[PUSHED] Avoid SIGSEGV in nvptx 'mkoffload' for voluminous PTX code

[Thomas Schwinge]

In commit 50be486dff4ea2676ed022e9524ef190b92ae2b1
"nvptx: libgomp+mkoffload.cc: Prepare for reverse offload fn lookup", some
additional tracking of the PTX code was added, and this assumes that
potentially every single character of PTX code needs to be tracked as a new
chunk of PTX code.  That's problematic if we're dealing with voluminous PTX
code (for example, non-trivial C++ code), and the 'file_idx' 'alloca'tion then
causes stack overflow.  For example:

    FAIL: libgomp.c++/target-std__valarray-1.C (test for excess errors)
    UNRESOLVED: libgomp.c++/target-std__valarray-1.C compilation failed to 
produce executable

    lto-wrapper: fatal error: [...]/build-gcc/gcc//accel/nvptx-none/mkoffload 
terminated with signal 11 [Segmentation fault], core dumped

        gcc/
        * config/nvptx/mkoffload.cc (process): Use an 'auto_vec' for
        'file_idx'.
---
 gcc/config/nvptx/mkoffload.cc | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/gcc/config/nvptx/mkoffload.cc b/gcc/config/nvptx/mkoffload.cc
index e7ec0ef4f6a..bb3f0fcee6b 100644
--- a/gcc/config/nvptx/mkoffload.cc
+++ b/gcc/config/nvptx/mkoffload.cc
@@ -260,8 +260,10 @@ process (FILE *in, FILE *out, uint32_t omp_requires)
   unsigned ix;
   const char *sm_ver = NULL, *version = NULL;
   const char *sm_ver2 = NULL, *version2 = NULL;
-  size_t file_cnt = 0;
-  size_t *file_idx = XALLOCAVEC (size_t, len);
+  /* To reduce the number of reallocations for 'file_idx', guess 'file_cnt'
+     (very roughly...), based on 'len'.  */
+  const size_t file_cnt_guessed = 13 + len / 27720;
+  auto_vec<size_t> file_idx (file_cnt_guessed);
 
   fprintf (out, "#include <stdint.h>\n\n");
 
@@ -269,9 +271,10 @@ process (FILE *in, FILE *out, uint32_t omp_requires)
      terminated by a NUL.  */
   for (size_t i = 0; i != len;)
     {
+      file_idx.safe_push (i);
+
       char c;
       bool output_fn_ptr = false;
-      file_idx[file_cnt++] = i;
 
       fprintf (out, "static const char ptx_code_%u[] =\n\t\"", obj_count++);
       while ((c = input[i++]))
@@ -349,6 +352,9 @@ process (FILE *in, FILE *out, uint32_t omp_requires)
        }
     }
 
+  const size_t file_cnt = file_idx.length ();
+  gcc_checking_assert (file_cnt == obj_count);
+
   /* Create function-pointer array, required for reverse
      offload function-pointer lookup.  */
 
-- 
2.34.1