[flang] Lower PAUSE statement

Lower the PAUSE statement to a runtime call.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: kiranchandramohan, schweitz

Differential Revision: https://reviews.llvm.org/D118699

Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>
Co-authored-by: Jean Perier <jperier@nvidia.com>

flang/lib/Lower/Bridge.cpp

@@ -547,7 +547,7 @@ private:
   }
 
   void genFIR(const Fortran::parser::PauseStmt &stmt) {
-    TODO(toLocation(), "PauseStmt lowering");
+    genPauseStatement(*this, stmt);
   }
 
   void genFIR(const Fortran::parser::FailImageStmt &stmt) {

flang/lib/Lower/Runtime.cpp

@@ -68,3 +68,13 @@ void Fortran::lower::genStopStatement(
   builder.create<fir::CallOp>(loc, callee, operands);
   genUnreachable(builder, loc);
 }
+
+void Fortran::lower::genPauseStatement(
+    Fortran::lower::AbstractConverter &converter,
+    const Fortran::parser::PauseStmt &) {
+  fir::FirOpBuilder &builder = converter.getFirOpBuilder();
+  mlir::Location loc = converter.getCurrentLocation();
+  mlir::FuncOp callee =
+      fir::runtime::getRuntimeFunc<mkRTKey(PauseStatement)>(loc, builder);
+  builder.create<fir::CallOp>(loc, callee, llvm::None);
+}

flang/test/Lower/pause-statement.f90

@@ -0,0 +1,8 @@
+! RUN: bbc %s -emit-fir --canonicalize -o - | FileCheck %s
+
+! CHECK-LABEL pause_test
+subroutine pause_test()
+  ! CHECK: fir.call @_Fortran{{.*}}PauseStatement()
+  ! CHECK-NEXT: return
+  pause
+end subroutine