Current code to determine availability of atomics seems a bit
incorrect, or at least weird.
I don't quite understand why clang looks at the OS specified in the
triple, as availability of atomic instructions doesn't depend on the
OS; it only depends on the arch version and the execution mode. Atomics
are there in ARM mode on v6 and later, and in Thumb mode on v7 and later
(but no ldrexd/strexd in the M profile).
This patch is an attempt to rectify the situation: check only the arch
version - correctly, as thumbv7em fails the old check - and allow
atomics up to 32 bits on the ARMv7 M profiles.
If the OS check has a reason I missed, I'll add it back - but bare
metal wants atomics too ...
Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp (revision 210990)
+++ lib/Basic/Targets.cpp (working copy)
@@ -3457,27 +3457,14 @@
static const Builtin::Info BuiltinInfo[];
static bool shouldUseInlineAtomic(const llvm::Triple &T) {
- if (T.isOSWindows())
- return true;
-
- // On linux, binaries targeting old cpus call functions in libgcc to
- // perform atomic operations. The implementation in libgcc then calls into
- // the kernel which on armv6 and newer uses ldrex and strex. The net result
- // is that if we assume the kernel is at least as recent as the hardware,
- // it is safe to use atomic instructions on armv6 and newer.
- if (!T.isOSLinux() &&
- T.getOS() != llvm::Triple::FreeBSD &&
- T.getOS() != llvm::Triple::NetBSD &&
- T.getOS() != llvm::Triple::Bitrig)
- return false;
StringRef ArchName = T.getArchName();
if (T.getArch() == llvm::Triple::arm ||
T.getArch() == llvm::Triple::armeb) {
StringRef VersionStr;
if (ArchName.startswith("armv"))
- VersionStr = ArchName.substr(4);
+ VersionStr = ArchName.substr(4, 1);
else if (ArchName.startswith("armebv"))
- VersionStr = ArchName.substr(6);
+ VersionStr = ArchName.substr(6, 1);
else
return false;
unsigned Version;
@@ -3489,9 +3476,9 @@
T.getArch() == llvm::Triple::thumbeb);
StringRef VersionStr;
if (ArchName.startswith("thumbv"))
- VersionStr = ArchName.substr(6);
+ VersionStr = ArchName.substr(6, 1);
else if (ArchName.startswith("thumbebv"))
- VersionStr = ArchName.substr(8);
+ VersionStr = ArchName.substr(8, 1);
else
return false;
unsigned Version;
@@ -3835,6 +3822,13 @@
if (!getCPUDefineSuffix(Name))
return false;
+ // Cortex M does not support 8 byte atomics, while general Thumb2 does.
+ StringRef Profile = getCPUProfile(Name);
+ if (Profile == "M" && MaxAtomicInlineWidth) {
+ MaxAtomicPromoteWidth = 32;
+ MaxAtomicInlineWidth = 32;
+ }
+
CPU = Name;
return true;
}
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