[ARM] Use hardware TLS register in Thumb2 mode when -mtp=cp15 is passed

In ARM mode, passing -mtp=cp15 forces the use of an inline MRC system register read to move the thread pointer value into a register.

Currently, in Thumb2 mode, -mtp=cp15 is ignored, and a call to the __aeabi_read_tp helper is emitted instead.

This is inconsistent, and breaks the Linux/ARM build for Thumb2 targets, as the Linux kernel does not provide an implementation of __aeabi_read_tp,.

Reviewed By: nickdesaulniers, peter.smith

Differential Revision: https://reviews.llvm.org/D112600

(cherry picked from commit d7e089f)

Author: ardbiesheuvel

llvm/lib/Target/ARM/ARMInstrThumb.td

@@ -1520,6 +1520,7 @@ def tTBH_JT : tPseudoInst<(outs),
 let isCall = 1, Defs = [R0, R12, LR, CPSR], Uses = [SP] in
 def tTPsoft : tPseudoInst<(outs), (ins), 4, IIC_Br,
                           [(set R0, ARMthread_pointer)]>,
+                          Requires<[IsThumb, IsReadTPSoft]>,
                           Sched<[WriteBr]>;
 
 //===----------------------------------------------------------------------===//

llvm/lib/Target/ARM/ARMInstrThumb2.td

@@ -4670,6 +4670,9 @@ def t2CDP2 : T2Cop<0b1111, (outs), (ins p_imm:$cop, imm0_15:$opc1,
 }
 
 
+// Reading thread pointer from coprocessor register
+def : T2Pat<(ARMthread_pointer), (t2MRC 15, 0, 13, 0, 3)>,
+      Requires<[IsThumb2, IsReadTPHard]>;
 
 //===----------------------------------------------------------------------===//
 // ARMv8.1 Privilege Access Never extension

llvm/test/CodeGen/ARM/readtp.ll

@@ -1,5 +1,7 @@
 ; RUN: llc -mtriple=armeb-linux-gnueabihf -O2 -mattr=+read-tp-hard %s -o - | FileCheck %s -check-prefix=CHECK-HARD
 ; RUN: llc -mtriple=armeb-linux-gnueabihf -O2 %s -o - | FileCheck %s -check-prefix=CHECK-SOFT
+; RUN: llc -mtriple=thumbv7-linux-gnueabihf -O2 -mattr=+read-tp-hard %s -o - | FileCheck %s -check-prefix=CHECK-HARD
+; RUN: llc -mtriple=thumbv7-linux-gnueabihf -O2 %s -o - | FileCheck %s -check-prefix=CHECK-SOFT
 
 
 ; __thread int counter;

llvm/test/CodeGen/ARM/thread_pointer.ll

@@ -1,4 +1,7 @@
-; RUN: llc -mtriple arm-linux-gnueabi -filetype asm -o - %s | FileCheck %s
+; RUN: llc -mtriple arm-linux-gnueabi -o - %s | FileCheck %s -check-prefix=CHECK-SOFT
+; RUN: llc -mtriple arm-linux-gnueabi -mattr=+read-tp-hard -o - %s | FileCheck %s -check-prefix=CHECK-HARD
+; RUN: llc -mtriple thumbv7-linux-gnueabi -o - %s | FileCheck %s -check-prefix=CHECK-SOFT
+; RUN: llc -mtriple thumbv7-linux-gnueabi -mattr=+read-tp-hard -o - %s | FileCheck %s -check-prefix=CHECK-HARD
 
 declare i8* @llvm.thread.pointer()
 
@@ -8,5 +11,6 @@ entry:
   ret i8* %tmp1
 }
 
-; CHECK: bl __aeabi_read_tp
+; CHECK-SOFT: bl __aeabi_read_tp
+; CHECK-HARD: mrc p15, #0, {{r[0-9]+}}, c13, c0, #3