Commit 4f8c26d2c6

@@ -1389,7 +1389,7 @@ static void resolve_enum_type(CodeGen *g, TypeTableEntry *enum_type) {
         return;
     }
 
-    TypeTableEntry *tag_int_type = get_smallest_unsigned_int_type(g, field_count);
+    TypeTableEntry *tag_int_type = get_smallest_unsigned_int_type(g, field_count - 1);
     TypeTableEntry *tag_type_entry = create_enum_tag_type(g, enum_type, tag_int_type);
     enum_type->data.enumeration.tag_type = tag_type_entry;
 

@@ -2666,9 +2666,16 @@ static LLVMValueRef ir_render_enum_tag_name(CodeGen *g, IrExecutable *executable
     if (ir_want_debug_safety(g, &instruction->base)) {
         TypeTableEntry *enum_type = enum_tag_type->data.enum_tag.enum_type;
         size_t field_count = enum_type->data.enumeration.src_field_count;
-        LLVMValueRef zero = LLVMConstNull(LLVMTypeOf(enum_tag_value));
-        LLVMValueRef end_val = LLVMConstInt(LLVMTypeOf(enum_tag_value), field_count, false);
-        add_bounds_check(g, enum_tag_value, LLVMIntUGE, zero, LLVMIntULT, end_val);
+
+        // if the field_count can't fit in the bits of the enum_tag_type, then it can't possibly
+        // be the wrong value
+        BigInt field_bi;
+        bigint_init_unsigned(&field_bi, field_count);
+        TypeTableEntry *tag_int_type = enum_tag_type->data.enum_tag.int_type;
+        if (bigint_fits_in_bits(&field_bi, tag_int_type->data.integral.bit_count, false)) {
+            LLVMValueRef end_val = LLVMConstInt(LLVMTypeOf(enum_tag_value), field_count, false);
+            add_bounds_check(g, enum_tag_value, LLVMIntEQ, nullptr, LLVMIntULT, end_val);
+        }
     }
 
     LLVMValueRef indices[] = {

@@ -136,3 +136,57 @@ const AlignTestEnum = enum {
     A: [9]u8,
     B: u64,
 };
+
+const ValueCount0 = enum {};
+const ValueCount1 = enum { I0 };
+const ValueCount2 = enum { I0, I1 };
+const ValueCount256 = enum {
+    I0, I1, I2, I3, I4, I5, I6, I7, I8, I9, I10, I11, I12, I13, I14, I15,
+    I16, I17, I18, I19, I20, I21, I22, I23, I24, I25, I26, I27, I28, I29, I30, I31,
+    I32, I33, I34, I35, I36, I37, I38, I39, I40, I41, I42, I43, I44, I45, I46, I47,
+    I48, I49, I50, I51, I52, I53, I54, I55, I56, I57, I58, I59, I60, I61, I62, I63,
+    I64, I65, I66, I67, I68, I69, I70, I71, I72, I73, I74, I75, I76, I77, I78, I79,
+    I80, I81, I82, I83, I84, I85, I86, I87, I88, I89, I90, I91, I92, I93, I94, I95,
+    I96, I97, I98, I99, I100, I101, I102, I103, I104, I105, I106, I107, I108, I109,
+    I110, I111, I112, I113, I114, I115, I116, I117, I118, I119, I120, I121, I122, I123,
+    I124, I125, I126, I127, I128, I129, I130, I131, I132, I133, I134, I135, I136, I137,
+    I138, I139, I140, I141, I142, I143, I144, I145, I146, I147, I148, I149, I150, I151,
+    I152, I153, I154, I155, I156, I157, I158, I159, I160, I161, I162, I163, I164, I165,
+    I166, I167, I168, I169, I170, I171, I172, I173, I174, I175, I176, I177, I178, I179,
+    I180, I181, I182, I183, I184, I185, I186, I187, I188, I189, I190, I191, I192, I193,
+    I194, I195, I196, I197, I198, I199, I200, I201, I202, I203, I204, I205, I206, I207,
+    I208, I209, I210, I211, I212, I213, I214, I215, I216, I217, I218, I219, I220, I221,
+    I222, I223, I224, I225, I226, I227, I228, I229, I230, I231, I232, I233, I234, I235,
+    I236, I237, I238, I239, I240, I241, I242, I243, I244, I245, I246, I247, I248, I249,
+    I250, I251, I252, I253, I254, I255
+};
+const ValueCount257 = enum {
+    I0, I1, I2, I3, I4, I5, I6, I7, I8, I9, I10, I11, I12, I13, I14, I15,
+    I16, I17, I18, I19, I20, I21, I22, I23, I24, I25, I26, I27, I28, I29, I30, I31,
+    I32, I33, I34, I35, I36, I37, I38, I39, I40, I41, I42, I43, I44, I45, I46, I47,
+    I48, I49, I50, I51, I52, I53, I54, I55, I56, I57, I58, I59, I60, I61, I62, I63,
+    I64, I65, I66, I67, I68, I69, I70, I71, I72, I73, I74, I75, I76, I77, I78, I79,
+    I80, I81, I82, I83, I84, I85, I86, I87, I88, I89, I90, I91, I92, I93, I94, I95,
+    I96, I97, I98, I99, I100, I101, I102, I103, I104, I105, I106, I107, I108, I109,
+    I110, I111, I112, I113, I114, I115, I116, I117, I118, I119, I120, I121, I122, I123,
+    I124, I125, I126, I127, I128, I129, I130, I131, I132, I133, I134, I135, I136, I137,
+    I138, I139, I140, I141, I142, I143, I144, I145, I146, I147, I148, I149, I150, I151,
+    I152, I153, I154, I155, I156, I157, I158, I159, I160, I161, I162, I163, I164, I165,
+    I166, I167, I168, I169, I170, I171, I172, I173, I174, I175, I176, I177, I178, I179,
+    I180, I181, I182, I183, I184, I185, I186, I187, I188, I189, I190, I191, I192, I193,
+    I194, I195, I196, I197, I198, I199, I200, I201, I202, I203, I204, I205, I206, I207,
+    I208, I209, I210, I211, I212, I213, I214, I215, I216, I217, I218, I219, I220, I221,
+    I222, I223, I224, I225, I226, I227, I228, I229, I230, I231, I232, I233, I234, I235,
+    I236, I237, I238, I239, I240, I241, I242, I243, I244, I245, I246, I247, I248, I249,
+    I250, I251, I252, I253, I254, I255, I256
+};
+
+test "enum sizes" {
+    comptime {
+        assert(@sizeOf(ValueCount0) == 0);
+        assert(@sizeOf(ValueCount1) == 0);
+        assert(@sizeOf(ValueCount2) == 1);
+        assert(@sizeOf(ValueCount256) == 1);
+        assert(@sizeOf(ValueCount257) == 2);
+    }
+}