MDEV-8684: Remove delaying maths in ut_delay

Also introduce compiler barrier properly on all architectures.

storage/innobase/include/ut0ut.h

@@ -89,9 +89,11 @@ struct ut_when_dtor {
    independent way by using YieldProcessor. */
 #  define UT_RELAX_CPU() YieldProcessor()
 # else
-#  define UT_RELAX_CPU() __asm__ __volatile__ ("":::"memory")
+#  define UT_RELAX_CPU() ((void)0) /* avoid warning for an empty statement */
 # endif
 
+#define UT_COMPILER_BARRIER() __asm__ __volatile__ ("":::"memory")
+
 # if defined(HAVE_HMT_PRIORITY_INSTRUCTION)
 #  define UT_LOW_PRIORITY_CPU() __asm__ __volatile__ ("or 1,1,1")
 #  define UT_RESUME_PRIORITY_CPU() __asm__ __volatile__ ("or 2,2,2")
@@ -345,7 +347,7 @@ Runs an idle loop on CPU. The argument gives the desired delay
 in microseconds on 100 MHz Pentium + Visual C++.
 @return	dummy value */
 UNIV_INTERN
-ulint
+void
 ut_delay(
 /*=====*/
 	ulint	delay);	/*!< in: delay in microseconds on 100 MHz Pentium */

storage/innobase/ut/ut0ut.cc

@@ -394,25 +394,21 @@ Runs an idle loop on CPU. The argument gives the desired delay
 in microseconds on 100 MHz Pentium + Visual C++.
 @return	dummy value */
 UNIV_INTERN
-ulint
+void
 ut_delay(
 /*=====*/
 	ulint	delay)	/*!< in: delay in microseconds on 100 MHz Pentium */
 {
-	ulint	i, j;
+	ulint	i;
 
 	UT_LOW_PRIORITY_CPU();
 
-	j = 0;
-
 	for (i = 0; i < delay * 50; i++) {
-		j += i;
 		UT_RELAX_CPU();
+		UT_COMPILER_BARRIER();
 	}
 
 	UT_RESUME_PRIORITY_CPU();
-
-	return(j);
 }
 #endif /* !UNIV_HOTBACKUP */
 

storage/xtradb/include/ut0ut.h

@@ -86,9 +86,11 @@ struct ut_when_dtor {
    independent way by using YieldProcessor. */
 #  define UT_RELAX_CPU() YieldProcessor()
 # else
-#  define UT_RELAX_CPU() __asm__ __volatile__ ("":::"memory")
+#  define UT_RELAX_CPU() ((void)0) /* avoid warning for an empty statement */
 # endif
 
+#define UT_COMPILER_BARRIER() __asm__ __volatile__ ("":::"memory")
+
 # if defined(HAVE_HMT_PRIORITY_INSTRUCTION)
 #  define UT_LOW_PRIORITY_CPU() __asm__ __volatile__ ("or 1,1,1")
 #  define UT_RESUME_PRIORITY_CPU() __asm__ __volatile__ ("or 2,2,2")
@@ -337,7 +339,7 @@ Runs an idle loop on CPU. The argument gives the desired delay
 in microseconds on 100 MHz Pentium + Visual C++.
 @return	dummy value */
 UNIV_INTERN
-ulint
+void
 ut_delay(
 /*=====*/
 	ulint	delay);	/*!< in: delay in microseconds on 100 MHz Pentium */

storage/xtradb/ut/ut0ut.cc

@@ -395,25 +395,21 @@ Runs an idle loop on CPU. The argument gives the desired delay
 in microseconds on 100 MHz Pentium + Visual C++.
 @return	dummy value */
 UNIV_INTERN
-ulint
+void
 ut_delay(
 /*=====*/
 	ulint	delay)	/*!< in: delay in microseconds on 100 MHz Pentium */
 {
-	ulint	i, j;
+	ulint	i;
 
 	UT_LOW_PRIORITY_CPU();
 
-	j = 0;
-
 	for (i = 0; i < delay * 50; i++) {
-		j += i;
 		UT_RELAX_CPU();
+		UT_COMPILER_BARRIER();
 	}
 
 	UT_RESUME_PRIORITY_CPU();
-
-	return(j);
 }
 #endif /* !UNIV_HOTBACKUP */