Implement p0292r2 (constexpr if), a likely C++1z feature.

llvm-svn: 273602

3 files changed, 15 insertions, 10 deletions

diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index ff70bbc866f..9a93fce7b00 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -563,7 +563,8 @@ void CodeGenFunction::EmitIfStmt(const IfStmt &S) {
   // If the condition constant folds and can be elided, try to avoid emitting
   // the condition and the dead arm of the if/else.
   bool CondConstant;
-  if (ConstantFoldsToSimpleInteger(S.getCond(), CondConstant)) {
+  if (ConstantFoldsToSimpleInteger(S.getCond(), CondConstant,
+                                   S.isConstexpr())) {
     // Figure out which block (then or else) is executed.
     const Stmt *Executed = S.getThen();
     const Stmt *Skipped  = S.getElse();
@@ -572,7 +573,7 @@ void CodeGenFunction::EmitIfStmt(const IfStmt &S) {
 
     // If the skipped block has no labels in it, just emit the executed block.
     // This avoids emitting dead code and simplifies the CFG substantially.
-    if (!ContainsLabel(Skipped)) {
+    if (S.isConstexpr() || !ContainsLabel(Skipped)) {
       if (CondConstant)
         incrementProfileCounter(&S);
       if (Executed) {
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 1d46eea45fd..2dc4c12ce2e 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1107,9 +1107,10 @@ bool CodeGenFunction::containsBreak(const Stmt *S) {
 /// to a constant, or if it does but contains a label, return false.  If it
 /// constant folds return true and set the boolean result in Result.
 bool CodeGenFunction::ConstantFoldsToSimpleInteger(const Expr *Cond,
-                                                   bool &ResultBool) {
+                                                   bool &ResultBool,
+                                                   bool AllowLabels) {
   llvm::APSInt ResultInt;
-  if (!ConstantFoldsToSimpleInteger(Cond, ResultInt))
+  if (!ConstantFoldsToSimpleInteger(Cond, ResultInt, AllowLabels))
     return false;
 
   ResultBool = ResultInt.getBoolValue();
@@ -1119,15 +1120,16 @@ bool CodeGenFunction::ConstantFoldsToSimpleInteger(const Expr *Cond,
 /// ConstantFoldsToSimpleInteger - If the specified expression does not fold
 /// to a constant, or if it does but contains a label, return false.  If it
 /// constant folds return true and set the folded value.
-bool CodeGenFunction::
-ConstantFoldsToSimpleInteger(const Expr *Cond, llvm::APSInt &ResultInt) {
+bool CodeGenFunction::ConstantFoldsToSimpleInteger(const Expr *Cond,
+                                                   llvm::APSInt &ResultInt,
+                                                   bool AllowLabels) {
   // FIXME: Rename and handle conversion of other evaluatable things
   // to bool.
   llvm::APSInt Int;
   if (!Cond->EvaluateAsInt(Int, getContext()))
     return false;  // Not foldable, not integer or not fully evaluatable.
 
-  if (CodeGenFunction::ContainsLabel(Cond))
+  if (!AllowLabels && CodeGenFunction::ContainsLabel(Cond))
     return false;  // Contains a label.
 
   ResultInt = Int;
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index b96e6bad8a1..af7e6114af6 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -3051,13 +3051,15 @@ public:
   /// ConstantFoldsToSimpleInteger - If the specified expression does not fold
   /// to a constant, or if it does but contains a label, return false.  If it
   /// constant folds return true and set the boolean result in Result.
-  bool ConstantFoldsToSimpleInteger(const Expr *Cond, bool &Result);
+  bool ConstantFoldsToSimpleInteger(const Expr *Cond, bool &Result,
+                                    bool AllowLabels = false);
 
   /// ConstantFoldsToSimpleInteger - If the specified expression does not fold
   /// to a constant, or if it does but contains a label, return false.  If it
   /// constant folds return true and set the folded value.
-  bool ConstantFoldsToSimpleInteger(const Expr *Cond, llvm::APSInt &Result);
-  
+  bool ConstantFoldsToSimpleInteger(const Expr *Cond, llvm::APSInt &Result,
+                                    bool AllowLabels = false);
+
   /// EmitBranchOnBoolExpr - Emit a branch on a boolean condition (e.g. for an
   /// if statement) to the specified blocks.  Based on the condition, this might
   /// try to simplify the codegen of the conditional based on the branch.