On Wed, Feb 03 2021, Ævar Arnfjörð Bjarmason wrote:

 void diffcore_pickaxe(struct diff_options *o)
 {
 	const char *needle = o->pickaxe;
 	int opts = o->pickaxe_opts;
-	regex_t regex, *regexp = NULL;
-	kwset_t kws = NULL;
+	struct grep_opt opt;
+
+	if (opts & (DIFF_PICKAXE_REGEX | DIFF_PICKAXE_KIND_GS_MASK)) {
+		grep_init(&opt, the_repository, NULL);
+#ifdef USE_LIBPCRE2
+		grep_commit_pattern_type(GREP_PATTERN_TYPE_PCRE, &opt);
+#else
+		grep_commit_pattern_type(GREP_PATTERN_TYPE_ERE, &opt);
+#endif
 
-	if (opts & (DIFF_PICKAXE_REGEX | DIFF_PICKAXE_KIND_G)) {
-		int cflags = REG_EXTENDED | REG_NEWLINE;
 		if (o->pickaxe_opts & DIFF_PICKAXE_IGNORE_CASE)
-			cflags |= REG_ICASE;
-		regcomp_or_die(&regex, needle, cflags);
-		regexp = &regex;
-	} else if (opts & DIFF_PICKAXE_KIND_S) {
-		if (o->pickaxe_opts & DIFF_PICKAXE_IGNORE_CASE &&
-		    has_non_ascii(needle)) {
-			struct strbuf sb = STRBUF_INIT;
-			int cflags = REG_NEWLINE | REG_ICASE;
-
-			basic_regex_quote_buf(&sb, needle);
-			regcomp_or_die(&regex, sb.buf, cflags);
-			strbuf_release(&sb);
-			regexp = &regex;
-		} else {
-			kws = kwsalloc(o->pickaxe_opts & DIFF_PICKAXE_IGNORE_CASE
-				       ? tolower_trans_tbl : NULL);
-			kwsincr(kws, needle, strlen(needle));
-			kwsprep(kws);
-		}
+			opt.ignore_case = 1;
+		if (opts & DIFF_PICKAXE_KIND_S &&
+		    !(opts & DIFF_PICKAXE_REGEX))
+			opt.fixed = 1;
+
+		append_grep_pattern(&opt, needle, "diffcore-pickaxe", 0, GREP_PATTERN);
+		compile_grep_patterns(&opt);
 	}
 
-	pickaxe(&diff_queued_diff, o, regexp, kws,
+	pickaxe(&diff_queued_diff, o, &opt,
 		(opts & DIFF_PICKAXE_KIND_G) ? diff_grep : has_changes);
 
-	if (regexp)
-		regfree(regexp);
-	if (kws)
-		kwsfree(kws);
+	if (opts & ~DIFF_PICKAXE_KIND_OBJFIND)
+		free_grep_patterns(&opt);
+
 	return;
 }

There's a bug here where now different things are dispatched to either
the -S or -G codepath wrongly, I've fixed it in my local version.

Anyway, it's interesting between this and the -U0 change that we have
little/no coverage for some/all of this. I'm trying to address that in
preceding patches in v2.