Revert "[compiler-rt] Implement ARM atomic operations for architectur…

…es without SMP support"

This reverts commit 910a642.

There are serious correctness issues with the current approach: __sync_*
routines which are not actually atomic should not be enabled by default.

I'll continue discussion on the review.

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

@@ -110,16 +110,6 @@ function(check_compile_definition def argstring out_var)
   cmake_pop_check_state()
 endfunction()
 
-macro(test_arm_smp_support arch cflags_var)
-  if (${arch} STREQUAL "arm")
-    try_compile(HAS_${arch}_SMP ${CMAKE_BINARY_DIR}
-	    ${ARM_SMP_CHECK_SRC} COMPILE_DEFINITIONS "${CMAKE_C_FLAGS} ${_TARGET_${arch}_CFLAGS}")
-    if (HAS_${arch}_SMP)
-      list(APPEND ${cflags_var} -DCOMPILER_RT_HAS_SMP_SUPPORT)
-    endif()
-  endif()
-endmacro()
-
 # test_target_arch(<arch> <def> <target flags...>)
 # Checks if architecture is supported: runs host compiler with provided
 # flags to verify that:

compiler-rt/cmake/config-ix.cmake

@@ -200,11 +200,6 @@ set(COMPILER_RT_SUPPORTED_ARCH)
 set(SIMPLE_SOURCE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/simple.cc)
 file(WRITE ${SIMPLE_SOURCE} "#include <stdlib.h>\n#include <stdio.h>\nint main() { printf(\"hello, world\"); }\n")
 
-# Check if we have SMP support for particular ARM architecture
-# If not use stubs instead of real atomic operations - see sync-ops.h
-set(ARM_SMP_CHECK_SRC ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/arm-barrier.cc)
-file(WRITE ${ARM_SMP_CHECK_SRC} "int main() { asm(\"dmb\"); return 0; }")
-
 # Detect whether the current target platform is 32-bit or 64-bit, and setup
 # the correct commandline flags needed to attempt to target 32-bit and 64-bit.
 if (NOT CMAKE_SIZEOF_VOID_P EQUAL 4 AND

compiler-rt/lib/builtins/CMakeLists.txt

@@ -740,7 +740,6 @@ else ()
         list(APPEND BUILTIN_CFLAGS_${arch} -fomit-frame-pointer -DCOMPILER_RT_ARMHF_TARGET)
       endif()
 
-      test_arm_smp_support(${arch} BUILTIN_CFLAGS_${arch})
       # For RISCV32, we must force enable int128 for compiling long
       # double routines.
       if("${arch}" STREQUAL "riscv32")

compiler-rt/lib/builtins/arm/sync-ops.h

@@ -14,8 +14,6 @@
 
 #include "../assembly.h"
 
-#ifdef COMPILER_RT_HAS_SMP_SUPPORT
-
 #define SYNC_OP_4(op)                                                          \
   .p2align 2;                                                                  \
   .thumb;                                                                      \
@@ -47,37 +45,6 @@
   dmb;                                                                         \
   pop { r4, r5, r6, pc }
 
-#else
-
-#define SYNC_OP_4(op)                                                          \
-  .p2align 2;                                                                  \
-  DEFINE_COMPILERRT_THUMB_FUNCTION(__sync_fetch_and_##op)                      \
-  LOCAL_LABEL(tryatomic_##op) :                                                \
-  mov r12, r0;                                                                 \
-  op(r2, r0, r1);                                                              \
-  str r2, [r12];                                                               \
-  ldr r12, [r12];                                                              \
-  cmp r12, r2;                                                                 \
-  bne LOCAL_LABEL(tryatomic_##op);                                             \
-  bx lr
-
-#define SYNC_OP_8(op)                                                          \
-  .p2align 2;                                                                  \
-  DEFINE_COMPILERRT_THUMB_FUNCTION(__sync_fetch_and_##op)                      \
-  push {r4, r5, r6, lr};                                                       \
-  LOCAL_LABEL(tryatomic_##op) :                                                \
-  mov r12, r0;                                                                 \
-  op(r4, r5, r0, r1, r2, r3);                                                  \
-  stm r12, {r4, r5};                                                           \
-  ldm r12, {r6, r12};                                                          \
-  cmp r6, r4;                                                                  \
-  bne LOCAL_LABEL(tryatomic_##op);                                             \
-  cmp r12, r5;                                                                 \
-  bne LOCAL_LABEL(tryatomic_##op);                                             \
-  pop { r4, r5, r6, pc }
-
-#endif
-
 #define MINMAX_4(rD, rN, rM, cmp_kind)                                         \
   cmp rN, rM;                                                                  \
   mov rD, rM;                                                                  \