From 7a49d50f22ad577d91cda7904c8a162c2cecd4a8 Mon Sep 17 00:00:00 2001
From: Tom Eccles <tom.eccles@arm.com>
Date: Mon, 13 Feb 2023 15:45:47 +0000
Subject: [PATCH] [flang] support fir.unreachable in stack arrays pass

Some functions (e.g. the main function) end with a call to the STOP
statement instead of a func.return. This is lowered as a call to the
stop runtime function followed by a fir.unreachable. fir.unreachable is
a terminator and so this can cause functions to have no func.return.

The stack arrays pass looks to see which heap allocations have always
been freed by the time a function returns. Without any returns, the pass
does not detect any freed allocations. This patch changes this behaviour
so that fir.unreachable is checked as well as func.return.

This allows 15 heap allocations for array temporaries in spec2017
exchange2's main function to be moved to the stack.

Differential Revision: https://reviews.llvm.org/D143918
---
 flang/lib/Optimizer/Transforms/StackArrays.cpp |  8 +++++---
 flang/test/Transforms/stack-arrays.fir         | 17 +++++++++++++++++
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/flang/lib/Optimizer/Transforms/StackArrays.cpp b/flang/lib/Optimizer/Transforms/StackArrays.cpp
index a0cd6de..c0a981e 100644
--- a/flang/lib/Optimizer/Transforms/StackArrays.cpp
+++ b/flang/lib/Optimizer/Transforms/StackArrays.cpp
@@ -431,12 +431,14 @@ void StackArraysAnalysisWrapper::analyseFunction(mlir::Operation *func) {
   }
 
   LatticePoint point{func};
-  func->walk([&](mlir::func::ReturnOp child) {
-    const LatticePoint *lattice = solver.lookupState<LatticePoint>(child);
+  auto joinOperationLattice = [&](mlir::Operation *op) {
+    const LatticePoint *lattice = solver.lookupState<LatticePoint>(op);
     // there will be no lattice for an unreachable block
     if (lattice)
       point.join(*lattice);
-  });
+  };
+  func->walk([&](mlir::func::ReturnOp child) { joinOperationLattice(child); });
+  func->walk([&](fir::UnreachableOp child) { joinOperationLattice(child); });
   llvm::DenseSet<mlir::Value> freedValues;
   point.appendFreedValues(freedValues);
 
diff --git a/flang/test/Transforms/stack-arrays.fir b/flang/test/Transforms/stack-arrays.fir
index d34d662..7b73bf0 100644
--- a/flang/test/Transforms/stack-arrays.fir
+++ b/flang/test/Transforms/stack-arrays.fir
@@ -307,3 +307,20 @@ func.func @omp_placement1() {
 // CHECK-NEXT:   }
 // CHECK-NEXT:   return
 // CHECK-NEXT: }
+
+// function terminated by stop statement
+func.func @stop_terminator() {
+  %0 = fir.allocmem !fir.array<42xi32>
+  fir.freemem %0 : !fir.heap<!fir.array<42xi32>>
+  %c0_i32 = arith.constant 0 : i32
+  %false = arith.constant false
+  %none = fir.call @_FortranAStopStatement(%c0_i32, %false, %false) : (i32, i1, i1) -> none
+  fir.unreachable
+}
+// CHECK: func.func @stop_terminator() {
+// CHECK-NEXT: fir.alloca !fir.array<42xi32>
+// CHECK-NEXT:  %[[ZERO:.*]] = arith.constant 0 : i32
+// CHECK-NEXT:  %[[FALSE:.*]] = arith.constant false
+// CHECK-NEXT:  %[[NONE:.*]] = fir.call @_FortranAStopStatement(%[[ZERO]], %[[FALSE]], %[[FALSE]]) : (i32, i1, i1) -> none
+// CHECK-NEXT:  fir.unreachable
+// CHECK-NEXT: }
-- 
2.7.4