omit unused args warnings for intrinsics without body

compiler/rustc_passes/src/liveness.rs

@@ -1521,6 +1521,14 @@ impl<'tcx> Liveness<'_, 'tcx> {
     }
 
     fn warn_about_unused_args(&self, body: &hir::Body<'_>, entry_ln: LiveNode) {
+        if let Some(intrinsic) =
+            self.ir.tcx.intrinsic(self.ir.tcx.hir().body_owner_def_id(body.id()))
+        {
+            if intrinsic.must_be_overridden {
+                return;
+            }
+        }
+
         for p in body.params {
             self.check_unused_vars_in_pat(
                 p.pat,

tests/ui/liveness/liveness-unused.rs

@@ -2,6 +2,7 @@
 #![deny(unused_variables)]
 #![deny(unused_assignments)]
 #![allow(dead_code, non_camel_case_types, trivial_numeric_casts, dropping_copy_types)]
+#![feature(intrinsics)]
 
 use std::ops::AddAssign;
 
@@ -137,5 +138,10 @@ fn f7() {
     drop(a);
 }
 
+// unused params warnings are not needed for intrinsic functions without bodies
+#[rustc_intrinsic]
+unsafe fn simd_shuffle<T, I, U>(a: T, b: T, i: I) -> U;
+
+
 fn main() {
 }

tests/ui/liveness/liveness-unused.stderr

@@ -1,5 +1,5 @@
 warning: unreachable statement
-  --> $DIR/liveness-unused.rs:92:9
+  --> $DIR/liveness-unused.rs:93:9
    |
 LL |         continue;
    |         -------- any code following this expression is unreachable
@@ -14,7 +14,7 @@ LL | #![warn(unused)]
    = note: `#[warn(unreachable_code)]` implied by `#[warn(unused)]`
 
 error: unused variable: `x`
-  --> $DIR/liveness-unused.rs:8:7
+  --> $DIR/liveness-unused.rs:9:7
    |
 LL | fn f1(x: isize) {
    |       ^ help: if this is intentional, prefix it with an underscore: `_x`
@@ -26,33 +26,33 @@ LL | #![deny(unused_variables)]
    |         ^^^^^^^^^^^^^^^^
 
 error: unused variable: `x`
-  --> $DIR/liveness-unused.rs:12:8
+  --> $DIR/liveness-unused.rs:13:8
    |
 LL | fn f1b(x: &mut isize) {
    |        ^ help: if this is intentional, prefix it with an underscore: `_x`
 
 error: unused variable: `x`
-  --> $DIR/liveness-unused.rs:20:9
+  --> $DIR/liveness-unused.rs:21:9
    |
 LL |     let x: isize;
    |         ^ help: if this is intentional, prefix it with an underscore: `_x`
 
 error: unused variable: `x`
-  --> $DIR/liveness-unused.rs:25:9
+  --> $DIR/liveness-unused.rs:26:9
    |
 LL |     let x = 3;
    |         ^ help: if this is intentional, prefix it with an underscore: `_x`
 
 error: variable `x` is assigned to, but never used
-  --> $DIR/liveness-unused.rs:30:13
+  --> $DIR/liveness-unused.rs:31:13
    |
 LL |     let mut x = 3;
    |             ^
    |
    = note: consider using `_x` instead
 
 error: value assigned to `x` is never read
-  --> $DIR/liveness-unused.rs:32:5
+  --> $DIR/liveness-unused.rs:33:5
    |
 LL |     x += 4;
    |     ^
@@ -65,47 +65,47 @@ LL | #![deny(unused_assignments)]
    |         ^^^^^^^^^^^^^^^^^^
 
 error: variable `z` is assigned to, but never used
-  --> $DIR/liveness-unused.rs:37:13
+  --> $DIR/liveness-unused.rs:38:13
    |
 LL |     let mut z = 3;
    |             ^
    |
    = note: consider using `_z` instead
 
 error: unused variable: `i`
-  --> $DIR/liveness-unused.rs:59:12
+  --> $DIR/liveness-unused.rs:60:12
    |
 LL |       Some(i) => {
    |            ^ help: if this is intentional, prefix it with an underscore: `_i`
 
 error: unused variable: `x`
-  --> $DIR/liveness-unused.rs:79:9
+  --> $DIR/liveness-unused.rs:80:9
    |
 LL |     for x in 1..10 { }
    |         ^ help: if this is intentional, prefix it with an underscore: `_x`
 
 error: unused variable: `x`
-  --> $DIR/liveness-unused.rs:84:10
+  --> $DIR/liveness-unused.rs:85:10
    |
 LL |     for (x, _) in [1, 2, 3].iter().enumerate() { }
    |          ^ help: if this is intentional, prefix it with an underscore: `_x`
 
 error: unused variable: `x`
-  --> $DIR/liveness-unused.rs:89:13
+  --> $DIR/liveness-unused.rs:90:13
    |
 LL |     for (_, x) in [1, 2, 3].iter().enumerate() {
    |             ^ help: if this is intentional, prefix it with an underscore: `_x`
 
 error: variable `x` is assigned to, but never used
-  --> $DIR/liveness-unused.rs:112:9
+  --> $DIR/liveness-unused.rs:113:9
    |
 LL |     let x;
    |         ^
    |
    = note: consider using `_x` instead
 
 error: value assigned to `x` is never read
-  --> $DIR/liveness-unused.rs:116:9
+  --> $DIR/liveness-unused.rs:117:9
    |
 LL |         x = 0;
    |         ^