diff --git a/build.zig b/build.zig
index ed0fb0ffee..1af07ac296 100644
--- a/build.zig
+++ b/build.zig
@@ -1705,6 +1705,7 @@ fn addZig0TestStep(
         .root_source_file = b.path("stage0_test_root.zig"),
         .optimize = optimize,
         .target = target,
+        .valgrind = if (valgrind) true else null,
     });
     test_mod.addIncludePath(b.path("stage0"));
     test_mod.linkSystemLibrary("c", .{});
@@ -1735,6 +1736,7 @@ fn addZig0TestStep(
         .root_source_file = b.path("src/verbose_air.zig"),
         .target = target,
         .optimize = optimize,
+        .valgrind = if (valgrind) true else null,
     });
     dumper_mod.addImport("zig_internals", zig_internals_mod);
     dumper_mod.linkSystemLibrary("c", .{});
diff --git a/stage0/sema.c b/stage0/sema.c
index 5cddca6d8c..c349135567 100644
--- a/stage0/sema.c
+++ b/stage0/sema.c
@@ -192,7 +192,8 @@ static AirInstRef resolveInst(Sema* sema, ZirInstRef zir_ref) {
 // Appends an AIR instruction to sema's output arrays.
 // Returns the instruction index (not the ref).
 
-static uint32_t semaAddInstAsIndex(Sema* sema, AirInstTag inst_tag, AirInstData data) {
+static uint32_t semaAddInstAsIndex(
+    Sema* sema, AirInstTag inst_tag, AirInstData data) {
     if (sema->air_inst_len >= sema->air_inst_cap) {
         uint32_t new_cap = sema->air_inst_cap * 2;
         uint8_t* new_tags
@@ -588,7 +589,8 @@ static TypeIndex semaTypeOf(Sema* sema, AirInstRef ref) {
 
 // semaResolvePeerTypes: determine the common type of two AIR refs.
 // Ported from src/Sema.zig semaResolvePeerTypess (simplified).
-static TypeIndex semaResolvePeerTypes(Sema* sema, AirInstRef lhs, AirInstRef rhs) {
+static TypeIndex semaResolvePeerTypes(
+    Sema* sema, AirInstRef lhs, AirInstRef rhs) {
     TypeIndex lhs_ty = semaTypeOf(sema, lhs);
     TypeIndex rhs_ty = semaTypeOf(sema, rhs);
     if (lhs_ty == rhs_ty)
@@ -833,7 +835,7 @@ static AirInstRef zirBitCount(
         uint64_t result = 0;
         switch (air_tag) {
         case AIR_INST_CLZ:
-            if (uval == 0)
+            if (uval == 0 || bits == 0)
                 result = bits;
             else {
                 result = 0;
@@ -2699,8 +2701,7 @@ static AirInstRef zirCall(
                 memset(&data, 0, sizeof(data));
                 data.pl_op.operand = arg_refs[param_idx];
                 data.pl_op.payload = name_nts;
-                (void)semaAddInst(
-                    &child_block, AIR_INST_DBG_ARG_INLINE, data);
+                (void)semaAddInst(&child_block, AIR_INST_DBG_ARG_INLINE, data);
             }
             param_idx++;
         }
@@ -3540,7 +3541,8 @@ static AirInstRef semaResolveSwitchComptime(
             // debug undefined pattern.
             AirInstData block_data;
             memset(&block_data, 0xaa, sizeof(block_data));
-            uint32_t block_inst = semaAddInstAsIndex(sema, AIR_INST_BLOCK, block_data);
+            uint32_t block_inst
+                = semaAddInstAsIndex(sema, AIR_INST_BLOCK, block_data);
 
             // Set up a label so break can find this block.
             SemaBlockLabel label;
@@ -3594,7 +3596,8 @@ static AirInstRef semaResolveSwitchComptime(
         // Reserve BLOCK instruction (same as scalar case above).
         AirInstData block_data;
         memset(&block_data, 0xaa, sizeof(block_data));
-        uint32_t block_inst = semaAddInstAsIndex(sema, AIR_INST_BLOCK, block_data);
+        uint32_t block_inst
+            = semaAddInstAsIndex(sema, AIR_INST_BLOCK, block_data);
 
         SemaBlockLabel label;
         memset(&label, 0, sizeof(label));
@@ -4231,7 +4234,8 @@ static bool analyzeBodyInner(
                 memset(&br_data, 0, sizeof(br_data));
                 br_data.br.block_inst = blk_inst;
                 br_data.br.operand = AIR_REF_FROM_IP(IP_INDEX_VOID_VALUE);
-                uint32_t br_inst = semaAddInstAsIndex(sema, AIR_INST_BR, br_data);
+                uint32_t br_inst
+                    = semaAddInstAsIndex(sema, AIR_INST_BR, br_data);
 
                 // Write block extra: body_len2, then body insts.
                 uint32_t body_len2 = new_insts_count + 1; // +1 for BR
@@ -5153,10 +5157,11 @@ static bool analyzeBodyInner(
                                        - 1]
                             == AIR_REF_TO_INST(coerced));
                         uint32_t sub_bl = coerce_block.instructions_len + 1;
-                        uint32_t sub_br_idx = semaAddInstAsIndex(sema, AIR_INST_BR,
-                            (AirInstData) {
-                                .br = { .block_inst = label.merges.block_inst,
-                                    .operand = coerced } });
+                        uint32_t sub_br_idx
+                            = semaAddInstAsIndex(sema, AIR_INST_BR,
+                                (AirInstData) { .br
+                                    = { .block_inst = label.merges.block_inst,
+                                        .operand = coerced } });
                         uint32_t sub_extra = semaAddExtra(sema, sub_bl);
                         for (uint32_t si = 0;
                             si < coerce_block.instructions_len; si++) {