i386: Restore Skylake SImode hard register store cost

On Skylake, we should move integer register to SSE register without
going through memory.  This patch restores Skylake SImode hard register
store cost to 6.

gcc/

	PR target/90878
	* config/i386/x86-tune-costs.h (skylake_cost): Restore SImode
	hard register store cost to 6.

gcc/testsuite/

	PR target/90878
	* gcc.target/i386/pr90878.c: New test.

From-SVN: r275906

gcc/ChangeLog

 2019-09-18  H.J. Lu  <hongjiu.lu@intel.com>
 
+	PR target/90878
+	* config/i386/x86-tune-costs.h (skylake_cost): Restore SImode
+	hard register store cost to 6.
+
+2019-09-18  H.J. Lu  <hongjiu.lu@intel.com>
+
 	PR target/91446
 	* config/i386/x86-tune-costs.h (skylake_cost): Increase SImode
 	pseudo register store cost from 3 to 6 to make it the same as

gcc/config/i386/x86-tune-costs.h

@@ -1594,7 +1594,7 @@ struct processor_costs skylake_cost = {
   {4, 4, 4},				/* cost of loading integer registers
 					   in QImode, HImode and SImode.
 					   Relative to reg-reg move (2).  */
-  {6, 6, 3},				/* cost of storing integer registers */
+  {6, 6, 6},				/* cost of storing integer registers */
   2,					/* cost of reg,reg fld/fst */
   {6, 6, 8},				/* cost of loading fp registers
 					   in SFmode, DFmode and XFmode */

gcc/testsuite/ChangeLog

 2019-09-18  H.J. Lu  <hongjiu.lu@intel.com>
 
+	PR target/90878
+	* gcc.target/i386/pr90878.c: New test.
+
+2019-09-18  H.J. Lu  <hongjiu.lu@intel.com>
+
 	PR target/91446
 	* gcc.target/i386/pr91446.c: New test.
 

gcc/testsuite/gcc.target/i386/pr90878.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -march=skylake" } */
+
+union ieee754_float
+  {
+    float f;
+
+    struct
+      {
+	unsigned int mantissa:23;
+	unsigned int exponent:8;
+	unsigned int negative:1;
+      } ieee;
+};
+
+double
+foo (float f)
+{
+  union ieee754_float u;
+  u.f = f;
+  u.ieee.negative = 0;
+  return u.f;
+}
+
+/* { dg-final { scan-assembler-not "vcvtss2sd\[^\\n\]*\\\(%.sp\\\)" } } */