[x86] Tweak testcases for PR82361

[Richard Sandiford <richard.sandiford@arm.com>]

gcc/testsuite/gcc.target/i386/pr82361-[12].c check whether we
can optimise away a 32-to-64-bit zero extension of a 32-bit
division or modulus result.  Currently this fails for the modulus
part of f1 and f2 in pr82361-1.c:

/* FIXME: We are still not able to optimize the modulo in f1/f2, only manage
   one.  */
/* { dg-final { scan-assembler-times "movl\t%edx" 2 } } */

pr82361-2.c instead expects no failures:

/* Ditto %edx to %rdx zero extensions.  */
/* { dg-final { scan-assembler-not "movl\t%edx, %edx" } } */

But we actually get the same zero-extensions for f1 and f2 in pr82361-2.c.
The reason they don't trigger a failure is that the RA allocates the
asm input for "d" to %rdi rather than %rdx, so we have:

	movl	%rdi, %rdx

instead of:

	movl	%rdx, %rdx

For the tests to work as expected, I think they have to force "c" and
"d" to be %rax and %rdx respectively.  We then see the same failure in
pr82361-2.c as for pr82361-1.c (but doubled, due to the 8-bit division
path).

Tested on x86_64-linux-gnu.  OK to install?

Richard


2019-09-17  Richard Sandiford  <richard.sandiford@arm.com>

gcc/testsuite/
	* gcc.target/i386/pr82361-1.c (f1, f2, f3, f4, f5, f6): Force
	"c" to be in %rax and "d" to be in %rdx.
	* gcc.target/i386/pr82361-2.c: Expect 4 instances of "movl\t%edx".

Index: gcc/testsuite/gcc.target/i386/pr82361-1.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr82361-1.c	2019-03-08 18:14:39.040959532 +0000
+++ gcc/testsuite/gcc.target/i386/pr82361-1.c	2019-09-17 17:32:00.930930762 +0100
@@ -11,43 +11,43 @@
 void
 f1 (unsigned int a, unsigned int b)
 {
-  unsigned long long c = a / b;
-  unsigned long long d = a % b;
+  register unsigned long long c asm ("rax") = a / b;
+  register unsigned long long d asm ("rdx") = a % b;
   asm volatile ("" : : "r" (c), "r" (d));
 }
 
 void
 f2 (int a, int b)
 {
-  unsigned long long c = (unsigned int) (a / b);
-  unsigned long long d = (unsigned int) (a % b);
+  register unsigned long long c asm ("rax") = (unsigned int) (a / b);
+  register unsigned long long d asm ("rdx") = (unsigned int) (a % b);
   asm volatile ("" : : "r" (c), "r" (d));
 }
 
 void
 f3 (unsigned int a, unsigned int b)
 {
-  unsigned long long c = a / b;
+  register unsigned long long c asm ("rax") = a / b;
   asm volatile ("" : : "r" (c));
 }
 
 void
 f4 (int a, int b)
 {
-  unsigned long long c = (unsigned int) (a / b);
+  register unsigned long long c asm ("rax") = (unsigned int) (a / b);
   asm volatile ("" : : "r" (c));
 }
 
 void
 f5 (unsigned int a, unsigned int b)
 {
-  unsigned long long d = a % b;
+  register unsigned long long d asm ("rdx") = a % b;
   asm volatile ("" : : "r" (d));
 }
 
 void
 f6 (int a, int b)
 {
-  unsigned long long d = (unsigned int) (a % b);
+  register unsigned long long d asm ("rdx") = (unsigned int) (a % b);
   asm volatile ("" : : "r" (d));
 }
Index: gcc/testsuite/gcc.target/i386/pr82361-2.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr82361-2.c	2019-09-17 16:34:52.280124553 +0100
+++ gcc/testsuite/gcc.target/i386/pr82361-2.c	2019-09-17 17:32:00.930930762 +0100
@@ -4,7 +4,8 @@
 /* We should be able to optimize all %eax to %rax zero extensions, because
    div and idiv instructions with 32-bit operands zero-extend both results.   */
 /* { dg-final { scan-assembler-not "movl\t%eax, %eax" } } */
-/* Ditto %edx to %rdx zero extensions.  */
-/* { dg-final { scan-assembler-not "movl\t%edx, %edx" } } */
+/* FIXME: We are still not able to optimize the modulo in f1/f2, only manage
+   one.  */
+/* { dg-final { scan-assembler-times "movl\t%edx" 4 } } */
 
 #include "pr82361-1.c"