From 66b2477ab668447c6cbff68770de14ec8db991be Mon Sep 17 00:00:00 2001
From: xackus <14938807+xackus@users.noreply.github.com>
Date: Mon, 6 Apr 2020 09:44:06 +0200
Subject: [PATCH] fix lazy value in ir_analyze_instruction_elem_ptr

---
 src/ir.cpp                         | 6 +++++-
 test/stage1/behavior.zig           | 1 +
 test/stage1/behavior/bugs/4954.zig | 8 ++++++++
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 test/stage1/behavior/bugs/4954.zig

diff --git a/src/ir.cpp b/src/ir.cpp
index b570117177..bcadc89243 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -21149,7 +21149,11 @@ static IrInstGen *ir_analyze_instruction_elem_ptr(IrAnalyze *ira, IrInstSrcElemP
 
     bool safety_check_on = elem_ptr_instruction->safety_check_on;
     if (instr_is_comptime(casted_elem_index)) {
-        uint64_t index = bigint_as_u64(&casted_elem_index->value->data.x_bigint);
+        ZigValue *index_val = ir_resolve_const(ira, casted_elem_index, UndefBad);
+        if (index_val == nullptr)
+            return ira->codegen->invalid_inst_gen;
+        uint64_t index = bigint_as_u64(&index_val->data.x_bigint);
+
         if (array_type->id == ZigTypeIdArray) {
             uint64_t array_len = array_type->data.array.len +
                 (array_type->data.array.sentinel != nullptr);
diff --git a/test/stage1/behavior.zig b/test/stage1/behavior.zig
index 52ce5979e1..61b0c1aa56 100644
--- a/test/stage1/behavior.zig
+++ b/test/stage1/behavior.zig
@@ -44,6 +44,7 @@ comptime {
     _ = @import("behavior/bugs/4769_a.zig");
     _ = @import("behavior/bugs/4769_b.zig");
     _ = @import("behavior/bugs/4769_c.zig");
+    _ = @import("behavior/bugs/4954.zig");
     _ = @import("behavior/bugs/394.zig");
     _ = @import("behavior/bugs/421.zig");
     _ = @import("behavior/bugs/529.zig");
diff --git a/test/stage1/behavior/bugs/4954.zig b/test/stage1/behavior/bugs/4954.zig
new file mode 100644
index 0000000000..b5a9bdf851
--- /dev/null
+++ b/test/stage1/behavior/bugs/4954.zig
@@ -0,0 +1,8 @@
+fn f(buf: []u8) void {
+    var ptr = &buf[@sizeOf(u32)];
+}
+
+test "crash" {
+    var buf: [4096]u8 = undefined;
+    f(&buf);
+}