gccrs: prealloc the initilizer vector

There are two cases when initilizing an array, this is the
const context which means we need to build the array ctor,
which means using lots of memory, its super inefficient
because we are using a big wrapper over the GCC internals here
but preallocating the vectors here causes a:

  terminate called after throwing an instance of 'std::bad_alloc'

So this is a handy error condition to rely on for this senario.

Fixes Rust-GCC#3713
Fixes Rust-GCC#3727

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::array_copied_expr): prealloc the vector

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

diff --git a/gcc/rust/backend/rust-compile-expr.cc b/gcc/rust/backend/rust-compile-expr.cc
index 1e09c6c155ae1f380025ee478f8941b1039a1b69..339317d81747c35ebf11d09b9342a523c5b0178b 100644 (file)
--- a/gcc/rust/backend/rust-compile-expr.cc
+++ b/gcc/rust/backend/rust-compile-expr.cc
@@ -1972,8 +1972,12 @@ CompileExpr::array_copied_expr (location_t expr_locus,
   if (ctx->const_context_p ())
     {
       size_t idx = 0;
+
       std::vector<unsigned long> indexes;
       std::vector<tree> constructor;
+
+      indexes.reserve (len);
+      constructor.reserve (len);
       for (unsigned HOST_WIDE_INT i = 0; i < len; i++)
        {
          constructor.push_back (translated_expr);