copy elision: if bool expression with aggregate

```zig
export fn entry() void {
    var y = true;
    var z = bar();
    var x = if (y) foo() else z;
}
```

```llvm
define void @entry() #2 !dbg !41 {
Entry:
  %y = alloca i1, align 1
  %z = alloca %Foo, align 4
  %x = alloca %Foo, align 4
  store i1 true, i1* %y, align 1, !dbg !57
  call void @llvm.dbg.declare(metadata i1* %y, metadata !45, metadata !DIExpression()), !dbg !58
  call fastcc void @bar(%Foo* sret %z), !dbg !59
  call void @llvm.dbg.declare(metadata %Foo* %z, metadata !48, metadata !DIExpression()), !dbg !60
  %0 = load i1, i1* %y, align 1, !dbg !61
  br i1 %0, label %Then, label %Else, !dbg !61

Then:                                             ; preds = %Entry
  call fastcc void @foo(%Foo* sret %x), !dbg !62
  br label %EndIf, !dbg !63

Else:                                             ; preds = %Entry
  %1 = bitcast %Foo* %z to i8*, !dbg !64
  %2 = bitcast %Foo* %x to i8*, !dbg !64
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 4 %2, i8* align 4 %1, i64 8, i1 false), !dbg !64
  br label %EndIf, !dbg !63

EndIf:                                            ; preds = %Else, %Then
  call void @llvm.dbg.declare(metadata %Foo* %x, metadata !55, metadata !DIExpression()), !dbg !65
  ret void, !dbg !66
}
```

Author: andrewrk

Diff for: src/all_types.hpp

@@ -2184,6 +2184,7 @@ enum IrInstructionId {
     IrInstructionIdStoreResult,
     IrInstructionIdAllocaSrc,
     IrInstructionIdAllocaGen,
+    IrInstructionIdAssertNonError,
 };
 
 struct IrInstruction {
@@ -2338,6 +2339,7 @@ struct IrInstructionLoadPtr {
     IrInstruction base;
 
     IrInstruction *ptr;
+    IrInstruction *result_loc;
 };
 
 struct IrInstructionStorePtr {
@@ -3011,6 +3013,8 @@ struct IrInstructionTypeName {
 enum LVal {
     LValNone,
     LValPtr,
+    LValErrorUnion,
+    LValOptional,
 };
 
 struct IrInstructionDeclRef {
@@ -3346,6 +3350,12 @@ struct IrInstructionAllocaGen {
     const char *name_hint;
 };
 
+struct IrInstructionAssertNonError {
+    IrInstruction base;
+
+    IrInstruction *err_code;
+};
+
 static const size_t slice_ptr_index = 0;
 static const size_t slice_len_index = 1;
 

Diff for: src/codegen.cpp

@@ -5108,6 +5108,26 @@ static LLVMValueRef ir_render_result_optional_payload(CodeGen *g, IrExecutable *
     return LLVMBuildStructGEP(g->builder, prev_result_loc, maybe_child_index, "");
 }
 
+static LLVMValueRef ir_render_assert_non_error(CodeGen *g, IrExecutable *executable,
+        IrInstructionAssertNonError *instruction)
+{
+    if (!ir_want_runtime_safety(g, &instruction->base) || g->errors_by_index.length <= 1) {
+        return nullptr;
+    }
+    LLVMValueRef err_val = ir_llvm_value(g, instruction->err_code);
+    LLVMValueRef zero = LLVMConstNull(g->err_tag_type->type_ref);
+    LLVMValueRef cond_val = LLVMBuildICmp(g->builder, LLVMIntEQ, err_val, zero, "");
+    LLVMBasicBlockRef err_block = LLVMAppendBasicBlock(g->cur_fn_val, "UnwrapErrError");
+    LLVMBasicBlockRef ok_block = LLVMAppendBasicBlock(g->cur_fn_val, "UnwrapErrOk");
+    LLVMBuildCondBr(g->builder, cond_val, ok_block, err_block);
+
+    LLVMPositionBuilderAtEnd(g->builder, err_block);
+    gen_safety_crash_for_err(g, err_val, instruction->base.scope);
+
+    LLVMPositionBuilderAtEnd(g->builder, ok_block);
+    return nullptr;
+}
+
 static void set_debug_location(CodeGen *g, IrInstruction *instruction) {
     AstNode *source_node = instruction->source_node;
     Scope *scope = instruction->scope;
@@ -5351,6 +5371,8 @@ static LLVMValueRef ir_render_instruction(CodeGen *g, IrExecutable *executable,
             return ir_render_result_return(g, executable, (IrInstructionResultReturn *)instruction);
         case IrInstructionIdResultOptionalPayload:
             return ir_render_result_optional_payload(g, executable, (IrInstructionResultOptionalPayload *)instruction);
+        case IrInstructionIdAssertNonError:
+            return ir_render_assert_non_error(g, executable, (IrInstructionAssertNonError *)instruction);
         case IrInstructionIdResultErrorUnionPayload:
             zig_panic("TODO");
         case IrInstructionIdResultSliceToBytes: