Auto merge of rust-lang#122053 - erikdesjardins:alloca, r=nikic

Stop using LLVM struct types for alloca

The alloca type has no semantic meaning, only the size (and alignment, but we specify it explicitly) matter. Using `[N x i8]` is a more direct way to specify that we want `N` bytes, and avoids relying on LLVM's struct layout. It is likely that a future LLVM version will change to an untyped alloca representation.

Split out from rust-lang#121577.

r? `@ghost`

Author: bors

src/builder.rs

@@ -898,26 +898,20 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         self.gcc_checked_binop(oop, typ, lhs, rhs)
     }
 
-    fn alloca(&mut self, ty: Type<'gcc>, align: Align) -> RValue<'gcc> {
-        // FIXME(antoyo): this check that we don't call get_aligned() a second time on a type.
-        // Ideally, we shouldn't need to do this check.
-        let aligned_type = if ty == self.cx.u128_type || ty == self.cx.i128_type {
-            ty
-        } else {
-            ty.get_aligned(align.bytes())
-        };
+    fn alloca(&mut self, size: Size, align: Align) -> RValue<'gcc> {
+        let ty = self.cx.type_array(self.cx.type_i8(), size.bytes()).get_aligned(align.bytes());
         // TODO(antoyo): It might be better to return a LValue, but fixing the rustc API is non-trivial.
         self.stack_var_count.set(self.stack_var_count.get() + 1);
         self.current_func()
             .new_local(
                 self.location,
-                aligned_type,
+                ty,
                 &format!("stack_var_{}", self.stack_var_count.get()),
             )
             .get_address(self.location)
     }
 
-    fn byte_array_alloca(&mut self, _len: RValue<'gcc>, _align: Align) -> RValue<'gcc> {
+    fn dynamic_alloca(&mut self, _len: RValue<'gcc>, _align: Align) -> RValue<'gcc> {
         unimplemented!();
     }
 

src/intrinsic/mod.rs

@@ -531,7 +531,7 @@ impl<'gcc, 'tcx> ArgAbiExt<'gcc, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
                 // We instead thus allocate some scratch space...
                 let scratch_size = cast.size(bx);
                 let scratch_align = cast.align(bx);
-                let llscratch = bx.alloca(cast.gcc_type(bx), scratch_align);
+                let llscratch = bx.alloca(scratch_size, scratch_align);
                 bx.lifetime_start(llscratch, scratch_size);
 
                 // ... where we first store the value...

src/intrinsic/simd.rs

@@ -18,7 +18,7 @@ use rustc_middle::span_bug;
 use rustc_middle::ty::layout::HasTyCtxt;
 use rustc_middle::ty::{self, Ty};
 use rustc_span::{sym, Span, Symbol};
-use rustc_target::abi::Align;
+use rustc_target::abi::{Align, Size};
 
 use crate::builder::Builder;
 #[cfg(not(feature = "master"))]
@@ -558,7 +558,7 @@ pub fn generic_simd_intrinsic<'a, 'gcc, 'tcx>(
                 let ze = bx.zext(result, bx.type_ix(expected_bytes * 8));
 
                 // Convert the integer to a byte array
-                let ptr = bx.alloca(bx.type_ix(expected_bytes * 8), Align::ONE);
+                let ptr = bx.alloca(Size::from_bytes(expected_bytes), Align::ONE);
                 bx.store(ze, ptr, Align::ONE);
                 let array_ty = bx.type_array(bx.type_i8(), expected_bytes);
                 let ptr = bx.pointercast(ptr, bx.cx.type_ptr_to(array_ty));