Auto merge of #94123 - bjorn3:cg_ssa_singleton_builder, r=tmiasko

Partially move cg_ssa towards using a single builder

Not all codegen backends can handle hopping between blocks well. For example Cranelift requires blocks to be terminated before switching to building a new block. Rust-gpu requires a `RefCell` to allow hopping between blocks and cg_gcc currently has a buggy implementation of hopping between blocks. This PR reduces the amount of cases where cg_ssa switches between blocks before they are finished and mostly fixes the block hopping in cg_gcc. (~~only `scalar_to_backend` doesn't handle it correctly yet in cg_gcc~~ fixed that one.)

`@antoyo` please review the cg_gcc changes.

6 files changed, 158 insertions, 150 deletions

diff --git a/compiler/rustc_codegen_gcc/src/builder.rs b/compiler/rustc_codegen_gcc/src/builder.rs
index ffb77e16a14..b430dc329cb 100644
--- a/compiler/rustc_codegen_gcc/src/builder.rs
+++ b/compiler/rustc_codegen_gcc/src/builder.rs
@@ -390,11 +390,6 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         bx
     }
 
-    fn build_sibling_block(&mut self, name: &str) -> Self {
-        let block = self.append_sibling_block(name);
-        Self::build(self.cx, block)
-    }
-
     fn llbb(&self) -> Block<'gcc> {
         self.block.expect("block")
     }
@@ -409,6 +404,11 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         func.new_block(name)
     }
 
+    fn switch_to_block(&mut self, block: Self::BasicBlock) {
+        *self.cx.current_block.borrow_mut() = Some(block);
+        self.block = Some(block);
+    }
+
     fn ret_void(&mut self) {
         self.llbb().end_with_void_return(None)
     }
@@ -880,28 +880,31 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
         let start = dest.project_index(&mut self, zero).llval;
         let end = dest.project_index(&mut self, count).llval;
 
-        let mut header_bx = self.build_sibling_block("repeat_loop_header");
-        let mut body_bx = self.build_sibling_block("repeat_loop_body");
-        let next_bx = self.build_sibling_block("repeat_loop_next");
+        let header_bb = self.append_sibling_block("repeat_loop_header");
+        let body_bb = self.append_sibling_block("repeat_loop_body");
+        let next_bb = self.append_sibling_block("repeat_loop_next");
 
         let ptr_type = start.get_type();
         let current = self.llbb().get_function().new_local(None, ptr_type, "loop_var");
         let current_val = current.to_rvalue();
         self.assign(current, start);
 
-        self.br(header_bx.llbb());
+        self.br(header_bb);
 
-        let keep_going = header_bx.icmp(IntPredicate::IntNE, current_val, end);
-        header_bx.cond_br(keep_going, body_bx.llbb(), next_bx.llbb());
+        self.switch_to_block(header_bb);
+        let keep_going = self.icmp(IntPredicate::IntNE, current_val, end);
+        self.cond_br(keep_going, body_bb, next_bb);
 
+        self.switch_to_block(body_bb);
         let align = dest.align.restrict_for_offset(dest.layout.field(self.cx(), 0).size);
-        cg_elem.val.store(&mut body_bx, PlaceRef::new_sized_aligned(current_val, cg_elem.layout, align));
+        cg_elem.val.store(&mut self, PlaceRef::new_sized_aligned(current_val, cg_elem.layout, align));
 
-        let next = body_bx.inbounds_gep(self.backend_type(cg_elem.layout), current.to_rvalue(), &[self.const_usize(1)]);
-        body_bx.llbb().add_assignment(None, current, next);
-        body_bx.br(header_bx.llbb());
+        let next = self.inbounds_gep(self.backend_type(cg_elem.layout), current.to_rvalue(), &[self.const_usize(1)]);
+        self.llbb().add_assignment(None, current, next);
+        self.br(header_bb);
 
