i386: Fix PR97715

This change fixes a bug in the i386 backend when adding
-fzero-call-used-regs=all on a target that has no x87
registers.

When there is no x87 registers available, we should not
zero stack registers.

gcc/ChangeLog:

	PR target/97715
	* config/i386/i386.c (zero_all_st_registers): Return
	earlier when the FPU is disabled.

gcc/testsuite/ChangeLog:

	PR target/97715
	* gcc.target/i386/zero-scratch-regs-32.c: New test.

gcc/config/i386/i386.c

@@ -3640,6 +3640,11 @@ zero_all_vector_registers (HARD_REG_SET need_zeroed_hardregs)
 static bool
 zero_all_st_registers (HARD_REG_SET need_zeroed_hardregs)
 {
+
+  /* If the FPU is disabled, no need to zero all st registers.  */
+  if (! (TARGET_80387 || TARGET_FLOAT_RETURNS_IN_80387))
+    return false;
+
   unsigned int num_of_st = 0;
   for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
     if ((STACK_REGNO_P (regno) || MMX_REGNO_P (regno))

gcc/testsuite/gcc.target/i386/zero-scratch-regs-32.c

@@ -0,0 +1,11 @@
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fzero-call-used-regs=all -mno-80387" } */
+
+int
+foo (int x)
+{
+  return (x + 1);
+}
+
+/* { dg-final { scan-assembler-not "fldz" } } */
+