Merge commit 'fda0bb9588912a3e0606e880ca9f6e913cf8a5a4' into subtree-update_cg_gcc_2025-06-18

1 files changed, 90 insertions, 12 deletions

diff --git a/compiler/rustc_codegen_gcc/src/common.rs b/compiler/rustc_codegen_gcc/src/common.rs
index 918195364ff..58ff2f1f8f0 100644
--- a/compiler/rustc_codegen_gcc/src/common.rs
+++ b/compiler/rustc_codegen_gcc/src/common.rs
@@ -9,7 +9,6 @@ use rustc_middle::mir::Mutability;
 use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc, Scalar};
 use rustc_middle::ty::layout::LayoutOf;
 
-use crate::consts::const_alloc_to_gcc;
 use crate::context::CodegenCx;
 use crate::type_of::LayoutGccExt;
 
@@ -46,12 +45,65 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
 }
 
 pub fn bytes_in_context<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, bytes: &[u8]) -> RValue<'gcc> {
-    let context = &cx.context;
-    let byte_type = context.new_type::<u8>();
-    let typ = context.new_array_type(None, byte_type, bytes.len() as u64);
-    let elements: Vec<_> =
-        bytes.iter().map(|&byte| context.new_rvalue_from_int(byte_type, byte as i32)).collect();
-    context.new_array_constructor(None, typ, &elements)
+    // Instead of always using an array of bytes, use an array of larger integers of target endianness
+    // if possible. This reduces the amount of `rvalues` we use, which reduces memory usage significantly.
+    //
+    // FIXME(FractalFir): Consider using `global_set_initializer` instead. Before this is done, we need to confirm that
+    // `global_set_initializer` is more memory efficient than the current solution.
+    // `global_set_initializer` calls `global_set_initializer_rvalue` under the hood - does it generate an array of rvalues,
+    // or is it using a more efficient representation?
+    match bytes.len() % 8 {
+        0 => {
+            let context = &cx.context;
+            let byte_type = context.new_type::<u64>();
+            let typ = context.new_array_type(None, byte_type, bytes.len() as u64 / 8);
+            let elements: Vec<_> = bytes
+                .chunks_exact(8)
+                .map(|arr| {
+                    let arr: [u8; 8] = arr.try_into().unwrap();
+                    context.new_rvalue_from_long(
+                        byte_type,
+                        // Since we are representing arbitrary byte runs as integers, we need to follow the target
+                        // endianness.
+                        match cx.sess().target.options.endian {
+                            rustc_abi::Endian::Little => u64::from_le_bytes(arr) as i64,
+                            rustc_abi::Endian::Big => u64::from_be_bytes(arr) as i64,
+                        },
+                    )
+                })
+                .collect();
+            context.new_array_constructor(None, typ, &elements)
+        }
+        4 => {
+            let context = &cx.context;
+            let byte_type = context.new_type::<u32>();
+            let typ = context.new_array_type(None, byte_type, bytes.len() as u64 / 4);
+            let elements: Vec<_> = bytes
+                .chunks_exact(4)
+                .map(|arr| {
+                    let arr: [u8; 4] = arr.try_into().unwrap();
+                    context.new_rvalue_from_int(
+                        byte_type,
+                        match cx.sess().target.options.endian {
+                            rustc_abi::Endian::Little => u32::from_le_bytes(arr) as i32,
+                            rustc_abi::Endian::Big => u32::from_be_bytes(arr) as i32,
+                        },
+                    )
+                })
+                .collect();
+            context.new_array_constructor(None, typ, &elements)
+        }
+        _ => {
+            let context = cx.context;
+            let byte_type = context.new_type::<u8>();
+            let typ = context.new_array_type(None, byte_type, bytes.len() as u64);
+            let elements: Vec<_> = bytes
+                .iter()
+                .map(|&byte| context.new_rvalue_from_int(byte_type, byte as i32))
+                .collect();
+            context.new_array_constructor(None, typ, &elements)
+        }
+    }
 }
 
 pub fn type_is_pointer(typ: Type<'_>) -> bool {
@@ -185,14 +237,15 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
 
                 // FIXME(antoyo): there's some issues with using the u128 code that follows, so hard-code
                 // the paths for floating-point values.
-                if ty == self.float_type {
+                // TODO: Remove this code?
+                /*if ty == self.float_type {
                     return self
                         .context
                         .new_rvalue_from_double(ty, f32::from_bits(data as u32) as f64);
                 }
                 if ty == self.double_type {
                     return self.context.new_rvalue_from_double(ty, f64::from_bits(data as u64));
-                }
+                }*/
 
                 let value = self.const_uint_big(self.type_ix(bitsize), data);
                 let bytesize = layout.size(self).bytes();
@@ -212,7 +265,20 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
                 let alloc_id = prov.alloc_id();
                 let base_addr = match self.tcx.global_alloc(alloc_id) {
                     GlobalAlloc::Memory(alloc) => {
-                        let init = const_alloc_to_gcc(self, alloc);
+                        // For ZSTs directly codegen an aligned pointer.
+                        // This avoids generating a zero-sized constant value and actually needing a
+                        // real address at runtime.
+                        if alloc.inner().len() == 0 {
+                            assert_eq!(offset.bytes(), 0);
+                            let val = self.const_usize(alloc.inner().align.bytes());
+                            return if matches!(layout.primitive(), Pointer(_)) {
+                                self.context.new_cast(None, val, ty)
+                            } else {
+                                self.const_bitcast(val, ty)
+                            };
+                        }
+
+                        let init = self.const_data_from_alloc(alloc);
                         let alloc = alloc.inner();
                         let value = match alloc.mutability {
                             Mutability::Mut => self.static_addr_of_mut(init, alloc.align, None),
@@ -234,7 +300,7 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
                                 }),
                             )))
                             .unwrap_memory();
-                        let init = const_alloc_to_gcc(self, alloc);
+                        let init = self.const_data_from_alloc(alloc);
                         self.static_addr_of(init, alloc.inner().align, None)
                     }
                     GlobalAlloc::Static(def_id) => {
@@ -257,7 +323,19 @@ impl<'gcc, 'tcx> ConstCodegenMethods for CodegenCx<'gcc, 'tcx> {
     }
 
     fn const_data_from_alloc(&self, alloc: ConstAllocation<'_>) -> Self::Value {
-        const_alloc_to_gcc(self, alloc)
+        // We ignore the alignment for the purpose of deduping RValues
+        // The alignment is not handled / used in any way by `const_alloc_to_gcc`,
+        // so it is OK to overwrite it here.
+        let mut mock_alloc = alloc.inner().clone();
+        mock_alloc.align = rustc_abi::Align::MAX;
+        // Check if the rvalue is already in the cache - if so, just return it directly.
+        if let Some(res) = self.const_cache.borrow().get(&mock_alloc) {
+            return *res;
+        }
+        // Rvalue not in the cache - convert and add it.
+        let res = crate::consts::const_alloc_to_gcc_uncached(self, alloc);
+        self.const_cache.borrow_mut().insert(mock_alloc, res);
+        res
     }
 
     fn const_ptr_byte_offset(&self, base_addr: Self::Value, offset: abi::Size) -> Self::Value {