[clang] [Clang] Allow the value of unroll count to be zero in `#pragma GCC unroll` and `#pragma unroll` (PR #88666)

[Erich Keane via cfe-commits]

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@@ -3903,7 +3904,14 @@ bool Sema::CheckLoopHintExpr(Expr *E, SourceLocation Loc) {
   if (R.isInvalid())
     return true;
 
-  bool ValueIsPositive = ValueAPS.isStrictlyPositive();
+  // GCC allows the value of unroll count to be 0.
+  // https://gcc.gnu.org/onlinedocs/gcc/Loop-Specific-Pragmas.html says
+  // "The values of 0 and 1 block any unrolling of the loop."
+  // The values doesn't have to be strictly positive in '#pragma GCC unroll' and
+  // '#pragma unroll' cases.
+  bool ValueIsPositive = PragmaNameInfo->isStr("unroll")
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erichkeane wrote:

Thanks!  I don't think we should do those changes in THIS patch, but I'd be ok with a followup patch to do that movement.

https://github.com/llvm/llvm-project/pull/88666