-        next_bx
+        self.switch_to_block(next_bb);
+        self
     }
 
     fn range_metadata(&mut self, _load: RValue<'gcc>, _range: WrappingRange) {
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index c9a04e6280f..780af5bc2af 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -166,9 +166,8 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         Self::append_block(self.cx, self.llfn(), name)
     }
 
-    fn build_sibling_block(&mut self, name: &str) -> Self {
-        let llbb = self.append_sibling_block(name);
-        Self::build(self.cx, llbb)
+    fn switch_to_block(&mut self, llbb: Self::BasicBlock) {
+        *self = Self::build(self.cx, llbb)
     }
 
     fn ret_void(&mut self) {
@@ -544,16 +543,19 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         let start = dest.project_index(&mut self, zero).llval;
         let end = dest.project_index(&mut self, count).llval;
 
-        let mut header_bx = self.build_sibling_block("repeat_loop_header");
-        let mut body_bx = self.build_sibling_block("repeat_loop_body");
-        let next_bx = self.build_sibling_block("repeat_loop_next");
+        let header_bb = self.append_sibling_block("repeat_loop_header");
+        let body_bb = self.append_sibling_block("repeat_loop_body");
+        let next_bb = self.append_sibling_block("repeat_loop_next");
 
-        self.br(header_bx.llbb());
+        self.br(header_bb);
+
+        let mut header_bx = Self::build(self.cx, header_bb);
         let current = header_bx.phi(self.val_ty(start), &[start], &[self.llbb()]);
 
         let keep_going = header_bx.icmp(IntPredicate::IntNE, current, end);
-        header_bx.cond_br(keep_going, body_bx.llbb(), next_bx.llbb());
+        header_bx.cond_br(keep_going, body_bb, next_bb);
 
+        let mut body_bx = Self::build(self.cx, body_bb);
         let align = dest.align.restrict_for_offset(dest.layout.field(self.cx(), 0).size);
         cg_elem
             .val
@@ -564,10 +566,10 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
             current,
             &[self.const_usize(1)],
         );
-        body_bx.br(header_bx.llbb());
-        header_bx.add_incoming_to_phi(current, next, body_bx.llbb());
+        body_bx.br(header_bb);
+        header_bx.add_incoming_to_phi(current, next, body_bb);
 
-        next_bx
+        Self::build(self.cx, next_bb)
     }
 
     fn range_metadata(&mut self, load: &'ll Value, range: WrappingRange) {
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index f471f461e86..e7c13e793d9 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -452,11 +452,11 @@ fn codegen_msvc_try<'ll>(
     let (llty, llfn) = get_rust_try_fn(bx, &mut |mut bx| {
         bx.set_personality_fn(bx.eh_personality());
 
-        let mut normal = bx.build_sibling_block("normal");
-        let mut catchswitch = bx.build_sibling_block("catchswitch");
-        let mut catchpad_rust = bx.build_sibling_block("catchpad_rust");
-        let mut catchpad_foreign = bx.build_sibling_block("catchpad_foreign");
-        let mut caught = bx.build_sibling_block("caught");
+        let normal = bx.append_sibling_block("normal");
+        let catchswitch = bx.append_sibling_block("catchswitch");
+        let catchpad_rust = bx.append_sibling_block("catchpad_rust");
+        let catchpad_foreign = bx.append_sibling_block("catchpad_foreign");
+        let caught = bx.append_sibling_block("caught");
 
         let try_func = llvm::get_param(bx.llfn(), 0);
         let data = llvm::get_param(bx.llfn(), 1);
@@ -520,12 +520,13 @@ fn codegen_msvc_try<'ll>(
         let ptr_align = bx.tcx().data_layout.pointer_align.abi;
         let slot = bx.alloca(bx.type_i8p(), ptr_align);
         let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
-        bx.invoke(try_func_ty, try_func, &[data], normal.llbb(), catchswitch.llbb(), None);
+        bx.invoke(try_func_ty, try_func, &[data], normal, catchswitch, None);
 
