Simplify stack management by popping in bulk at higher levels

Since all memory used by the reader is POD in the stack, there is no benefit to
forcing code to explicitly pop everything pushed to the stack, since any
function can record an offset and pop back down to it regardless of what its
callers pushed if it knows that it does not need those items.

This is slightly more efficient (due to avoiding many pop calls), but also more
resilient since "leaks" at deeper levels of recursion get nuked by some caller
regardless of what was pushed.  This should help prevent future regressions
like f6437f606 (Fix memory consumption when reading documents).

1 files changed, 11 insertions, 23 deletions

diff --git a/src/stack.h b/src/stack.h
index e6e46372..4592705e 100644
--- a/src/stack.h
+++ b/src/stack.h
@@ -7,8 +7,8 @@
 #include <assert.h>
 #include <stdbool.h>
 #include <stddef.h>
-#include <stdint.h>
 #include <stdlib.h>
+#include <string.h>
 
 /** An offset to start the stack at. Note 0 is reserved for NULL. */
 #define SERD_STACK_BOTTOM sizeof(void*)
@@ -68,40 +68,28 @@ serd_stack_pop(SerdStack* stack, size_t n_bytes)
   stack->size -= n_bytes;
 }
 
+static inline void
+serd_stack_pop_to(SerdStack* stack, size_t n_bytes)
+{
+  assert(stack->size >= n_bytes);
+  stack->size = n_bytes;
+}
+
 static inline void*
 serd_stack_push_aligned(SerdStack* stack, size_t n_bytes, size_t align)
 {
-  // Push one byte to ensure space for a pad count
-  if (!serd_stack_push(stack, 1)) {
-    return NULL;
-  }
-
   // Push padding if necessary
   const size_t pad = align - stack->size % align;
   if (pad > 0) {
-    if (!serd_stack_push(stack, pad)) {
+    void* padding = serd_stack_push(stack, pad);
+    if (!padding) {
       return NULL;
     }
+    memset(padding, 0, pad);
   }
 
-  // Set top of stack to pad count so we can properly pop later
-  stack->buf[stack->size - 1] = (char)pad;
-
   // Push requested space at aligned location
   return serd_stack_push(stack, n_bytes);
 }
 
-static inline void
-serd_stack_pop_aligned(SerdStack* stack, size_t n_bytes)
-{
-  // Pop requested space down to aligned location
-  serd_stack_pop(stack, n_bytes);
-
-  // Get amount of padding from top of stack
-  const uint8_t pad = (uint8_t)stack->buf[stack->size - 1];
-
-  // Pop padding and pad count
-  serd_stack_pop(stack, pad + 1U);
-}
-
 #endif // SERD_SRC_STACK_H