[ARM] Aligned mtp behavior and gcc

Fix #123864, resolved of the different form behavior of mtp

Author: Zhenhang1213

clang/include/clang/Driver/Options.td

@@ -4711,7 +4711,7 @@ def mexecute_only : Flag<["-"], "mexecute-only">, Group<m_arm_Features_Group>,
 def mno_execute_only : Flag<["-"], "mno-execute-only">, Group<m_arm_Features_Group>,
   HelpText<"Allow generation of data access to code sections (ARM only)">;
 let Flags = [TargetSpecific] in {
-def mtp_mode_EQ : Joined<["-"], "mtp=">, Group<m_arm_Features_Group>, Values<"soft,cp15,tpidrurw,tpidruro,tpidrprw,el0,el1,el2,el3,tpidr_el0,tpidr_el1,tpidr_el2,tpidr_el3,tpidrro_el0">,
+def mtp_mode_EQ : Joined<["-"], "mtp=">, Group<m_arm_Features_Group>, Values<"soft,cp15,tpidrurw,tpidruro,tpidrprw,el0,el1,el2,el3,tpidr_el0,tpidr_el1,tpidr_el2,tpidr_el3,tpidrro_el0,auto">,
   HelpText<"Thread pointer access method. "
            "For AArch32: 'soft' uses a function call, or 'tpidrurw', 'tpidruro' or 'tpidrprw' use the three CP15 registers. 'cp15' is an alias for 'tpidruro'. "
            "For AArch64: 'tpidr_el0', 'tpidr_el1', 'tpidr_el2', 'tpidr_el3' or 'tpidrro_el0' use the five system registers. 'elN' is an alias for 'tpidr_elN'.">;

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

@@ -223,6 +223,7 @@ arm::ReadTPMode arm::getReadTPMode(const Driver &D, const ArgList &Args,
             .Case("tpidruro", ReadTPMode::TPIDRURO)
             .Case("tpidrprw", ReadTPMode::TPIDRPRW)
             .Case("soft", ReadTPMode::Soft)
+            .Case("auto", ReadTPMode::Auto)
             .Default(ReadTPMode::Invalid);
     if ((ThreadPointer == ReadTPMode::TPIDRURW ||
          ThreadPointer == ReadTPMode::TPIDRURO ||
@@ -239,7 +240,7 @@ arm::ReadTPMode arm::getReadTPMode(const Driver &D, const ArgList &Args,
       D.Diag(diag::err_drv_invalid_mtp) << A->getAsString(Args);
     return ReadTPMode::Invalid;
   }
-  return ReadTPMode::Soft;
+  return ReadTPMode::Auto;
 }
 
 void arm::setArchNameInTriple(const Driver &D, const ArgList &Args,
@@ -580,6 +581,9 @@ llvm::ARM::FPUKind arm::getARMTargetFeatures(const Driver &D,
     Features.push_back("+read-tp-tpidruro");
   if (getReadTPMode(D, Args, Triple, ForAS) == ReadTPMode::TPIDRPRW)
     Features.push_back("+read-tp-tpidrprw");
+  if (getReadTPMode(D, Args, Triple, ForAS) == ReadTPMode::Auto
+      && isHardTPSupported(Triple) && !ForAS)
+    Features.push_back("+read-tp-tpidrprw");
 
   const Arg *ArchArg = Args.getLastArg(options::OPT_march_EQ);
   const Arg *CPUArg = Args.getLastArg(options::OPT_mcpu_EQ);

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

@@ -41,6 +41,7 @@ enum class ReadTPMode {
   TPIDRURW,
   TPIDRURO,
   TPIDRPRW,
+  Auto,
 };
 
 enum class FloatABI {

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

@@ -42,4 +42,8 @@
 
 // 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-tpidruro"
+// ARMv7_THREAD_POINTER_NON: "-target-feature" "+read-tp-tpidruro"
+
+// 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"