-        normal.ret(bx.const_i32(0));
+        bx.switch_to_block(normal);
+        bx.ret(bx.const_i32(0));
 
-        let cs =
-            catchswitch.catch_switch(None, None, &[catchpad_rust.llbb(), catchpad_foreign.llbb()]);
+        bx.switch_to_block(catchswitch);
+        let cs = bx.catch_switch(None, None, &[catchpad_rust, catchpad_foreign]);
 
         // We can't use the TypeDescriptor defined in libpanic_unwind because it
         // might be in another DLL and the SEH encoding only supports specifying
@@ -558,21 +559,24 @@ fn codegen_msvc_try<'ll>(
         // since our exception object effectively contains a Box.
         //
         // Source: MicrosoftCXXABI::getAddrOfCXXCatchHandlerType in clang
+        bx.switch_to_block(catchpad_rust);
         let flags = bx.const_i32(8);
-        let funclet = catchpad_rust.catch_pad(cs, &[tydesc, flags, slot]);
-        let ptr = catchpad_rust.load(bx.type_i8p(), slot, ptr_align);
+        let funclet = bx.catch_pad(cs, &[tydesc, flags, slot]);
+        let ptr = bx.load(bx.type_i8p(), slot, ptr_align);
         let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
-        catchpad_rust.call(catch_ty, catch_func, &[data, ptr], Some(&funclet));
-        catchpad_rust.catch_ret(&funclet, caught.llbb());
+        bx.call(catch_ty, catch_func, &[data, ptr], Some(&funclet));
+        bx.catch_ret(&funclet, caught);
 
         // The flag value of 64 indicates a "catch-all".
+        bx.switch_to_block(catchpad_foreign);
         let flags = bx.const_i32(64);
         let null = bx.const_null(bx.type_i8p());
-        let funclet = catchpad_foreign.catch_pad(cs, &[null, flags, null]);
-        catchpad_foreign.call(catch_ty, catch_func, &[data, null], Some(&funclet));
-        catchpad_foreign.catch_ret(&funclet, caught.llbb());
+        let funclet = bx.catch_pad(cs, &[null, flags, null]);
+        bx.call(catch_ty, catch_func, &[data, null], Some(&funclet));
+        bx.catch_ret(&funclet, caught);
 
-        caught.ret(bx.const_i32(1));
+        bx.switch_to_block(caught);
+        bx.ret(bx.const_i32(1));
     });
 
     // Note that no invoke is used here because by definition this function
@@ -613,15 +617,17 @@ fn codegen_gnu_try<'ll>(
         //      (%ptr, _) = landingpad
         //      call %catch_func(%data, %ptr)
         //      ret 1
-        let mut then = bx.build_sibling_block("then");
-        let mut catch = bx.build_sibling_block("catch");
+        let then = bx.append_sibling_block("then");
+        let catch = bx.append_sibling_block("catch");
 
         let try_func = llvm::get_param(bx.llfn(), 0);
         let data = llvm::get_param(bx.llfn(), 1);
         let catch_func = llvm::get_param(bx.llfn(), 2);
         let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
-        bx.invoke(try_func_ty, try_func, &[data], then.llbb(), catch.llbb(), None);
-        then.ret(bx.const_i32(0));
+        bx.invoke(try_func_ty, try_func, &[data], then, catch, None);
+
+        bx.switch_to_block(then);
+        bx.ret(bx.const_i32(0));
 
