Remove incorrect use of nocapture attribute

When using an indirect pass mode, a callee can obtain an address of an
argument and capture it. The nocapture attribute promises this does not
happen and so cannot be used unconditionally.

Author: tmiasko

compiler/rustc_target/src/callconv/mod.rs

@@ -367,13 +367,10 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
         let mut attrs = ArgAttributes::new();
 
         // For non-immediate arguments the callee gets its own copy of
-        // the value on the stack, so there are no aliases. It's also
-        // program-invisible so can't possibly capture
-        attrs
-            .set(ArgAttribute::NoAlias)
-            .set(ArgAttribute::NoCapture)
-            .set(ArgAttribute::NonNull)
-            .set(ArgAttribute::NoUndef);
+        // the value on the stack, so there are no aliases. Note that this
+        // pointer *is* program-visible if the function creates a pointer
+        // to its argument!
+        attrs.set(ArgAttribute::NoAlias).set(ArgAttribute::NonNull).set(ArgAttribute::NoUndef);
         attrs.pointee_size = layout.size;
         attrs.pointee_align = Some(layout.align.abi);
 

tests/ui/abi/c-zst.powerpc-linux.stderr

@@ -28,7 +28,7 @@ error: fn_abi_of(pass_zst) = FnAbi {
                    },
                    mode: Indirect {
                        attrs: ArgAttributes {
-                           regular: NoAlias | NoCapture | NonNull | NoUndef,
+                           regular: NoAlias | NonNull | NoUndef,
                            arg_ext: None,
                            pointee_size: Size(0 bytes),
                            pointee_align: Some(

tests/ui/abi/c-zst.s390x-linux.stderr

@@ -28,7 +28,7 @@ error: fn_abi_of(pass_zst) = FnAbi {
                    },
                    mode: Indirect {
                        attrs: ArgAttributes {
-                           regular: NoAlias | NoCapture | NonNull | NoUndef,
+                           regular: NoAlias | NonNull | NoUndef,
                            arg_ext: None,
                            pointee_size: Size(0 bytes),
                            pointee_align: Some(

tests/ui/abi/c-zst.sparc64-linux.stderr

@@ -28,7 +28,7 @@ error: fn_abi_of(pass_zst) = FnAbi {
                    },
                    mode: Indirect {
                        attrs: ArgAttributes {
-                           regular: NoAlias | NoCapture | NonNull | NoUndef,
+                           regular: NoAlias | NonNull | NoUndef,
                            arg_ext: None,
                            pointee_size: Size(0 bytes),
                            pointee_align: Some(

tests/ui/abi/c-zst.x86_64-pc-windows-gnu.stderr

@@ -28,7 +28,7 @@ error: fn_abi_of(pass_zst) = FnAbi {
                    },
                    mode: Indirect {
                        attrs: ArgAttributes {
-                           regular: NoAlias | NoCapture | NonNull | NoUndef,
+                           regular: NoAlias | NonNull | NoUndef,
                            arg_ext: None,
                            pointee_size: Size(0 bytes),
                            pointee_align: Some(

tests/ui/abi/debug.stderr

@@ -465,7 +465,7 @@ error: ABIs are not compatible
                    },
                    mode: Indirect {
                        attrs: ArgAttributes {
-                           regular: NoAlias | NoCapture | NonNull | NoUndef,
+                           regular: NoAlias | NonNull | NoUndef,
                            arg_ext: None,
                            pointee_size: Size(32 bytes),
                            pointee_align: Some(
@@ -540,7 +540,7 @@ error: ABIs are not compatible
                    },
                    mode: Indirect {
                        attrs: ArgAttributes {
-                           regular: NoAlias | NoCapture | NonNull | NoUndef,
+                           regular: NoAlias | NonNull | NoUndef,
                            arg_ext: None,
                            pointee_size: Size(128 bytes),
                            pointee_align: Some(

tests/ui/codegen/indirect-nocapture.rs

@@ -0,0 +1,15 @@
+// Regression test for issue #137668 where an indirect argument have been marked as nocapture
+// despite the fact that callee did in fact capture the address.
+//
+//@ run-pass
+//@ compile-flags: -Copt-level=2
+
+#[inline(never)]
+pub fn f(a: [u32; 64], b: [u32; 64]) -> bool {
+    &a as *const _ as usize != &b as *const _ as usize
+}
+
+fn main() {
+    static S: [u32; 64] = [0; 64];
+    assert!(f(S, S));
+}