[clang] [clang][driver] Allow unaligned access on ARMv7 and higher by default (PR #82400)
Paul Kirth via cfe-commits
cfe-commits at lists.llvm.org
Tue Feb 20 12:06:03 PST 2024
https://github.com/ilovepi updated https://github.com/llvm/llvm-project/pull/82400
>From 20634c2f54ae667ee8374d12e58e582aa6cdd051 Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulkirth at google.com>
Date: Tue, 20 Feb 2024 10:34:57 -0800
Subject: [PATCH 1/3] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20in?=
=?UTF-8?q?itial=20version?=
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Created using spr 1.3.4
---
clang/lib/Driver/ToolChains/Arch/ARM.cpp | 14 ++++++--------
clang/test/Driver/arm-alignment.c | 8 ++++++++
2 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/clang/lib/Driver/ToolChains/Arch/ARM.cpp b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
index e6ee2f88a84edf..3bf6056f0c3ecc 100644
--- a/clang/lib/Driver/ToolChains/Arch/ARM.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
@@ -895,20 +895,18 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
// defaults this bit to 0 and handles it as a system-wide (not
// per-process) setting. It is therefore safe to assume that ARMv7+
// Linux targets support unaligned accesses. The same goes for NaCl
- // and Windows.
- //
- // The above behavior is consistent with GCC.
+ // and Windows. However, ARM's forks of GCC and Clang both allow
+ // unaligned accesses by default for all targets. We follow this
+ // behavior and enable unaligned accesses by default for ARMv7+ targets.
+ // Users can disable behavior via compiler options (-mno-unaliged-access).
+ // See https://github.com/llvm/llvm-project/issues/59560 for more info.
int VersionNum = getARMSubArchVersionNumber(Triple);
if (Triple.isOSDarwin() || Triple.isOSNetBSD()) {
if (VersionNum < 6 ||
Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
Features.push_back("+strict-align");
- } else if (Triple.isOSLinux() || Triple.isOSNaCl() ||
- Triple.isOSWindows()) {
- if (VersionNum < 7)
+ } else if (VersionNum < 7)
Features.push_back("+strict-align");
- } else
- Features.push_back("+strict-align");
}
// llvm does not support reserving registers in general. There is support
diff --git a/clang/test/Driver/arm-alignment.c b/clang/test/Driver/arm-alignment.c
index 9177b625729b85..6d0084451e82c7 100644
--- a/clang/test/Driver/arm-alignment.c
+++ b/clang/test/Driver/arm-alignment.c
@@ -22,6 +22,14 @@
// RUN: %clang -target armv7-windows -### %s 2> %t
// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+/// Ensure that by default before ARMv7 we default to +strict-align
+// RUN: %clang -target armv6 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+
+/// After ARMv7 by default we allow unaligned accesses for all targets
+// RUN: %clang -target armv7 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
+
// RUN: %clang --target=aarch64 -munaligned-access -### %s 2> %t
// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-AARCH64 < %t %s
>From a078e658bdcd851d87331ecf87224dc2ddb13c69 Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulkirth at google.com>
Date: Tue, 20 Feb 2024 10:38:50 -0800
Subject: [PATCH 2/3] git clang-format
Created using spr 1.3.4
---
clang/lib/Driver/ToolChains/Arch/ARM.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/lib/Driver/ToolChains/Arch/ARM.cpp b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
index 3bf6056f0c3ecc..a1aea397925931 100644
--- a/clang/lib/Driver/ToolChains/Arch/ARM.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
@@ -906,7 +906,7 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
Features.push_back("+strict-align");
} else if (VersionNum < 7)
- Features.push_back("+strict-align");
+ Features.push_back("+strict-align");
}
// llvm does not support reserving registers in general. There is support
>From c21f9aa16bb4d081f41a108171e88ecac2bf2884 Mon Sep 17 00:00:00 2001
From: Paul Kirth <paulkirth at google.com>
Date: Tue, 20 Feb 2024 12:05:48 -0800
Subject: [PATCH 3/3] Address comments, and update checking
Created using spr 1.3.4
---
clang/docs/ReleaseNotes.rst | 2 ++
clang/lib/Driver/ToolChains/Arch/ARM.cpp | 26 ++++++++----------------
clang/test/Driver/arm-alignment.c | 12 +++++------
3 files changed, 15 insertions(+), 25 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 762e8133f5d536..6a4182474b3345 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -304,6 +304,8 @@ X86 Support
Arm and AArch64 Support
^^^^^^^^^^^^^^^^^^^^^^^
+- ARMv6+ targets now default to allowing unaligned access, except Armv6-M, and
+ Armv8-M without the Main Extension.