         // Type indicator for the exception being thrown.
         //
@@ -629,14 +635,15 @@ fn codegen_gnu_try<'ll>(
         // being thrown.  The second value is a "selector" indicating which of
         // the landing pad clauses the exception's type had been matched to.
         // rust_try ignores the selector.
+        bx.switch_to_block(catch);
         let lpad_ty = bx.type_struct(&[bx.type_i8p(), bx.type_i32()], false);
-        let vals = catch.landing_pad(lpad_ty, bx.eh_personality(), 1);
+        let vals = bx.landing_pad(lpad_ty, bx.eh_personality(), 1);
         let tydesc = bx.const_null(bx.type_i8p());
-        catch.add_clause(vals, tydesc);
-        let ptr = catch.extract_value(vals, 0);
+        bx.add_clause(vals, tydesc);
+        let ptr = bx.extract_value(vals, 0);
         let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
-        catch.call(catch_ty, catch_func, &[data, ptr], None);
-        catch.ret(bx.const_i32(1));
+        bx.call(catch_ty, catch_func, &[data, ptr], None);
+        bx.ret(bx.const_i32(1));
     });
 
     // Note that no invoke is used here because by definition this function
@@ -674,57 +681,54 @@ fn codegen_emcc_try<'ll>(
         //      %catch_data[1] = %is_rust_panic
         //      call %catch_func(%data, %catch_data)
         //      ret 1
-        let mut then = bx.build_sibling_block("then");
-        let mut catch = bx.build_sibling_block("catch");
+        let then = bx.append_sibling_block("then");
+        let catch = bx.append_sibling_block("catch");
 
         let try_func = llvm::get_param(bx.llfn(), 0);
         let data = llvm::get_param(bx.llfn(), 1);
         let catch_func = llvm::get_param(bx.llfn(), 2);
         let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
-        bx.invoke(try_func_ty, try_func, &[data], then.llbb(), catch.llbb(), None);
-        then.ret(bx.const_i32(0));
+        bx.invoke(try_func_ty, try_func, &[data], then, catch, None);
+
+        bx.switch_to_block(then);
+        bx.ret(bx.const_i32(0));
 
         // Type indicator for the exception being thrown.
         //
         // The first value in this tuple is a pointer to the exception object
         // being thrown.  The second value is a "selector" indicating which of
         // the landing pad clauses the exception's type had been matched to.
+        bx.switch_to_block(catch);
         let tydesc = bx.eh_catch_typeinfo();
         let lpad_ty = bx.type_struct(&[bx.type_i8p(), bx.type_i32()], false);
-        let vals = catch.landing_pad(lpad_ty, bx.eh_personality(), 2);
-        catch.add_clause(vals, tydesc);
-        catch.add_clause(vals, bx.const_null(bx.type_i8p()));
-        let ptr = catch.extract_value(vals, 0);
-        let selector = catch.extract_value(vals, 1);
+        let vals = bx.landing_pad(lpad_ty, bx.eh_personality(), 2);
+        bx.add_clause(vals, tydesc);
+        bx.add_clause(vals, bx.const_null(bx.type_i8p()));
+        let ptr = bx.extract_value(vals, 0);
+        let selector = bx.extract_value(vals, 1);
 
         // Check if the typeid we got is the one for a Rust panic.
-        let rust_typeid = catch.call_intrinsic("llvm.eh.typeid.for", &[tydesc]);
-        let is_rust_panic = catch.icmp(IntPredicate::IntEQ, selector, rust_typeid);
-        let is_rust_panic = catch.zext(is_rust_panic, bx.type_bool());
+        let rust_typeid = bx.call_intrinsic("llvm.eh.typeid.for", &[tydesc]);
+        let is_rust_panic = bx.icmp(IntPredicate::IntEQ, selector, rust_typeid);
+        let is_rust_panic = bx.zext(is_rust_panic, bx.type_bool());
 
