Auto merge of #94159 - erikdesjardins:align-load, r=nikic

Add !align metadata on loads of &/&mut/Box

Note that this refers to the alignment of what the loaded value points
to, _not_ the alignment of the loaded value itself.

r? `@ghost` (blocked on #94158)

Author: bors

compiler/rustc_codegen_llvm/src/builder.rs

@@ -477,6 +477,8 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
             bx: &mut Builder<'a, 'll, 'tcx>,
             load: &'ll Value,
             scalar: abi::Scalar,
+            layout: TyAndLayout<'tcx>,
+            offset: Size,
         ) {
             if !scalar.is_always_valid(bx) {
                 bx.noundef_metadata(load);
@@ -488,10 +490,18 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
                         bx.range_metadata(load, scalar.valid_range);
                     }
                 }
-                abi::Pointer if !scalar.valid_range.contains(0) => {
-                    bx.nonnull_metadata(load);
+                abi::Pointer => {
+                    if !scalar.valid_range.contains(0) {
+                        bx.nonnull_metadata(load);
+                    }
+
+                    if let Some(pointee) = layout.pointee_info_at(bx, offset) {
+                        if let Some(_) = pointee.safe {
+                            bx.align_metadata(load, pointee.align);
+                        }
+                    }
                 }
-                _ => {}
+                abi::F32 | abi::F64 => {}
             }
         }
 
@@ -509,7 +519,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
             let llval = const_llval.unwrap_or_else(|| {
                 let load = self.load(place.layout.llvm_type(self), place.llval, place.align);
                 if let abi::Abi::Scalar(scalar) = place.layout.abi {
-                    scalar_load_metadata(self, load, scalar);
+                    scalar_load_metadata(self, load, scalar, place.layout, Size::ZERO);
                 }
                 load
             });
@@ -518,17 +528,17 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
             let b_offset = a.value.size(self).align_to(b.value.align(self).abi);
             let pair_ty = place.layout.llvm_type(self);
 
-            let mut load = |i, scalar: abi::Scalar, align| {
+            let mut load = |i, scalar: abi::Scalar, layout, align, offset| {
                 let llptr = self.struct_gep(pair_ty, place.llval, i as u64);
                 let llty = place.layout.scalar_pair_element_llvm_type(self, i, false);
                 let load = self.load(llty, llptr, align);
-                scalar_load_metadata(self, load, scalar);
+                scalar_load_metadata(self, load, scalar, layout, offset);
                 self.to_immediate_scalar(load, scalar)
             };
 
             OperandValue::Pair(
-                load(0, a, place.align),
-                load(1, b, place.align.restrict_for_offset(b_offset)),
+                load(0, a, place.layout, place.align, Size::ZERO),
+                load(1, b, place.layout, place.align.restrict_for_offset(b_offset), b_offset),
             )
         } else {
             OperandValue::Ref(place.llval, None, place.align)
@@ -1208,6 +1218,18 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
         }
     }
 
+    fn align_metadata(&mut self, load: &'ll Value, align: Align) {
+        unsafe {
+            let v = [self.cx.const_u64(align.bytes())];
+
+            llvm::LLVMSetMetadata(
+                load,
+                llvm::MD_align as c_uint,
+                llvm::LLVMMDNodeInContext(self.cx.llcx, v.as_ptr(), v.len() as c_uint),
+            );
+        }
+    }
+
     fn noundef_metadata(&mut self, load: &'ll Value) {
         unsafe {
             llvm::LLVMSetMetadata(

