Fix static analysis findings: uninitialized vars, bitwise shift UB, garbage values

- nla_core.cpp: Initialize j = null_lpvar in is_octagon_term
- bit2int.cpp: Initialize sign_p, sign_n, sz_p, sz_n
- act_cache.cpp: Initialize debug vars to nullptr
- enum2bv_rewriter.cpp: Use unsigned literal in 1u << idx
- bit_matrix.cpp: Use unsigned literal in 1u << (n-1)
- bit_util.cpp: Guard against bit_shift == 0 in shl/shr
- mpff.cpp: Cast exp to unsigned before shifting
- sorting_network.h: Guard against bits == 0
- dl_sparse_table.h: Use >= 64 instead of == 64

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

src/util/bit_util.cpp

@@ -214,6 +214,15 @@ void shl(std::span<unsigned const> src, unsigned k, std::span<unsigned> dst) {
         }
     }
     else {
+        if (bit_shift == 0) {
+            if (src_sz > dst_sz)
+                src_sz = dst_sz;
+            for (size_t i = 0; i < src_sz; ++i)
+                dst[i] = src[i];
+            for (size_t i = src_sz; i < dst_sz; ++i)
+                dst[i] = 0;
+            return;
+        }
         unsigned comp_shift = (8 * sizeof(unsigned)) - bit_shift;
         unsigned prev       = 0;
         if (src_sz > dst_sz)
@@ -278,7 +287,11 @@ void shr(std::span<unsigned const> src, unsigned k, std::span<unsigned> dst) {
         }
         else {
             SASSERT(new_sz == sz);
-            SASSERT(bit_shift != 0);
+            if (bit_shift == 0) {
+                for (size_t i = 0; i < sz; ++i)
+                    dst[i] = src[i];
+                return;
+            }
             unsigned i       = 0;
             for (; i < new_sz - 1; ++i) {
                 dst[i] = src[i];
@@ -327,20 +340,26 @@ void shr(std::span<unsigned const> src, unsigned k, std::span<unsigned> dst) {
     }
     else {
         SASSERT(new_sz == src_sz);
-        SASSERT(bit_shift != 0);
-        auto sz = new_sz;
-        if (new_sz > dst_sz)
-            sz = dst_sz;
-        unsigned i       = 0;
-        for (; i < sz - 1; ++i) {
+        if (bit_shift == 0) {
+            auto sz = std::min(new_sz, dst_sz);
+            for (size_t i = 0; i < sz; ++i)
+                dst[i] = src[i];
+        }
+        else {
+            auto sz = new_sz;
+            if (new_sz > dst_sz)
+                sz = dst_sz;
+            unsigned i       = 0;
+            for (; i < sz - 1; ++i) {
+                dst[i] = src[i];
+                dst[i] >>= bit_shift;
+                dst[i] |= (src[i+1] << comp_shift);
+            }
             dst[i] = src[i];
             dst[i] >>= bit_shift;
-            dst[i] |= (src[i+1] << comp_shift);
+            if (new_sz > dst_sz)
+                dst[i] |= (src[i+1] << comp_shift);
         }
-        dst[i] = src[i];
-        dst[i] >>= bit_shift;
-        if (new_sz > dst_sz)
-            dst[i] |= (src[i+1] << comp_shift);
     }
     for (auto i = new_sz; i < dst_sz; ++i)
         dst[i] = 0;

src/util/mpff.cpp

@@ -161,7 +161,7 @@ uint64_t mpff_manager::get_uint64(mpff const & a) const {
     int exp = -a.m_exponent - sizeof(unsigned) * 8 * (m_precision - 2);
     SASSERT(exp >= 0);
     uint64_t * s = reinterpret_cast<uint64_t*>(sig(a) + (m_precision - 2));
-    return *s >> exp;
+    return *s >> static_cast<unsigned>(exp);
 }
 
 int64_t mpff_manager::get_int64(mpff const & a) const {
@@ -175,7 +175,7 @@ int64_t mpff_manager::get_int64(mpff const & a) const {
         return INT64_MIN;
     }
     else {
-        int64_t r = *s >> exp;
+        int64_t r = *s >> static_cast<unsigned>(exp);
         if (is_neg(a))
             r = -r;
         return r;

src/util/sorting_network.h

@@ -412,7 +412,7 @@ Notes:
                 bits++;
                 w_max >>= 1;
             }
-            unsigned pow = (1ul << (bits-1));
+            unsigned pow = bits > 0 ? (1u << (bits-1)) : 0;
             unsigned a = (k + pow - 1) / pow; // a*pow >= k
             SASSERT(a*pow >= k);
             SASSERT((a-1)*pow < k);