[ARM] reject -mtp=cp15 if target subarch does not support it

Currently, we permit -mtp=cp15 even for targets that don't implement the
TLS register. When building for ARMv6 or earlier, this means we emit
instructions that will UNDEF at runtime. For Thumb1, passing -mtp=cp15
will trigger an assert in the backend.

So let's add some diagnostics to ensure that -mtp=cp15 is only accepted
for ARMv6T2 or newer.

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D113026

Author: ardbiesheuvel

clang/lib/Driver/ToolChains/Arch/ARM.cpp

@@ -148,13 +148,21 @@ bool arm::useAAPCSForMachO(const llvm::Triple &T) {
 }
 
 // Select mode for reading thread pointer (-mtp=soft/cp15).
-arm::ReadTPMode arm::getReadTPMode(const Driver &D, const ArgList &Args) {
+arm::ReadTPMode arm::getReadTPMode(const Driver &D, const ArgList &Args,
+                                   const llvm::Triple &Triple) {
   if (Arg *A = Args.getLastArg(options::OPT_mtp_mode_EQ)) {
     arm::ReadTPMode ThreadPointer =
         llvm::StringSwitch<arm::ReadTPMode>(A->getValue())
             .Case("cp15", ReadTPMode::Cp15)
             .Case("soft", ReadTPMode::Soft)
             .Default(ReadTPMode::Invalid);
+    if (ThreadPointer == ReadTPMode::Cp15 &&
+        getARMSubArchVersionNumber(Triple) < 7 &&
+        llvm::ARM::parseArch(Triple.getArchName()) !=
+            llvm::ARM::ArchKind::ARMV6T2) {
+      D.Diag(diag::err_target_unsupported_tp_hard) << Triple.getArchName();
+      return ReadTPMode::Invalid;
+    }
     if (ThreadPointer != ReadTPMode::Invalid)
       return ThreadPointer;
     if (StringRef(A->getValue()).empty())
@@ -422,7 +430,7 @@ void arm::getARMTargetFeatures(const Driver &D, const llvm::Triple &Triple,
   bool KernelOrKext =
       Args.hasArg(options::OPT_mkernel, options::OPT_fapple_kext);
   arm::FloatABI ABI = arm::getARMFloatABI(D, Triple, Args);
-  arm::ReadTPMode ThreadPointer = arm::getReadTPMode(D, Args);
+  arm::ReadTPMode ThreadPointer = arm::getReadTPMode(D, Args, Triple);
   llvm::Optional<std::pair<const Arg *, StringRef>> WaCPU, WaFPU, WaHDiv,
       WaArch;
 

clang/lib/Driver/ToolChains/Arch/ARM.h

@@ -53,7 +53,8 @@ FloatABI getARMFloatABI(const Driver &D, const llvm::Triple &Triple,
                         const llvm::opt::ArgList &Args);
 void setFloatABIInTriple(const Driver &D, const llvm::opt::ArgList &Args,
                          llvm::Triple &triple);
-ReadTPMode getReadTPMode(const Driver &D, const llvm::opt::ArgList &Args);
+ReadTPMode getReadTPMode(const Driver &D, const llvm::opt::ArgList &Args,
+                         const llvm::Triple &Triple);
 void setArchNameInTriple(const Driver &D, const llvm::opt::ArgList &Args,
                          types::ID InputType, llvm::Triple &Triple);
 

clang/test/Driver/clang-translation.c

@@ -110,15 +110,27 @@
 // ARMV5E: "-cc1"
 // ARMV5E: "-target-cpu" "arm1022e"
 
-// RUN: %clang -target arm-linux -mtp=cp15 -### -S %s -arch armv7 2>&1 | \
+// RUN: %clang -target armv7-linux -mtp=cp15 -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=ARMv7_THREAD_POINTER-HARD %s
 // ARMv7_THREAD_POINTER-HARD: "-target-feature" "+read-tp-hard"
 
-// RUN: %clang -target arm-linux -mtp=soft -### -S %s -arch armv7 2>&1 | \
+// RUN: %clang -target armv6t2-linux -mtp=cp15 -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv6T2_THREAD_POINTER-HARD %s
+// ARMv6T2_THREAD_POINTER-HARD: "-target-feature" "+read-tp-hard"
+
+// RUN: %clang -target armv5t-linux -mtp=cp15 -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv5_THREAD_POINTER_UNSUPP %s
+// ARMv5_THREAD_POINTER_UNSUPP: hardware TLS register is not supported for the armv5 sub-architecture
+
+// RUN: %clang -target thumbv6-linux -mtp=cp15 -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv6_THREAD_POINTER_UNSUPP %s
+// ARMv6_THREAD_POINTER_UNSUPP: hardware TLS register is not supported for the armv6 sub-architecture
+
+// RUN: %clang -target armv7-linux -mtp=soft -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=ARMv7_THREAD_POINTER_SOFT %s
 // ARMv7_THREAD_POINTER_SOFT-NOT: "-target-feature" "+read-tp-hard"
 
-// RUN: %clang -target arm-linux -### -S %s -arch armv7 2>&1 | \
+// RUN: %clang -target armv7-linux -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=ARMv7_THREAD_POINTER_NON %s
 // ARMv7_THREAD_POINTER_NON-NOT: "-target-feature" "+read-tp-hard"