Jan Ole Hüser via Phabricator via cfe-commits
cfe-commits at lists.llvm.org
Mon Nov 2 10:20:35 PST 2020
j0le created this revision.
j0le added reviewers: rogfer01, rnk.
j0le added a project: clang.
Herald added a subscriber: cfe-commits.
j0le requested review of this revision.
Hello everyone,
I think, I have found the reason, why there is a difference between C and C++ for the keyword __unaligned:
For C, the Method getAsCXXREcordDecl() returns nullptr. That guarantees that hasUnaligned() is called.
If the language is C++, it is not guaranteed, that hasUnaligend() is called and evaluated.
I have some questions:
- Does this CXXRecordDecl contain information, whether the keyword __unaligned is used?
- Does getClassPointerAlignment() has some side effects, that are needed?
Here are some links:
https://bugs.llvm.org/show_bug.cgi?id=47499
Thread on the cfe-dev mailing list: http://lists.llvm.org/pipermail/cfe-dev/2020-September/066783.html
Diff, that introduced the check hasUnaligned() in getNaturalTypeAlignment(): https://reviews.llvm.org/D30166
Kind Regards
Ole
(Jan Ole Hüser)
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D90630
Files:
clang/lib/CodeGen/CodeGenModule.cpp
clang/test/CodeGen/unaligned-struct-copy.c
Index: clang/test/CodeGen/unaligned-struct-copy.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/unaligned-struct-copy.c
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -xc -O2 -triple thumbv7a-unknown-windows-eabi -fms-extensions -emit-llvm < %s | FileCheck %s
+// RUN: %clang_cc1 -xc++ -O2 -triple thumbv7a-unknown-windows-eabi -fms-extensions -emit-llvm < %s | FileCheck %s
+// RUN: %clang_cc1 -xc -O2 -triple x86_64-unknown-linux-gnu -fms-extensions -emit-llvm < %s | FileCheck %s
+// RUN: %clang_cc1 -xc++ -O2 -triple x86_64-unknown-linux-gnu -fms-extensions -emit-llvm < %s | FileCheck %s
+
+struct S1 {
+ unsigned long x;
+};
+
+// CHECK: define
+// CHECK-SAME: void
+// CHECK-SAME: test1
+
+void test1(__unaligned struct S1 *out) {
+ // CHECK: store
+ // CHECK-SAME: align 1
+ out->x = 5;
+ // CHECK: ret void
+}
+
+// CHECK: define
+// CHECK-SAME: void
+// CHECK-SAME: test2
+
+void test2(__unaligned struct S1 *out, __unaligned struct S1 *in) {
+ // CHECK: load
+ // CHECK-SAME: align 1
+ // CHECK: store
+ // CHECK-SAME: align 1
+ *out = *in;
+ // CHECK: ret void
+}
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -6146,16 +6146,17 @@
*BaseInfo = LValueBaseInfo(AlignmentSource::Type);
CharUnits Alignment;
+ const CXXRecordDecl *RD;
+ if (T.getQualifiers().hasUnaligned()) {
+ Alignment = CharUnits::One();
+ }
// For C++ class pointees, we don't know whether we're pointing at a
// base or a complete object, so we generally need to use the
// non-virtual alignment.
- const CXXRecordDecl *RD;
- if (forPointeeType && !AlignForArray && (RD = T->getAsCXXRecordDecl())) {
+ else if (forPointeeType && !AlignForArray && (RD = T->getAsCXXRecordDecl())) {
Alignment = getClassPointerAlignment(RD);
} else {
Alignment = getContext().getTypeAlignInChars(T);
- if (T.getQualifiers().hasUnaligned())
- Alignment = CharUnits::One();
}
// Cap to the global maximum type alignment unless the alignment
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