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pc64: assign fpsave/fprestore only once in fpuinit()

--- a/sys/src/9/pc64/fpu.c

+++ b/sys/src/9/pc64/fpu.c

@@ -253,25 +253,26 @@

 	ulong regs[4];

 	cr4 = getcr4() | CR4Osfxsr|CR4Oxmmex;

-	putcr4(cr4);

-	fpsave = fpssesave;

-	fprestore = fpsserestore;

-

 	if((m->cpuidcx & (Xsave|Avx)) == (Xsave|Avx) && getconf("*noavx") == nil){

 		cr4 |= CR4Oxsave;

 		putcr4(cr4);

 		m->xcr0 = 7; /* x87, sse, avx */

 		putxcr0(m->xcr0);

-		fpsave = fpxsave;

-		fprestore = fpxrestore;

-

 		cpuid(0xd, 1, regs);

-		if(regs[0] & Xsaveopt)

-			fpsave = fpxsaveopt;

 		if(regs[0] & Xsaves){

 			fpsave = fpxsaves;

 			fprestore = fpxrestores;

+		} else {

+			if(regs[0] & Xsaveopt)

+				fpsave = fpxsaveopt;

+			else

+				fpsave = fpxsave;

+			fprestore = fpxrestore;

 		}

+	} else {

+		putcr4(cr4);

+		fpsave = fpssesave;

+		fprestore = fpsserestore;

 	}

 }