trans: Use an isize to count the number of registers so we don't underflow for fn's with > 7 args in debug builds.

src/librustc_trans/trans/cabi_x86_64.rs

@@ -411,7 +411,7 @@ pub fn compute_abi_info(ccx: &CrateContext,
     }
 
     let mut int_regs = 6; // RDI, RSI, RDX, RCX, R8, R9
-    let mut sse_regs = 8;
+    let mut sse_regs = 8; // XMM0-7
 
     let ret_ty = if ret_def {
         x86_64_ty(ccx, rty, |cls| {
@@ -430,8 +430,8 @@ pub fn compute_abi_info(ccx: &CrateContext,
     let mut arg_tys = Vec::new();
     for t in atys {
         let ty = x86_64_ty(ccx, *t, |cls| {
-            let needed_int = cls.iter().filter(|&&c| c == Int).count();
-            let needed_sse = cls.iter().filter(|c| c.is_sse()).count();
+            let needed_int = cls.iter().filter(|&&c| c == Int).count() as isize;
+            let needed_sse = cls.iter().filter(|c| c.is_sse()).count() as isize;
             let in_mem = cls.is_pass_byval() ||
                          int_regs < needed_int ||
                          sse_regs < needed_sse;

src/test/run-make/extern-fn-struct-passing-abi/test.c

@@ -58,6 +58,28 @@ void byval_rect(int32_t a, int32_t b, int32_t c, int32_t d, int32_t e, struct Re
     assert(s.d == 556);
 }
 
+// System V x86_64 ABI:
+// a, b, c, d, e, f should be in registers
+// s should be byval pointer on the stack
+//
+// Win64 ABI:
+// a, b, c, d should be in registers
+// e, f should be on the stack
+// s should be byval pointer on the stack
+void byval_many_rect(int32_t a, int32_t b, int32_t c, int32_t d, int32_t e,
+                     int32_t f, struct Rect s) {
+    assert(a == 1);
+    assert(b == 2);
+    assert(c == 3);
+    assert(d == 4);
+    assert(e == 5);
+    assert(f == 6);
+    assert(s.a == 553);
+    assert(s.b == 554);
+    assert(s.c == 555);
+    assert(s.d == 556);
+}
+
 // System V x86_64 ABI:
 // a, b, c, d, e, f, g should be in sse registers
 // s should be split across 2 registers

src/test/run-make/extern-fn-struct-passing-abi/test.rs

@@ -50,6 +50,8 @@ struct Huge {
 extern {
     fn byval_rect(a: i32, b: i32, c: i32, d: i32, e: i32, s: Rect);
 
+    fn byval_many_rect(a: i32, b: i32, c: i32, d: i32, e: i32, f: i32, s: Rect);
+
     fn byval_rect_floats(a: f32, b: f32, c: f64, d: f32, e: f32,
                          f: f32, g: f64, s: Rect, t: FloatRect);
 
@@ -80,6 +82,7 @@ fn main() {
 
     unsafe {
         byval_rect(1, 2, 3, 4, 5, s);
+        byval_many_rect(1, 2, 3, 4, 5, 6, s);
         byval_rect_floats(1., 2., 3., 4., 5., 6., 7., s, u);
         byval_rect_with_float(1, 2, 3.0, 4, 5, 6, s);
         split_rect(1, 2, s);