Auto merge of #105446 - erikdesjardins:vt-size, r=nikic

Add 0..=isize::MAX range metadata to size loads from vtables

This is the (much belated) size counterpart to #91569.

Inspired by https://rust-lang.zulipchat.com/#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/Range.20metadata.20for.20.60size_of_val.60.20and.20other.20isize.3A.3AMAX.20limits. This could help optimize layout computations based on the size of a dyn trait. Though, admittedly, adding this to vtables wouldn't be as beneficial as adding it to slice len, which is used much more often.

Miri detects this UB already: https://github.com/rust-lang/rust/blob/b7cc99142ad0cfe47e2fe9f7a82eaf5b672c0573/compiler/rustc_const_eval/src/interpret/traits.rs#L119-L121
(In fact Miri goes further, [assuming a 48-bit address space on 64-bit platforms](https://github.com/rust-lang/rust/blob/9db224fc908059986c179fc6ec433944e9cfce50/compiler/rustc_abi/src/lib.rs#L312-L331), but I don't think we can assume that in an optimization.)

2 files changed, 52 insertions, 1 deletions

diff --git a/src/test/codegen/dst-vtable-align-nonzero.rs b/src/test/codegen/dst-vtable-align-nonzero.rs
index 14c4c3f30f9..54f6e7f992f 100644
--- a/src/test/codegen/dst-vtable-align-nonzero.rs
+++ b/src/test/codegen/dst-vtable-align-nonzero.rs
@@ -1,6 +1,7 @@
-// compile-flags: -O
+// compile-flags: -O -Z merge-functions=disabled
 
 #![crate_type = "lib"]
+#![feature(core_intrinsics)]
 
 // This test checks that we annotate alignment loads from vtables with nonzero range metadata,
 // and that this allows LLVM to eliminate redundant `align >= 1` checks.
@@ -42,4 +43,19 @@ pub fn does_not_eliminate_runtime_check_when_align_2(
     &x.dst
 }
 
+// CHECK-LABEL: @align_load_from_align_of_val
+#[no_mangle]
+pub fn align_load_from_align_of_val(x: &dyn Trait) -> usize {
+    // CHECK: {{%[0-9]+}} = load [[USIZE]], {{.+}} !range [[RANGE_META]]
+    core::mem::align_of_val(x)
+}
+
+// CHECK-LABEL: @align_load_from_vtable_align_intrinsic
+#[no_mangle]
+pub unsafe fn align_load_from_vtable_align_intrinsic(x: &dyn Trait) -> usize {
+    let (data, vtable): (*const (), *const ()) = core::mem::transmute(x);
+    // CHECK: {{%[0-9]+}} = load [[USIZE]], {{.+}} !range [[RANGE_META]]
+    core::intrinsics::vtable_align(vtable)
+}
+
 // CHECK: [[RANGE_META]] = !{[[USIZE]] 1, [[USIZE]] 0}
diff --git a/src/test/codegen/dst-vtable-size-range.rs b/src/test/codegen/dst-vtable-size-range.rs
new file mode 100644
index 00000000000..671c8abdebd
--- /dev/null
+++ b/src/test/codegen/dst-vtable-size-range.rs
@@ -0,0 +1,35 @@
+// compile-flags: -O -Z merge-functions=disabled
+
+#![crate_type = "lib"]
+#![feature(core_intrinsics)]
+
+// Check that we annotate size loads from vtables with 0..(isize::MAX + 1) range metadata.
+
+pub trait Trait {
+    fn f(&self);
+}
+
+// Note that rustc uses inclusive bounds, but LLVM uses exclusive bounds for range metadata.
+// CHECK-LABEL: @generate_exclusive_bound
+#[no_mangle]
+pub fn generate_exclusive_bound() -> usize {
+    // CHECK: ret [[USIZE:i[0-9]+]] [[EXCLUSIVE_BOUND:[-0-9]+]]
+    isize::MAX as usize + 1
+}
+
+// CHECK-LABEL: @size_load_from_size_of_val
+#[no_mangle]
+pub fn size_load_from_size_of_val(x: &dyn Trait) -> usize {
+    // CHECK: {{%[0-9]+}} = load [[USIZE]], {{.+}} !range [[RANGE_META:![0-9]+]]
+    core::mem::size_of_val(x)
+}
+
+// CHECK-LABEL: @size_load_from_vtable_size_intrinsic
+#[no_mangle]
+pub unsafe fn size_load_from_vtable_size_intrinsic(x: &dyn Trait) -> usize {
+    let (data, vtable): (*const (), *const ()) = core::mem::transmute(x);
+    // CHECK: {{%[0-9]+}} = load [[USIZE]], {{.+}} !range [[RANGE_META]]
+    core::intrinsics::vtable_size(vtable)
+}
+
+// CHECK: [[RANGE_META]] = !{[[USIZE]] 0, [[USIZE]] [[EXCLUSIVE_BOUND]]}