always build alloca in the entry block (#46)

Signed-off-by: xermicus <cyrill@parity.io>

crates/common/src/byte_length.rs

@@ -6,15 +6,12 @@ pub const BYTE_LENGTH_BYTE: usize = 1;
 /// The x86 word byte-length.
 pub const BYTE_LENGTH_X32: usize = 4;
 
-/// Native stack alignment size in bytes
-#[cfg(not(feature = "riscv-64"))]
-pub const BYTE_LENGTH_STACK_ALIGN: usize = 4;
-#[cfg(feature = "riscv-64")]
-pub const BYTE_LENGTH_STACK_ALIGN: usize = 8;
-
 /// The x86_64 word byte-length.
 pub const BYTE_LENGTH_X64: usize = 8;
 
+/// EVM native stack alignment size in bytes
+pub const BYTE_LENGTH_STACK_ALIGN: usize = 32;
+
 /// The ETH address byte-length.
 pub const BYTE_LENGTH_ETH_ADDRESS: usize = 20;
 

crates/llvm-context/src/polkavm/context/mod.rs

@@ -441,7 +441,7 @@ where
             0 => FunctionReturn::none(),
             1 => {
                 self.set_basic_block(entry_block);
-                let pointer = self.build_alloca(self.word_type(), "return_pointer");
+                let pointer = self.build_alloca_internal(self.word_type(), "return_pointer");
                 FunctionReturn::primitive(pointer)
             }
             size if name.starts_with(Function::ZKSYNC_NEAR_CALL_ABI_PREFIX) => {
@@ -452,7 +452,7 @@ where
             }
             size => {
                 self.set_basic_block(entry_block);
-                let pointer = self.build_alloca(
+                let pointer = self.build_alloca_internal(
                     self.structure_type(
                         vec![self.word_type().as_basic_type_enum(); size].as_slice(),
                     ),
@@ -595,19 +595,42 @@ where
         self.builder.get_insert_block().expect("Always exists")
     }
 
-    /// Builds a stack allocation instruction.
-    /// Sets the alignment to 128 bits.
+    /// Builds an aligned stack allocation at the function entry.
     pub fn build_alloca<T: BasicType<'ctx> + Clone + Copy>(
         &self,
         r#type: T,
         name: &str,
+    ) -> Pointer<'ctx> {
+        let current_block = self.basic_block();
+        let entry_block = self.current_function().borrow().entry_block();
+
+        match entry_block.get_first_instruction() {
+            Some(instruction) => self.builder().position_before(&instruction),
+            None => self.builder().position_at_end(entry_block),
+        }
+
+        let pointer = self.build_alloca_internal(r#type, name);
+
+        self.set_basic_block(current_block);
+        return pointer;
+    }
+
+    /// Builds a stack allocation and sets the alignment.
+    ///
+    /// Stack allocations should always happen at the function prelude.
+    /// Only use this when the position is guaranteed to be at the entry!
+    fn build_alloca_internal<T: BasicType<'ctx> + Clone + Copy>(
+        &self,
+        r#type: T,
+        name: &str,
     ) -> Pointer<'ctx> {
         let pointer = self.builder.build_alloca(r#type, name).unwrap();
-        self.basic_block()
-            .get_last_instruction()
-            .expect("Always exists")
+        pointer
+            .as_instruction()
+            .unwrap()
             .set_alignment(revive_common::BYTE_LENGTH_STACK_ALIGN as u32)
             .expect("Alignment is valid");
+
         Pointer::new(r#type, AddressSpace::Stack, pointer)
     }