[ARM] Using cp15 while mtp =auto and arch is arm_arch6k and support thumb2

We follow GCC mtp=auto when arch is arm_arch6k and support thumb2

Reference: https://reviews.llvm.org/D114116

Author: Zhenhang1213

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

@@ -202,13 +202,25 @@ bool arm::useAAPCSForMachO(const llvm::Triple &T) {
          T.getOS() == llvm::Triple::UnknownOS || isARMMProfile(T);
 }
 
-// We follow GCC and support when the backend has support for the MRC/MCR
+// Check whether the architecture backend has support for the MRC/MCR
 // instructions that are used to set the hard thread pointer ("CP15 C13
 // Thread id").
+// This is not identical to ability to use the instruction, as the ARMV6K
+// variants can only use it in Arm mode since they don't support Thumb2
+// encoding.
 bool arm::isHardTPSupported(const llvm::Triple &Triple) {
   int Ver = getARMSubArchVersionNumber(Triple);
   llvm::ARM::ArchKind AK = llvm::ARM::parseArch(Triple.getArchName());
-  return Triple.isARM() || AK == llvm::ARM::ArchKind::ARMV6T2 ||
+  return AK == llvm::ARM::ArchKind::ARMV6K ||
+         AK == llvm::ARM::ArchKind::ARMV6KZ ||
+         (Ver >= 7 && !isARMMProfile(Triple));
+}
+
+// Checks whether the architecture is capable of supporting the Thumb2 encoding
+static bool supportsThumb2Encoding(const llvm::Triple &Triple) {
+  int Ver = arm::getARMSubArchVersionNumber(Triple);
+  llvm::ARM::ArchKind AK = llvm::ARM::parseArch(Triple.getArchName());
+  return AK == llvm::ARM::ArchKind::ARMV6T2 ||
          (Ver >= 7 && AK != llvm::ARM::ArchKind::ARMV8MBaseline);
 }
 
@@ -240,7 +252,13 @@ arm::ReadTPMode arm::getReadTPMode(const Driver &D, const ArgList &Args,
       D.Diag(diag::err_drv_invalid_mtp) << A->getAsString(Args);
     return ReadTPMode::Invalid;
   }
-  return (isHardTPSupported(Triple) ? ReadTPMode::TPIDRURO : ReadTPMode::Soft);
+  // In auto mode we enable HW mode only if both the hardware supports it and
+  // the thumb2 encoding. For example ARMV6T2 supports thumb2, but not hardware.
+  // ARMV6K has HW suport, but not thumb2. Otherwise we could enable it for
+  // ARMV6K in thumb mode.
+  bool autoUseHWTPMode =
+      isHardTPSupported(Triple) && supportsThumb2Encoding(Triple);
+  return autoUseHWTPMode ? ReadTPMode::TPIDRURO : ReadTPMode::Soft;
 }
 
 void arm::setArchNameInTriple(const Driver &D, const ArgList &Args,

clang/test/Driver/arm-thread-pointer.c

@@ -14,25 +14,27 @@
 // RUN: FileCheck -check-prefix=ARMv7_THREAD_POINTER-TPIDRPRW %s
 // ARMv7_THREAD_POINTER-TPIDRPRW: "-target-feature" "+read-tp-tpidrprw"
 
-// RUN: %clang --target=armv6t2-linux -mtp=cp15 -### -S %s 2>&1 | \
-// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER-HARD %s
-// RUN: %clang --target=thumbv6t2-linux -mtp=cp15 -### -S %s 2>&1 | \
-// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER-HARD %s
 // RUN: %clang --target=armv6k-linux -mtp=cp15 -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=ARM_THREAD_POINTER-HARD %s
+// ARM_THREAD_POINTER-HARD: "-target-feature" "+read-tp-tpidruro"
+
+// RUN: %clang --target=thumbv6t2-linux -mtp=cp15 -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER_NO_HARD %s
+// RUN: %clang --target=armv6t2-linux -mtp=cp15 -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER_NO_HARD %s
 // RUN: %clang --target=armv6-linux -mtp=cp15 -### -S %s 2>&1 | \
-// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER-HARD %s
+// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER_NO_HARD %s
 // RUN: %clang --target=armv5t-linux -mtp=cp15 -### -S %s 2>&1 | \
-// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER-HARD %s
-// ARM_THREAD_POINTER-HARD: "-target-feature" "+read-tp-tpidruro"
+// RUN: FileCheck -check-prefix=ARM_THREAD_POINTER_NO_HARD %s
+// ARM_THREAD_POINTER_NO_HARD-NOT: "-target-feature" "+read-tp-tpidruro"
 
 // RUN: %clang --target=armv5t-linux -mtp=cp15 -x assembler -### %s 2>&1 | \
 // RUN: FileCheck -check-prefix=ARMv5_THREAD_POINTER_ASSEMBLER %s
 // ARMv5_THREAD_POINTER_ASSEMBLER-NOT: hardware TLS register is not supported for the armv5 sub-architecture
 
-// RUN: not %clang --target=armv6-linux -mthumb -mtp=cp15 -### -S %s 2>&1 | \
+// not RUN: %clang --target=armv6-linux -mthumb -mtp=cp15 -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=THUMBv6_THREAD_POINTER_UNSUPP %s
-// RUN: not %clang --target=thumbv6-linux -mthumb -mtp=cp15 -### -S %s 2>&1 | \
+// not RUN: %clang --target=thumbv6-linux -mthumb -mtp=cp15 -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=THUMBv6_THREAD_POINTER_UNSUPP %s
 // THUMBv6_THREAD_POINTER_UNSUPP: hardware TLS register is not supported for the thumbv6 sub-architecture
 
@@ -47,3 +49,22 @@
 // RUN: %clang --target=armv7-linux -mtp=auto -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=ARMv7_THREAD_POINTER_Auto %s
 // ARMv7_THREAD_POINTER_Auto: "-target-feature" "+read-tp-tpidruro"
+
+// RUN: %clang --target=armv5t-linux -mtp=auto -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv5t_THREAD_POINTER_Auto %s
+// ARMv5t_THREAD_POINTER_Auto-NOT: "-target-feature" "+read-tp-tpidruro"
+
+// RUN: %clang --target=armv6k-linux -mtp=auto -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv6k_THREAD_POINTER_Auto %s
+// ARMv6k_THREAD_POINTER_Auto: "-target-feature" "+read-tp-tpidruro"
+
+// RUN: %clang --target=armv6-linux -mtp=auto -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv6_THREAD_POINTER_Auto %s
+// ARMv6_THREAD_POINTER_Auto-NOT: "-target-feature" "+read-tp-tpidruro"
+
+// RUN: %clang --target=armv6kz-linux -mtp=auto -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv6kz_THREAD_POINTER_Auto %s
+// ARMv6kz_THREAD_POINTER_Auto: "-target-feature" "+read-tp-tpidruro"
+// RUN: %clang --target=armv6kz-linux -mtp=cp15 -### -S %s 2>&1 | \
+// RUN: FileCheck -check-prefix=ARMv6kz_THREAD_POINTER_Cp15 %s
+// ARMv6kz_THREAD_POINTER_Cp15: "-target-feature" "+read-tp-tpidruro"