         // We need to pass two values to catch_func (ptr and is_rust_panic), so
         // create an alloca and pass a pointer to that.
         let ptr_align = bx.tcx().data_layout.pointer_align.abi;
         let i8_align = bx.tcx().data_layout.i8_align.abi;
         let catch_data_type = bx.type_struct(&[bx.type_i8p(), bx.type_bool()], false);
-        let catch_data = catch.alloca(catch_data_type, ptr_align);
-        let catch_data_0 = catch.inbounds_gep(
-            catch_data_type,
-            catch_data,
-            &[bx.const_usize(0), bx.const_usize(0)],
-        );
-        catch.store(ptr, catch_data_0, ptr_align);
-        let catch_data_1 = catch.inbounds_gep(
-            catch_data_type,
-            catch_data,
-            &[bx.const_usize(0), bx.const_usize(1)],
-        );
-        catch.store(is_rust_panic, catch_data_1, i8_align);
-        let catch_data = catch.bitcast(catch_data, bx.type_i8p());
+        let catch_data = bx.alloca(catch_data_type, ptr_align);
+        let catch_data_0 =
+            bx.inbounds_gep(catch_data_type, catch_data, &[bx.const_usize(0), bx.const_usize(0)]);
+        bx.store(ptr, catch_data_0, ptr_align);
+        let catch_data_1 =
+            bx.inbounds_gep(catch_data_type, catch_data, &[bx.const_usize(0), bx.const_usize(1)]);
+        bx.store(is_rust_panic, catch_data_1, i8_align);
+        let catch_data = bx.bitcast(catch_data, bx.type_i8p());
 
         let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
-        catch.call(catch_ty, catch_func, &[data, catch_data], None);
-        catch.ret(bx.const_i32(1));
+        bx.call(catch_ty, catch_func, &[data, catch_data], None);
+        bx.ret(bx.const_i32(1));
     });
 
     // Note that no invoke is used here because by definition this function
diff --git a/compiler/rustc_codegen_llvm/src/va_arg.rs b/compiler/rustc_codegen_llvm/src/va_arg.rs
index f090ae6ecb4..ceb3d5a84ab 100644
--- a/compiler/rustc_codegen_llvm/src/va_arg.rs
+++ b/compiler/rustc_codegen_llvm/src/va_arg.rs
@@ -102,10 +102,10 @@ fn emit_aapcs_va_arg<'ll, 'tcx>(
     let va_list_ty = va_list_layout.llvm_type(bx);
     let layout = bx.cx.layout_of(target_ty);
 
-    let mut maybe_reg = bx.build_sibling_block("va_arg.maybe_reg");
-    let mut in_reg = bx.build_sibling_block("va_arg.in_reg");
-    let mut on_stack = bx.build_sibling_block("va_arg.on_stack");
-    let mut end = bx.build_sibling_block("va_arg.end");
+    let maybe_reg = bx.append_sibling_block("va_arg.maybe_reg");
+    let in_reg = bx.append_sibling_block("va_arg.in_reg");
+    let on_stack = bx.append_sibling_block("va_arg.on_stack");
+    let end = bx.append_sibling_block("va_arg.end");
     let zero = bx.const_i32(0);
     let offset_align = Align::from_bytes(4).unwrap();
 
@@ -125,53 +125,53 @@ fn emit_aapcs_va_arg<'ll, 'tcx>(
     // if the offset >= 0 then the value will be on the stack
     let mut reg_off_v = bx.load(bx.type_i32(), reg_off, offset_align);
     let use_stack = bx.icmp(IntPredicate::IntSGE, reg_off_v, zero);
-    bx.cond_br(use_stack, on_stack.llbb(), maybe_reg.llbb());
+    bx.cond_br(use_stack, on_stack, maybe_reg);
 
     // The value at this point might be in a register, but there is a chance that
     // it could be on the stack so we have to update the offset and then check
     // the offset again.
 
