Make blocks_per_json_file flag not output extra files (llvm#63)

Currently, the logic in convert_bhive_to_llvm_exegesis_input will create
extra (empty) files as the output at the end runs unconditionally rather
than when there are actually blocks to output. This means that if we
have a number of blocks that is an exact multiple of the value in
blocks_per_json_file, we end up getting no blocks after the loop, which
means we output an empty JSON file.

Fixes llvm#61.

Author: boomanaiden154

gematria/datasets/convert_bhive_to_llvm_exegesis_input.cc

@@ -346,7 +346,7 @@ int main(int argc, char* argv[]) {
     file_counter++;
   }
 
-  if (!json_output_dir.empty()) {
+  if (!json_output_dir.empty() && processed_snippets.size() != 0) {
     size_t json_file_number = file_counter / blocks_per_json_file;
     bool write_successfully = WriteJsonFile(std::move(processed_snippets),
                                             json_file_number, json_output_dir);

gematria/datasets/tests/blocks_per_json_file.test

@@ -1,52 +1,56 @@
 ; Test that splitting a dataset among multiple JSON files works as expected.
 
-; Test currently fails as underlying functionality needs to be fixed, see #61.
-; XFAIL: *
-
 ; RUN: split-file %s %t
 ; RUN: mkdir %t.jsondir
-; RUN: %convert_bhive_to_llvm_exegesis_input --json_output_dir=%t.jsondir --bhive_csv=%t/test.csv
+; RUN: %convert_bhive_to_llvm_exegesis_input --json_output_dir=%t.jsondir --bhive_csv=%t/test.csv --blocks_per_json_file=1
 ; RUN: cat %t.jsondir/0.json | FileCheck --check-prefix FILE1 %s
 ; RUN: cat %t.jsondir/1.json | FileCheck --check-prefix FILE2 %s
 
-; FILE1-CHECK: [
-; FILE1-CHECK:   {
-; FILE1-CHECK:     "Hex": "85c044897c2460",
-; FILE1-CHECK:     "MemoryDefinitions": [
-; FILE1-CHECK:       {
-; FILE1-CHECK:         "Name": "MEM",
-; FILE1-CHECK:         "Size": 4096,
-; FILE1-CHECK:         "Value": 305419776
-; FILE1-CHECK:       }
-; FILE1-CHECK:     ],
-; FILE1-CHECK:     "MemoryMappings": [
-; FILE1-CHECK:       {
-; FILE1-CHECK:         "Address": 65536,
-; FILE1-CHECK:         "Value": "MEM"
-; FILE1-CHECK:       }
-; FILE1-CHECK:     ]
-; FILE1-CHECK:   }
-; FILE1-CHECK: ]
+; Ensure that we don't have any "leftover" files.
+; RUN: ls %t.jsondir | FileCheck --check-prefix DIR %s
+
+; FILE1: [
+; FILE1:   {
+; FILE1:     "Hex": "85c044897c2460",
+; FILE1:     "MemoryDefinitions": [
+; FILE1:       {
+; FILE1:         "Name": "MEM",
+; FILE1:         "Size": 4096,
+; FILE1:         "Value": 305419776
+; FILE1:       }
+; FILE1:     ],
+; FILE1:     "MemoryMappings": [
+; FILE1:       {
+; FILE1:         "Address": 65536,
+; FILE1:         "Value": "MEM"
+; FILE1:       }
+; FILE1:     ]
+; FILE1:   }
+; FILE1: ]
+
+; FILE2: [
+; FILE2:   {
+; FILE2:     "Hex": "3b31",
+; FILE2:     "MemoryDefinitions": [
+; FILE2:       {
+; FILE2:         "Name": "MEM",
+; FILE2:         "Size": 4096,
+; FILE2:         "Value": 305419776
+; FILE2:       }
+; FILE2:     ],
+; FILE2:     "MemoryMappings": [
+; FILE2:       {
+; FILE2:         "Address": 65536,
+; FILE2:         "Value": "MEM"
+; FILE2:       }
+; FILE2:     ]
+; FILE2:   }
+; FILE2: ]
 
-; FILE2-CHECK: [
-; FILE2-CHECK:   {
-; FILE2-CHECK:     "Hex": "3b31",
-; FILE2-CHECK:     "MemoryDefinitions": [
-; FILE2-CHECK:       {
-; FILE2-CHECK:         "Name": "MEM",
-; FILE2-CHECK:         "Size": 4096,
-; FILE2-CHECK:         "Value": 305419776
-; FILE2-CHECK:       }
-; FILE2-CHECK:     ],
-; FILE2-CHECK:     "MemoryMappings": [
-; FILE2-CHECK:       {
-; FILE2-CHECK:         "Address": 65536,
-; FILE2-CHECK:         "Value": "MEM"
-; FILE2-CHECK:       }
-; FILE2-CHECK:     ]
-; FILE2-CHECK:   }
-; FILE2-CHECK: ]
+; DIR: 0.json
+; DIR: 1.json
+; DIR-NOT: 2.json
 
 ;--- test.csv
-3b31,45.000000
 85c044897c2460,98.000000
+3b31,45.000000