[CLANG] Resolves crash on invalid loop vectorize_width (#169473)

Diagnose malformed '#pragma clang loop vectorize_width' lists. Avoids
crash in HandlePragmaLoopHint, emit clear diagnostic and added
regression test.

Fixes #166325

Author: ebinjose02

clang/docs/ReleaseNotes.rst

@@ -783,6 +783,8 @@ Crash and bug fixes
 - Fixed a crash when compiling ``__real__`` or ``__imag__`` unary operator on scalar value with type promotion. (#GH160583)
 - Fixed a crash when parsing invalid nested name specifier sequences
   containing a single colon. (#GH167905)
+- Fixed a crash when parsing malformed #pragma clang loop vectorize_width(4,8,16)
+  by diagnosing invalid comma-separated argument lists. (#GH166325)
 
 Improvements
 ^^^^^^^^^^^^

clang/lib/Parse/ParsePragma.cpp

@@ -1531,7 +1531,7 @@ bool Parser::HandlePragmaLoopHint(LoopHint &Hint) {
         PP.Lex(Tok); // ,
 
         StateInfo = Tok.getIdentifierInfo();
-        IsScalableStr = StateInfo->getName();
+        IsScalableStr = StateInfo ? StateInfo->getName() : "";
 
         if (IsScalableStr != "scalable" && IsScalableStr != "fixed") {
           Diag(Tok.getLocation(),

clang/test/Parser/pragma-loop-vectorize.cpp

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only %s -verify
+
+void sum_vector(unsigned int A[], unsigned int B[], unsigned int sum[]) {
+  #pragma clang loop vectorize_width(4,8,16) vectorize(assume_safety)
+  // expected-error@-1 {{vectorize_width loop hint malformed; use vectorize_width(X, fixed) or vectorize_width(X, scalable) where X is an integer, or vectorize_width('fixed' or 'scalable')}}
+  // expected-warning@-2 {{extra tokens at end of '#pragma clang loop vectorize_width' - ignored}}
+
+  for (int k = 0; k < 64; k++) {
+    sum[k] = A[k] + 3 * B[k];
+  }
+}