cmd/dist: sse auto-detect

R=golang-dev, dsymonds, minux.ma, iant, alex.brainman
CC=golang-dev
https://golang.org/cl/7035055

src/cmd/dist/a.h

@@ -123,6 +123,7 @@ void	runv(Buf *b, char *dir, int mode, Vec *argv);
 void	bgrunv(char *dir, int mode, Vec *argv);
 void	bgwait(void);
 bool	streq(char*, char*);
+bool	cansse(void);
 void	writefile(Buf*, char*, int);
 void	xatexit(void (*f)(void));
 void	xexit(int);

src/cmd/dist/build.c

@@ -104,8 +104,12 @@ init(void)
 	goarm = btake(&b);
 
 	xgetenv(&b, "GO386");
-	if(b.len == 0)
+	if(b.len == 0) {
-		bwritestr(&b, "387");
+		if(cansse())
+			bwritestr(&b, "sse");
+		else
+			bwritestr(&b, "387");
+	}
 	go386 = btake(&b);
 
 	p = bpathf(&b, "%s/include/u.h", goroot);

src/cmd/dist/plan9.c

@@ -758,4 +758,12 @@ xtryexecfunc(void (*f)(void))
 	return 0; // suffice for now
 }
 
+bool
+cansse(void)
+{
+	// if we had access to cpuid, could answer this question
+	// less conservatively.
+	return 0;
+}
+
 #endif // PLAN9

src/cmd/dist/unix.c

@@ -741,6 +741,7 @@ xsamefile(char *f1, char *f2)
 
 sigjmp_buf sigill_jmpbuf;
 static void sigillhand(int);
+
 // xtryexecfunc tries to execute function f, if any illegal instruction
 // signal received in the course of executing that function, it will
 // return 0, otherwise it will return 1.
@@ -757,6 +758,7 @@ xtryexecfunc(void (*f)(void))
 	signal(SIGILL, SIG_DFL);
 	return r;
 }
+
 // SIGILL handler helper
 static void
 sigillhand(int signum)
@@ -765,5 +767,26 @@ sigillhand(int signum)
 	siglongjmp(sigill_jmpbuf, 1);
 }
 
+static void
+__cpuid(int dst[4], int ax)
+{
+#if defined(__i386__) || defined(__x86_64__)
+	asm volatile("cpuid"
+		: "=a" (dst[0]), "=b" (dst[1]), "=c" (dst[2]), "=d" (dst[3])
+		: "0" (ax));
+#else
+	dst[0] = dst[1] = dst[2] = dst[3] = 0;
+#endif
+}
+
+bool
+cansse(void)
+{
+	int info[4];
+	
+	__cpuid(info, 1);
+	return (info[3] & (1<<26)) != 0;	// SSE2
+}
+
 #endif // PLAN9
 #endif // __WINDOWS__

src/cmd/dist/windows.c

@@ -971,4 +971,29 @@ xtryexecfunc(void (*f)(void))
 	return 0; // suffice for now
 }
 
+static void
+cpuid(int dst[4], int ax)
+{
+	// NOTE: This asm statement is for mingw.
+	// If we ever support MSVC, use __cpuid(dst, ax)
+	// to use the built-in.
+#if defined(__i386__) || defined(__x86_64__)
+	asm volatile("cpuid"
+		: "=a" (dst[0]), "=b" (dst[1]), "=c" (dst[2]), "=d" (dst[3])
+		: "0" (ax));
+#else
+	dst[0] = dst[1] = dst[2] = dst[3] = 0;
+#endif
+}
+
+bool
+cansse(void)
+{
+	int info[4];
+	
+	cpuid(info, 1);
+	return (info[3] & (1<<26)) != 0;	// SSE2
+}
+
+
 #endif // __WINDOWS__