Bug in llvm/utils/print-before-all.py script, fails to compile chunk-0.ll

[knaumov]

Summary

Prior to the fix, the script was not annotating the first line of chunk-0.ll. Because of that, a compilation with bin/opt was failing.

The script takes the output of ./bin/opt with the flag -print-before-all and chunks it into the separate files by passes. It has a buffer and if it is not zero and the line starts with "*** IR Dump Before", then it is being printed with the annotation (";") to the first line. This logic is missing the very first chunk (chunk-0.ll) and skips it during the annotation as the buffer is empty at this time.
While all the chunk files but the first one would have this written on the top:

; ***IR Dump Before <name of the pass>
....

The first file would not have this line annotated properly:

***IR Dump Before <name of the pass>
....

This creates compilation errors with ./bin/opt .
The extra if-statement ensures that the corner case is covered

[knaumov]

Ping

[apilipenko]

Can you please elaborate what is the issue you are solving? May be give an example?

It's not very clear to me from the description of the patch.

llvm/utils/chunk-print-before-all.py

def print_chunk(lines):
     chunk_id = chunk_id + 1
     print("writing chunk " + fname + " (" + str(len(lines)) + " lines)")
     with open(fname, "w") as f:
         f.writelines(lines)
 
 is_dump = False
 cur = []
 for line in sys.stdin:
-    if line.startswith("*** IR Dump Before ") and len(cur) != 0:
+    if line.startswith("*** IR Dump Before "):
+        if len(cur) != 0:
             print_chunk(cur);
             cur = []
         cur.append("; " + line)
     elif line.startswith("Stack dump:"):
         print_chunk(cur);
         cur = []
         cur.append(line)
         is_dump = True
     else:
         cur.append(line)
 
 if is_dump:
     print("writing crashinfo.txt (" + str(len(cur)) + " lines)")
     with open("crashinfo.txt", "w") as f:
         f.writelines(cur)
 else:
     print_chunk(cur);