Android Support
^^^^^^^^^^^^^^^
diff --git a/clang/lib/Driver/ToolChains/Arch/ARM.cpp b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
index a1aea397925931..8f37895eaee242 100644
--- a/clang/lib/Driver/ToolChains/Arch/ARM.cpp
+++ b/clang/lib/Driver/ToolChains/Arch/ARM.cpp
@@ -886,26 +886,16 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
} else {
// Assume pre-ARMv6 doesn't support unaligned accesses.
//
- // ARMv6 may or may not support unaligned accesses depending on the
- // SCTLR.U bit, which is architecture-specific. We assume ARMv6
- // Darwin and NetBSD targets support unaligned accesses, and others don't.
+ // Assume ARMv6+ supports unaligned accesses, except Armv6-M, and Armv8-M
+ // without the Main Extension. This aligns with the default behavior of
+ // ARM's downstream versions of GCC and Clang
//
- // ARMv7 always has SCTLR.U set to 1, but it has a new SCTLR.A bit
- // which raises an alignment fault on unaligned accesses. Linux
- // defaults this bit to 0 and handles it as a system-wide (not
- // per-process) setting. It is therefore safe to assume that ARMv7+
- // Linux targets support unaligned accesses. The same goes for NaCl
- // and Windows. However, ARM's forks of GCC and Clang both allow
- // unaligned accesses by default for all targets. We follow this
- // behavior and enable unaligned accesses by default for ARMv7+ targets.
- // Users can disable behavior via compiler options (-mno-unaliged-access).
- // See https://github.com/llvm/llvm-project/issues/59560 for more info.
+ // Users can disable behavior via -mno-unaliged-access.
int VersionNum = getARMSubArchVersionNumber(Triple);
- if (Triple.isOSDarwin() || Triple.isOSNetBSD()) {
- if (VersionNum < 6 ||
- Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
- Features.push_back("+strict-align");
- } else if (VersionNum < 7)
+ if (VersionNum < 6 ||
+ Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m ||
+ Triple.getSubArch() ==
+ llvm::Triple::SubArchType::ARMSubArch_v8m_baseline)
Features.push_back("+strict-align");
}
diff --git a/clang/test/Driver/arm-alignment.c b/clang/test/Driver/arm-alignment.c
index 6d0084451e82c7..b2b0da4acb98f0 100644
--- a/clang/test/Driver/arm-alignment.c
+++ b/clang/test/Driver/arm-alignment.c
@@ -22,12 +22,10 @@
// RUN: %clang -target armv7-windows -### %s 2> %t
// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
-/// Ensure that by default before ARMv7 we default to +strict-align
-// RUN: %clang -target armv6 -### %s 2> %t
-// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+// RUN: %clang --target=armv6 -### %s 2> %t
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
-/// After ARMv7 by default we allow unaligned accesses for all targets
-// RUN: %clang -target armv7 -### %s 2> %t
+// RUN: %clang --target=armv7 -### %s 2> %t
// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
// RUN: %clang --target=aarch64 -munaligned-access -### %s 2> %t
@@ -65,10 +63,10 @@
// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
// RUN: %clang -target armv6-unknown-linux -### %s 2> %t
-// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
// RUN: %clang -target armv6-unknown-nacl-gnueabihf -### %s 2> %t
-// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
+// RUN: FileCheck --check-prefix=CHECK-UNALIGNED-ARM < %t %s
// RUN: %clang -target armv6m-apple-darwin -### %s 2> %t
// RUN: FileCheck --check-prefix=CHECK-ALIGNED-ARM < %t %s
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