auto merge of #10966 : michaelwoerister/rust/prelude2, r=cmr

This PR improves the stepping experience in GDB. It contains some fine tuning of line information and makes *rustc* produce nearly the same IR/DWARF as Clang. The focus of the changes is function prologue handling which has caused some problems in the past (https://github.com/mozilla/rust/issues/9641).

It seems that GDB does not properly handle function prologues when the function uses segmented stacks, i.e. it does not recognize that the `__morestack` check is part of the prologue. When setting a breakpoint like `break foo` it will set the break point before the arguments of `foo()` have been loaded and still contain bogus values. For function with the #[no_split_stack] attribute this problem has never occurred for me so I'm pretty sure that segmented stacks are the cause of the problem. @jdm mentioned that segmented stack won't be completely abandoned after all. I'd be grateful if you could tell me about what the future might bring in this regard (@brson, @cmr).

Anyway, this PR should alleviate this problem at least in the case when setting breakpoints using line numbers and also make it less confusing when setting them via function names because then GDB will break *before* the first statement where one could conceivably argue that arguments need not be initialized yet.

Also, a koala: :koala:

Cheers,
Michael

1 files changed, 244 insertions, 0 deletions

diff --git a/src/test/debug-info/function-arg-initialization.rs b/src/test/debug-info/function-arg-initialization.rs
new file mode 100644
index 00000000000..e0a4afd4bdf
--- /dev/null
+++ b/src/test/debug-info/function-arg-initialization.rs
@@ -0,0 +1,244 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// xfail-android: FIXME(#10381)
+
+// This test case checks if function arguments already have the correct value when breaking at the
+// first line of the function, that is if the function prologue has already been executed at the
+// first line. Note that because of the __morestack part of the prologue GDB incorrectly breaks at
+// before the arguments have been properly loaded when setting the breakpoint via the function name.
+// Therefore the setup here sets them using line numbers (so be careful when changing this file).
+
+// compile-flags:-Z extra-debug-info
+// debugger:set print pretty off
+// debugger:break function-arg-initialization.rs:139
+// debugger:break function-arg-initialization.rs:154
+// debugger:break function-arg-initialization.rs:158
+// debugger:break function-arg-initialization.rs:162
+// debugger:break function-arg-initialization.rs:166
+// debugger:break function-arg-initialization.rs:170
+// debugger:break function-arg-initialization.rs:174
+// debugger:break function-arg-initialization.rs:178
+// debugger:break function-arg-initialization.rs:182
+// debugger:break function-arg-initialization.rs:190
+// debugger:break function-arg-initialization.rs:197
+
+
+// debugger:run
+
+// IMMEDIATE ARGS
+// debugger:print a
+// check:$1 = 1
+// debugger:print b
+// check:$2 = true
+// debugger:print c
+// check:$3 = 2.5
+// debugger:continue
+
+// NON IMMEDIATE ARGS
+// debugger:print a
+// check:$4 = {a = 3, b = 4, c = 5, d = 6, e = 7, f = 8, g = 9, h = 10}
+// debugger:print b
+// check:$5 = {a = 11, b = 12, c = 13, d = 14, e = 15, f = 16, g = 17, h = 18}
+// debugger:continue
+
+// BINDING
+// debugger:print a
+// check:$6 = 19
+// debugger:print b
+// check:$7 = 20
+// debugger:print c
+// check:$8 = 21.5
+// debugger:continue
+
+// ASSIGNMENT
+// debugger:print a
+// check:$9 = 22
+// debugger:print b
+// check:$10 = 23
+// debugger:print c
+// check:$11 = 24.5
+// debugger:continue
+
+// FUNCTION CALL
+// debugger:print x
+// check:$12 = 25
+// debugger:print y
+// check:$13 = 26
+// debugger:print z
+// check:$14 = 27.5
+// debugger:continue
+
+// EXPR
+// debugger:print x
+// check:$15 = 28
+// debugger:print y
+// check:$16 = 29
+// debugger:print z
+// check:$17 = 30.5
+// debugger:continue
+
+// RETURN EXPR
+// debugger:print x
+// check:$18 = 31
+// debugger:print y
+// check:$19 = 32
+// debugger:print z
+// check:$20 = 33.5
+// debugger:continue
+
+// ARITHMETIC EXPR
+// debugger:print x
+// check:$21 = 34
+// debugger:print y
+// check:$22 = 35
+// debugger:print z
+// check:$23 = 36.5
+// debugger:continue
+
+// IF EXPR
+// debugger:print x
+// check:$24 = 37
+// debugger:print y
+// check:$25 = 38
+// debugger:print z
+// check:$26 = 39.5
+// debugger:continue
+
+// WHILE EXPR
+// debugger:print x
+// check:$27 = 40
+// debugger:print y
+// check:$28 = 41
+// debugger:print z
+// check:$29 = 42
+// debugger:continue
+
+// LOOP EXPR
+// debugger:print x
+// check:$30 = 43
+// debugger:print y
+// check:$31 = 44
+// debugger:print z
+// check:$32 = 45
+// debugger:continue
+
+#[allow(unused_variable)];
+
+
+
+
+fn immediate_args(a: int, b: bool, c: f64) {
+    ()
+}
+
+struct BigStruct {
+    a: u64,
+    b: u64,
+    c: u64,
+    d: u64,
+    e: u64,
+    f: u64,
+    g: u64,
+    h: u64
+}
+
+fn non_immediate_args(a: BigStruct, b: BigStruct) {
+    ()
+}
+
+fn binding(a: i64, b: u64, c: f64) {
+    let x = 0;
+}
+
+fn assignment(mut a: u64, b: u64, c: f64) {
+    a = b;
+}
+
+fn function_call(x: u64, y: u64, z: f64) {
+    print("Hi!")
+}
+
+fn identifier(x: u64, y: u64, z: f64) -> u64 {
+    x
+}
+
+fn return_expr(x: u64, y: u64, z: f64) -> u64 {
+    return x;
+}
+
+fn arithmetic_expr(x: u64, y: u64, z: f64) -> u64 {
+    x + y
+}
+
+fn if_expr(x: u64, y: u64, z: f64) -> u64 {
+    if x + y < 1000 {
+        x
+    } else {
+        y
+    }
+}
+
+fn while_expr(mut x: u64, y: u64, z: u64) -> u64 {
+    while x + y < 1000 {
+        x += z
+    }
+    return x;
+}
+
+fn loop_expr(mut x: u64, y: u64, z: u64) -> u64 {
+    loop {
+        x += z;
+
+        if x + y > 1000 {
+            return x;
+        }
+    }
+}
+
+fn main() {
+    immediate_args(1, true, 2.5);
+
+    non_immediate_args(
+        BigStruct {
+            a: 3,
+            b: 4,
+            c: 5,
+            d: 6,
+            e: 7,
+            f: 8,
+            g: 9,
+            h: 10
+        },
+        BigStruct {
+            a: 11,
+            b: 12,
+            c: 13,
+            d: 14,
+            e: 15,
+            f: 16,
+            g: 17,
+            h: 18
+        }
+    );
+
+    binding(19, 20, 21.5);
+    assignment(22, 23, 24.5);
+    function_call(25, 26, 27.5);
+    identifier(28, 29, 30.5);
+    return_expr(31, 32, 33.5);
+    arithmetic_expr(34, 35, 36.5);
+    if_expr(37, 38, 39.5);
+    while_expr(40, 41, 42);
+    loop_expr(43, 44, 45);
+}
+
+
+