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -441,6 +441,7 @@ pub enum MetadataType {
     MD_nontemporal = 9,
     MD_mem_parallel_loop_access = 10,
     MD_nonnull = 11,
+    MD_align = 17,
     MD_type = 19,
     MD_noundef = 29,
 }

src/test/codegen/loads.rs

@@ -18,21 +18,47 @@ pub enum MyBool {
     False,
 }
 
+#[repr(align(16))]
+pub struct Align16(u128);
+
+// CHECK: @ptr_alignment_helper({}** {{.*}}align [[PTR_ALIGNMENT:[0-9]+]]
+#[no_mangle]
+pub fn ptr_alignment_helper(x: &&()) {}
+
 // CHECK-LABEL: @load_ref
 #[no_mangle]
 pub fn load_ref<'a>(x: &&'a i32) -> &'a i32 {
-// Alignment of a reference itself is target dependent, so just match any alignment:
-// the main thing we care about here is !nonnull and !noundef.
-// CHECK: load i32*, i32** %x, align {{[0-9]+}}, !nonnull !{{[0-9]+}}, !noundef !{{[0-9]+}}
+// CHECK: load i32*, i32** %x, align [[PTR_ALIGNMENT]], !nonnull !{{[0-9]+}}, !align ![[ALIGN_4_META:[0-9]+]], !noundef !{{[0-9]+}}
+    *x
+}
+
+// CHECK-LABEL: @load_ref_higher_alignment
+#[no_mangle]
+pub fn load_ref_higher_alignment<'a>(x: &&'a Align16) -> &'a Align16 {
+// CHECK: load {{%Align16|i128}}*, {{%Align16|i128}}** %x, align [[PTR_ALIGNMENT]], !nonnull !{{[0-9]+}}, !align ![[ALIGN_16_META:[0-9]+]], !noundef !{{[0-9]+}}
+    *x
+}
+
+// CHECK-LABEL: @load_scalar_pair
+#[no_mangle]
+pub fn load_scalar_pair<'a>(x: &(&'a i32, &'a Align16)) -> (&'a i32, &'a Align16) {
+// CHECK: load i32*, i32** %{{.+}}, align [[PTR_ALIGNMENT]], !nonnull !{{[0-9]+}}, !align ![[ALIGN_4_META]], !noundef !{{[0-9]+}}
+// CHECK: load i64*, i64** %{{.+}}, align [[PTR_ALIGNMENT]], !nonnull !{{[0-9]+}}, !align ![[ALIGN_16_META]], !noundef !{{[0-9]+}}
+    *x
+}
+
+// CHECK-LABEL: @load_raw_pointer
+#[no_mangle]
+pub fn load_raw_pointer<'a>(x: &*const i32) -> *const i32 {
+// loaded raw pointer should not have !nonnull, !align, or !noundef metadata
+// CHECK: load i32*, i32** %x, align [[PTR_ALIGNMENT]]{{$}}
     *x
 }
 
 // CHECK-LABEL: @load_box
 #[no_mangle]
 pub fn load_box<'a>(x: Box<Box<i32>>) -> Box<i32> {
-// Alignment of a box itself is target dependent, so just match any alignment:
-// the main thing we care about here is !nonnull and !noundef.
-// CHECK: load i32*, i32** %x, align {{[0-9]+}}, !nonnull !{{[0-9]+}}, !noundef !{{[0-9]+}}
+// CHECK: load i32*, i32** %x, align [[PTR_ALIGNMENT]], !nonnull !{{[0-9]+}}, !align ![[ALIGN_4_META]], !noundef !{{[0-9]+}}
     *x
 }
 
@@ -120,5 +146,7 @@ pub fn small_struct_alignment(x: Bytes) -> Bytes {
     x
 }
 
-// CHECK: ![[BOOL_RANGE]] = !{i8 0, i8 2}
-// CHECK: ![[NONZEROU16_RANGE]] = !{i16 1, i16 0}
+// CHECK-DAG: ![[BOOL_RANGE]] = !{i8 0, i8 2}
+// CHECK-DAG: ![[NONZEROU16_RANGE]] = !{i16 1, i16 0}
+// CHECK-DAG: ![[ALIGN_4_META]] = !{i64 4}
+// CHECK-DAG: ![[ALIGN_16_META]] = !{i64 16}