[cilksan] Add hook for LLVM intrinsic for x86 pause instruction. Fix …

…issue OpenCilk/infrastructure#21.

cilksan/libhooks.cpp

@@ -330,6 +330,14 @@ CILKSAN_API void __csan_llvm_x86_avx2_gather_d_pd_256(
       call_id, MAAP_count, prop, result, vbase, base, index, mask, scale);
 }
 
+CILKSAN_API void __csan_llvm_x86_sse2_pause(const csi_id_t call_id,
+                                            const csi_id_t func_id,
+                                            unsigned MAAP_count,
+                                            const call_prop_t prop) {
+  // Nothing to do to check a pause instruction.
+  return;
+}
+
 CILKSAN_API void __csan_llvm_stacksave(const csi_id_t call_id,
                                        const csi_id_t func_id,
                                        unsigned MAAP_count,

test/cilksan/TestCases/intrinsics.c

@@ -0,0 +1,32 @@
+// RUN: %clang_cilksan -fopencilk -O0 %s -o %t
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#include <cilk/cilk.h>
+#include <stdio.h>
+
+_Atomic int x = 0;
+
+void foo(void) {
+  while (!x) {
+#ifdef __SSE__
+    __builtin_ia32_pause();
+#endif
+#ifdef __aarch64__
+    __builtin_arm_yield();
+#endif
+  }
+  ++x;
+}
+
+int main(int argc, char *argv[]) {
+  cilk_spawn { ++x; }
+  foo();
+  cilk_sync;
+  printf("x=%d\n", x);
+  return 0;
+}
+
+// CHECK: Running Cilksan race detector
+// CHECK-NEXT: x=2
+// CHECK: Cilksan detected 0 distinct races.
+// CHECK-NEXT: Cilksan suppressed 0 duplicate race reports.