Prepare gep for opaque pointers

Implement gep using LLVMBuildGEP2 which takes an explicit type argument
instead of deriving it from a pointer type.

Author: tmiasko

compiler/rustc_codegen_llvm/src/builder.rs

@@ -640,10 +640,11 @@ impl BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         }
     }
 
-    fn gep(&mut self, ptr: &'ll Value, indices: &[&'ll Value]) -> &'ll Value {
+    fn gep(&mut self, ty: &'ll Type, ptr: &'ll Value, indices: &[&'ll Value]) -> &'ll Value {
         unsafe {
-            llvm::LLVMBuildGEP(
+            llvm::LLVMBuildGEP2(
                 self.llbuilder,
+                ty,
                 ptr,
                 indices.as_ptr(),
                 indices.len() as c_uint,

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1394,8 +1394,9 @@ extern "C" {
 
     pub fn LLVMBuildStore(B: &Builder<'a>, Val: &'a Value, Ptr: &'a Value) -> &'a Value;
 
-    pub fn LLVMBuildGEP(
+    pub fn LLVMBuildGEP2(
         B: &Builder<'a>,
+        Ty: &'a Type,
         Pointer: &'a Value,
         Indices: *const &'a Value,
         NumIndices: c_uint,

compiler/rustc_codegen_llvm/src/va_arg.rs

@@ -146,11 +146,11 @@ fn emit_aapcs_va_arg(
     let top = in_reg.load(top_type, top, bx.tcx().data_layout.pointer_align.abi);
 
     // reg_value = *(@top + reg_off_v);
-    let mut reg_addr = in_reg.gep(top, &[reg_off_v]);
+    let mut reg_addr = in_reg.gep(bx.type_i8(), top, &[reg_off_v]);
     if bx.tcx().sess.target.endian == Endian::Big && layout.size.bytes() != slot_size {
         // On big-endian systems the value is right-aligned in its slot.
         let offset = bx.const_i32((slot_size - layout.size.bytes()) as i32);
-        reg_addr = in_reg.gep(reg_addr, &[offset]);
+        reg_addr = in_reg.gep(bx.type_i8(), reg_addr, &[offset]);
     }
     let reg_type = layout.llvm_type(bx);
     let reg_addr = in_reg.bitcast(reg_addr, bx.cx.type_ptr_to(reg_type));

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -121,9 +121,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 bx.inbounds_gep(ptr, &[offset])
             }
             sym::arith_offset => {
+                let ty = substs.type_at(0);
+                let layout = bx.layout_of(ty);
                 let ptr = args[0].immediate();
                 let offset = args[1].immediate();
-                bx.gep(ptr, &[offset])
+                bx.gep(bx.backend_type(layout), ptr, &[offset])
             }
             sym::copy => {
                 copy_intrinsic(

compiler/rustc_codegen_ssa/src/mir/place.rs

@@ -109,7 +109,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
                 Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } if field.is_zst() => {
                     // ZST fields are not included in Scalar, ScalarPair, and Vector layouts, so manually offset the pointer.
                     let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
-                    bx.gep(byte_ptr, &[bx.const_usize(offset.bytes())])
+                    bx.gep(bx.cx().type_i8(), byte_ptr, &[bx.const_usize(offset.bytes())])
                 }
                 Abi::Scalar(_) | Abi::ScalarPair(..) => {
                     // All fields of Scalar and ScalarPair layouts must have been handled by this point.
@@ -189,7 +189,7 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
 
         // Cast and adjust pointer.
         let byte_ptr = bx.pointercast(self.llval, bx.cx().type_i8p());
-        let byte_ptr = bx.gep(byte_ptr, &[offset]);
+        let byte_ptr = bx.gep(bx.cx().type_i8(), byte_ptr, &[offset]);
 
         // Finally, cast back to the type expected.
         let ll_fty = bx.cx().backend_type(field);

compiler/rustc_codegen_ssa/src/traits/builder.rs

@@ -176,7 +176,7 @@ pub trait BuilderMethods<'a, 'tcx>:
         size: Size,
     );
 
-    fn gep(&mut self, ptr: Self::Value, indices: &[Self::Value]) -> Self::Value;
+    fn gep(&mut self, ty: Self::Type, ptr: Self::Value, indices: &[Self::Value]) -> Self::Value;
     fn inbounds_gep(&mut self, ptr: Self::Value, indices: &[Self::Value]) -> Self::Value;
     fn struct_gep(&mut self, ty: Self::Type, ptr: Self::Value, idx: u64) -> Self::Value;