+    bx.switch_to_block(maybe_reg);
     if gr_type && layout.align.abi.bytes() > 8 {
-        reg_off_v = maybe_reg.add(reg_off_v, bx.const_i32(15));
-        reg_off_v = maybe_reg.and(reg_off_v, bx.const_i32(-16));
+        reg_off_v = bx.add(reg_off_v, bx.const_i32(15));
+        reg_off_v = bx.and(reg_off_v, bx.const_i32(-16));
     }
-    let new_reg_off_v = maybe_reg.add(reg_off_v, bx.const_i32(slot_size as i32));
+    let new_reg_off_v = bx.add(reg_off_v, bx.const_i32(slot_size as i32));
 
-    maybe_reg.store(new_reg_off_v, reg_off, offset_align);
+    bx.store(new_reg_off_v, reg_off, offset_align);
 
     // Check to see if we have overflowed the registers as a result of this.
     // If we have then we need to use the stack for this value
-    let use_stack = maybe_reg.icmp(IntPredicate::IntSGT, new_reg_off_v, zero);
-    maybe_reg.cond_br(use_stack, on_stack.llbb(), in_reg.llbb());
+    let use_stack = bx.icmp(IntPredicate::IntSGT, new_reg_off_v, zero);
+    bx.cond_br(use_stack, on_stack, in_reg);
 
+    bx.switch_to_block(in_reg);
     let top_type = bx.type_i8p();
-    let top = in_reg.struct_gep(va_list_ty, va_list_addr, reg_top_index);
-    let top = in_reg.load(top_type, top, bx.tcx().data_layout.pointer_align.abi);
+    let top = bx.struct_gep(va_list_ty, va_list_addr, reg_top_index);
+    let top = bx.load(top_type, top, bx.tcx().data_layout.pointer_align.abi);
 
     // reg_value = *(@top + reg_off_v);
-    let mut reg_addr = in_reg.gep(bx.type_i8(), top, &[reg_off_v]);
+    let mut reg_addr = bx.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(bx.type_i8(), reg_addr, &[offset]);
+        reg_addr = bx.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));
-    let reg_value = in_reg.load(reg_type, reg_addr, layout.align.abi);
-    in_reg.br(end.llbb());
+    let reg_addr = bx.bitcast(reg_addr, bx.cx.type_ptr_to(reg_type));
+    let reg_value = bx.load(reg_type, reg_addr, layout.align.abi);
+    bx.br(end);
 
     // On Stack block
+    bx.switch_to_block(on_stack);
     let stack_value =
-        emit_ptr_va_arg(&mut on_stack, list, target_ty, false, Align::from_bytes(8).unwrap(), true);
-    on_stack.br(end.llbb());
+        emit_ptr_va_arg(bx, list, target_ty, false, Align::from_bytes(8).unwrap(), true);
+    bx.br(end);
 
-    let val = end.phi(
-        layout.immediate_llvm_type(bx),
-        &[reg_value, stack_value],
-        &[in_reg.llbb(), on_stack.llbb()],
-    );
+    bx.switch_to_block(end);
+    let val =
+        bx.phi(layout.immediate_llvm_type(bx), &[reg_value, stack_value], &[in_reg, on_stack]);
 
-    *bx = end;
     val
 }
 
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index fa390457674..f6c41af41b4 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -96,9 +96,10 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
 
             debug!("llblock: creating cleanup trampoline for {:?}", target);
             let name = &format!("{:?}_cleanup_trampoline_{:?}", self.bb, target);
-            let mut trampoline = fx.new_block(name);
-            trampoline.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
-            trampoline.llbb()
+            let trampoline = Bx::append_block(fx.cx, fx.llfn, name);
+            let mut trampoline_bx = Bx::build(fx.cx, trampoline);
+            trampoline_bx.cleanup_ret(self.funclet(fx).unwrap(), Some(lltarget));
+            trampoline
         } else {
             lltarget
         }
@@ -169,9 +170,9 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
             }
 
