runtime: use a specialized runtime panic function

This specifically fixes unix alloc(): previously when allocation fails
it would (recursively) call alloc() again to create an interface due to
lacking escape analysis.
Also, all other cases shouldn't try to allocate just because something
bad happens at runtime.

TODO: implement escape analysis.

src/runtime/panic.go

@@ -1,5 +1,6 @@
 package runtime
 
+// Builtin function panic(msg), used as a compiler intrinsic.
 func _panic(message interface{}) {
 	printstring("panic: ")
 	printitf(message)
@@ -7,28 +8,30 @@ func _panic(message interface{}) {
 	abort()
 }
 
+// Cause a runtime panic, which is (currently) always a string.
+func runtimePanic(msg string) {
+	printstring("panic: runtime error: ")
+	println(msg)
+	abort()
+}
+
 // Check for bounds in *ssa.Index, *ssa.IndexAddr and *ssa.Lookup.
 func lookupBoundsCheck(length, index int) {
 	if index < 0 || index >= length {
-		// printstring() here is safe as this function is excluded from bounds
-		// checking.
-		printstring("panic: runtime error: index out of range\n")
-		abort()
+		runtimePanic("index out of range")
 	}
 }
 
 // Check for bounds in *ssa.Slice.
 func sliceBoundsCheck(length, low, high uint) {
 	if !(0 <= low && low <= high && high <= length) {
-		printstring("panic: runtime error: slice out of range\n")
-		abort()
+		runtimePanic("slice out of range")
 	}
 }
 
 // Check for bounds in *ssa.MakeSlice.
 func sliceBoundsCheckMake(length, capacity uint) {
 	if !(0 <= length && length <= capacity) {
-		printstring("panic: runtime error: slice size out of range\n")
-		abort()
+		runtimePanic("slice size out of range")
 	}
 }

src/runtime/runtime_unix.go

@@ -48,7 +48,7 @@ func abort() {
 func alloc(size uintptr) unsafe.Pointer {
 	buf := _Cfunc_calloc(1, size)
 	if buf == nil {
-		panic("cannot allocate memory")
+		runtimePanic("cannot allocate memory")
 	}
 	return buf
 }