[clang] [OpenACC][CIR] Reduction combiner lowering for min/max (PR #163656)

[Erich Keane via cfe-commits]

================
@@ -3011,26 +3013,80 @@ bool SemaOpenACC::CreateReductionCombinerRecipe(
 
   assert(!VarTy->isArrayType() && "Only 1 level of array allowed");
 
+  enum class CombinerFailureKind {
+    None = 0,
+    BinOp = 1,
+    Conditional = 2,
+    Assignment = 3,
+  };
+
+  auto genCombiner = [&, this](DeclRefExpr *LHSDRE, DeclRefExpr *RHSDRE)
+      -> std::pair<ExprResult, CombinerFailureKind> {
+    ExprResult BinOpRes =
+        SemaRef.BuildBinOp(SemaRef.getCurScope(), Loc, BinOp, LHSDRE, RHSDRE,
+                           /*ForFoldExpr=*/false);
+    switch (ReductionOperator) {
+    case OpenACCReductionOperator::Addition:
+    case OpenACCReductionOperator::Multiplication:
+    case OpenACCReductionOperator::BitwiseAnd:
+    case OpenACCReductionOperator::BitwiseOr:
+    case OpenACCReductionOperator::BitwiseXOr:
+      // These 5 are simple and are being done  as compound operators, so we can
+      // immediately quit here.
+      return {BinOpRes, BinOpRes.isUsable() ? CombinerFailureKind::None
+                                            : CombinerFailureKind::BinOp};
+    case OpenACCReductionOperator::Max:
+    case OpenACCReductionOperator::Min: {
+      // These are done as:
+      // LHS = (LHS < RHS) ? LHS : RHS; and LHS = (LHS < RHS) ? RHS : LHS;
----------------
erichkeane wrote:

No, NaN isn't mentioned, just that I am allowed to use assignment and less-than for the purposes of this.  I suspect that NaN are just not noticed/cared about?

https://github.com/llvm/llvm-project/pull/163656