             if let Some((ret_dest, target)) = destination {
-                let mut ret_bx = fx.build_block(target);
-                fx.set_debug_loc(&mut ret_bx, self.terminator.source_info);
-                fx.store_return(&mut ret_bx, ret_dest, &fn_abi.ret, invokeret);
+                bx.switch_to_block(fx.llbb(target));
+                fx.set_debug_loc(bx, self.terminator.source_info);
+                fx.store_return(bx, ret_dest, &fn_abi.ret, invokeret);
             }
         } else {
             let llret = bx.call(fn_ty, fn_ptr, &llargs, self.funclet(fx));
@@ -452,15 +453,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
         // Create the failure block and the conditional branch to it.
         let lltarget = helper.llblock(self, target);
-        let panic_block = bx.build_sibling_block("panic");
+        let panic_block = bx.append_sibling_block("panic");
         if expected {
-            bx.cond_br(cond, lltarget, panic_block.llbb());
+            bx.cond_br(cond, lltarget, panic_block);
         } else {
-            bx.cond_br(cond, panic_block.llbb(), lltarget);
+            bx.cond_br(cond, panic_block, lltarget);
         }
 
         // After this point, bx is the block for the call to panic.
-        bx = panic_block;
+        bx.switch_to_block(panic_block);
         self.set_debug_loc(&mut bx, terminator.source_info);
 
         // Get the location information.
@@ -908,13 +909,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
             // Test whether the function pointer is associated with the type identifier.
             let cond = bx.type_test(fn_ptr, typeid_metadata);
-            let mut bx_pass = bx.build_sibling_block("type_test.pass");
-            let mut bx_fail = bx.build_sibling_block("type_test.fail");
-            bx.cond_br(cond, bx_pass.llbb(), bx_fail.llbb());
+            let bb_pass = bx.append_sibling_block("type_test.pass");
+            let bb_fail = bx.append_sibling_block("type_test.fail");
+            bx.cond_br(cond, bb_pass, bb_fail);
 
+            bx.switch_to_block(bb_pass);
             helper.do_call(
                 self,
-                &mut bx_pass,
+                &mut bx,
                 fn_abi,
                 fn_ptr,
                 &llargs,
@@ -922,8 +924,9 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 cleanup,
             );
 
-            bx_fail.abort();
-            bx_fail.unreachable();
+            bx.switch_to_block(bb_fail);
+            bx.abort();
+            bx.unreachable();
 
             return;
         }
@@ -1020,7 +1023,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     pub fn codegen_block(&mut self, bb: mir::BasicBlock) {
-        let mut bx = self.build_block(bb);
+        let llbb = self.llbb(bb);
+        let mut bx = Bx::build(self.cx, llbb);
         let mir = self.mir;
         let data = &mir[bb];
 
@@ -1356,16 +1360,20 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 //          bar();
                 //      }
                 Some(&mir::TerminatorKind::Abort) => {
-                    let mut cs_bx = self.new_block(&format!("cs_funclet{:?}", bb));
-                    let mut cp_bx = self.new_block(&format!("cp_funclet{:?}", bb));
-                    ret_llbb = cs_bx.llbb();
+                    let cs_bb =
+                        Bx::append_block(self.cx, self.llfn, &format!("cs_funclet{:?}", bb));
+                    let cp_bb =
+                        Bx::append_block(self.cx, self.llfn, &format!("cp_funclet{:?}", bb));
+                    ret_llbb = cs_bb;
 
-                    let cs = cs_bx.catch_switch(None, None, &[cp_bx.llbb()]);
+                    let mut cs_bx = Bx::build(self.cx, cs_bb);
+                    let cs = cs_bx.catch_switch(None, None, &[cp_bb]);
 
