[BOLT] Fix instrumentation problem with floating point

[maksfb]

Summary

If BOLT instrumentation runtime uses XMM registers, it can interfere
with the user program causing crashes and unexpected behavior. This
happens as the instrumentation code preserves general purpose registers
only.

Build BOLT instrumentation runtime with "-mno-sse".

[Amir]

LGTM

[maksfb]

This change broke user-func-reorder.c test on some platforms. -mno-sse forced some compilers to emit a call to memset() that was not provided by our runtime. According to documentation, freestanding environment should still provide memcpy, memmove,
memset and memcmp, so in the worst case we can expect the compiler to emit calls to those.

bolt/runtime/CMakeLists.txt

add_library(bolt_rt_hugify STATIC
   hugify.cpp
   ${CMAKE_CURRENT_BINARY_DIR}/config.h
   )
 
 set(BOLT_RT_FLAGS
   -ffreestanding
   -fno-exceptions
   -fno-rtti
-  -fno-stack-protector)
+  -fno-stack-protector
+  -mno-sse)
 
 # Don't let the compiler think it can create calls to standard libs
 target_compile_options(bolt_rt_instr PRIVATE ${BOLT_RT_FLAGS} -fPIE)
 target_include_directories(bolt_rt_instr PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 target_compile_options(bolt_rt_hugify PRIVATE ${BOLT_RT_FLAGS})
 target_include_directories(bolt_rt_hugify PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
 
 install(TARGETS bolt_rt_instr DESTINATION lib)

bolt/test/runtime/X86/instrumentation-xmm.c

+#include <stdio.h>
+
+void foo(float a) {
+  printf("a = %f\n", a);
+}
+
+typedef void (*fptr_t)(float);
+fptr_t func = foo;
+
+int main() {
+  func(42);
+  return 0;
+}
+
+/*
+## Check that BOLT instrumentation runtime preserves xmm registers.
+
+REQUIRES: system-linux,bolt-runtime
+
+RUN: %clang %cflags %s -o %t.exe -fno-inline -Wl,-q
+RUN: llvm-bolt %t.exe --instrument -o %t.instrumented
+RUN: %t.instrumented | FileCheck %s
+
+CHECK: a = 42.000000
+*/