[clang] [CIR] Upstream lowering of conditional operators to TernaryOp (PR #138156)

[Morris Hafner via cfe-commits]

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@@ -948,6 +950,165 @@ void CIRGenFunction::emitIgnoredExpr(const Expr *e) {
   emitLValue(e);
 }
 
+// Handle the case where the condition is a constant evaluatable simple integer,
+// which means we don't have to separately handle the true/false blocks.
+static std::optional<LValue> handleConditionalOperatorLValueSimpleCase(
+    CIRGenFunction &cgf, const AbstractConditionalOperator *e) {
+  const Expr *condExpr = e->getCond();
+  bool condExprBool;
+  if (cgf.constantFoldsToSimpleInteger(condExpr, condExprBool)) {
+    const Expr *live = e->getTrueExpr(), *dead = e->getFalseExpr();
+    if (!condExprBool)
+      std::swap(live, dead);
+
+    if (!cgf.containsLabel(dead)) {
+      // If the true case is live, we need to track its region.
+      if (condExprBool) {
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mmha wrote:

I don't know much about PGO, but from what I gather this code is correct. Clang/LLVM optimize branch coverage by only emitting counters for true branches. The false branch count is then calculated with `parent_count - true_count` See slide 12 [here](https://llvm.org/devmtg/2020-09/slides/PhippsAlan_BranchCoverage_LLVM_Conf_Talk_final.pdf). It the condition is always false there's no counter to increment.

https://github.com/llvm/llvm-project/pull/138156