                     // The "null" here is actually a RTTI type descriptor for the
                     // C++ personality function, but `catch (...)` has no type so
                     // it's null. The 64 here is actually a bitfield which
                     // represents that this is a catch-all block.
+                    let mut cp_bx = Bx::build(self.cx, cp_bb);
                     let null = cp_bx.const_null(
                         cp_bx.type_i8p_ext(cp_bx.cx().data_layout().instruction_address_space),
                     );
@@ -1374,8 +1382,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     cp_bx.br(llbb);
                 }
                 _ => {
-                    let mut cleanup_bx = self.new_block(&format!("funclet_{:?}", bb));
-                    ret_llbb = cleanup_bx.llbb();
+                    let cleanup_bb =
+                        Bx::append_block(self.cx, self.llfn, &format!("funclet_{:?}", bb));
+                    ret_llbb = cleanup_bb;
+                    let mut cleanup_bx = Bx::build(self.cx, cleanup_bb);
                     funclet = cleanup_bx.cleanup_pad(None, &[]);
                     cleanup_bx.br(llbb);
                 }
@@ -1383,7 +1393,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             self.funclets[bb] = Some(funclet);
             ret_llbb
         } else {
-            let mut bx = self.new_block("cleanup");
+            let bb = Bx::append_block(self.cx, self.llfn, "cleanup");
+            let mut bx = Bx::build(self.cx, bb);
 
             let llpersonality = self.cx.eh_personality();
             let llretty = self.landing_pad_type();
@@ -1405,10 +1416,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
     fn unreachable_block(&mut self) -> Bx::BasicBlock {
         self.unreachable_block.unwrap_or_else(|| {
-            let mut bx = self.new_block("unreachable");
+            let llbb = Bx::append_block(self.cx, self.llfn, "unreachable");
+            let mut bx = Bx::build(self.cx, llbb);
             bx.unreachable();
-            self.unreachable_block = Some(bx.llbb());
-            bx.llbb()
+            self.unreachable_block = Some(llbb);
+            llbb
         })
     }
 
@@ -1416,7 +1428,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         self.double_unwind_guard.unwrap_or_else(|| {
             assert!(!base::wants_msvc_seh(self.cx.sess()));
 
-            let mut bx = self.new_block("abort");
+            let llbb = Bx::append_block(self.cx, self.llfn, "abort");
+            let mut bx = Bx::build(self.cx, llbb);
             self.set_debug_loc(&mut bx, mir::SourceInfo::outermost(self.mir.span));
 
             let llpersonality = self.cx.eh_personality();
@@ -1434,20 +1447,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             bx.apply_attrs_to_cleanup_callsite(llret);
 
             bx.unreachable();
-            let llbb = bx.llbb();
 
             self.double_unwind_guard = Some(llbb);
             llbb
         })
     }
 
-    // FIXME(eddyb) replace with `build_sibling_block`/`append_sibling_block`
-    // (which requires having a `Bx` already, and not all callers do).
-    fn new_block(&self, name: &str) -> Bx {
-        let llbb = Bx::append_block(self.cx, self.llfn, name);
-        Bx::build(self.cx, llbb)
-    }
-
     /// Get the backend `BasicBlock` for a MIR `BasicBlock`, either already
     /// cached in `self.cached_llbbs`, or created on demand (and cached).
     // FIXME(eddyb) rename `llbb` and other `ll`-prefixed things to use a
@@ -1461,11 +1466,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         })
     }
 
-    pub fn build_block(&mut self, bb: mir::BasicBlock) -> Bx {
-        let llbb = self.llbb(bb);
-        Bx::build(self.cx, llbb)
-    }
-
     fn make_return_dest(
         &mut self,
         bx: &mut Bx,
diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs
index 53fb21b269a..1c7fe060ea4 100644
--- a/compiler/rustc_codegen_ssa/src/traits/builder.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs
@@ -53,8 +53,7 @@ pub trait BuilderMethods<'a, 'tcx>:
 
     fn append_sibling_block(&mut self, name: &str) -> Self::BasicBlock;
 
-    // FIXME(eddyb) replace with callers using `append_sibling_block`.
-    fn build_sibling_block(&mut self, name: &str) -> Self;
+    fn switch_to_block(&mut self, llbb: Self::BasicBlock);
 
     fn ret_void(&mut self);
     fn ret(&mut self, v: Self::Value);