[flang] Implement lowering for the PAUSE statement (Fixes #166821) #167115

sathvikreddy853 · 2025-11-08T09:54:13Z

Implements lowering for the Fortran PAUSE statement.

Handles PAUSE with no operand.
Handles PAUSE with integer argument.
Handles PAUSE with character literal argument.
Adds a new lowering test: flang/test/Lower/pause-statement.f90.

Unlike STOP, PAUSE does not unconditionally terminate control flow.
The lowering preserves labels and GOTOs, consistent with legacy Fortran behavior.

Fixes: #166821

This patch adds lowering support for the Fortran PAUSE statement to FIR. It mirrors the STOP statement lowering logic to handle: - PAUSE with no operand - PAUSE <integer> - PAUSE 'message' Fixes llvm#166821.

github-actions · 2025-11-08T09:54:29Z

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llvmbot · 2025-11-08T09:54:58Z

@llvm/pr-subscribers-flang-fir-hlfir

Author: None (sathvikreddy853)

Changes

Implements lowering for the Fortran PAUSE statement.

Handles PAUSE with no operand.
Handles PAUSE with integer argument.
Handles PAUSE with character literal argument.
Adds a new lowering test: flang/test/Lower/pause-statement.f90.

Unlike STOP, PAUSE does not unconditionally terminate control flow.
The lowering preserves labels and GOTOs, consistent with legacy Fortran behavior.

Fixes: #166821

Full diff: https://github.com/llvm/llvm-project/pull/167115.diff

2 Files Affected:

(modified) flang/lib/Lower/Runtime.cpp (+48-4)
(modified) flang/test/Lower/pause-statement.f90 (+22-1)

diff --git a/flang/lib/Lower/Runtime.cpp b/flang/lib/Lower/Runtime.cpp
index cb555249125f6..48c70f4180de0 100644
--- a/flang/lib/Lower/Runtime.cpp
+++ b/flang/lib/Lower/Runtime.cpp
@@ -263,12 +263,56 @@ void Fortran::lower::genSyncTeamStatement(
 
 void Fortran::lower::genPauseStatement(
     Fortran::lower::AbstractConverter &converter,
-    const Fortran::parser::PauseStmt &) {
+    const Fortran::parser::PauseStmt &stmt) {
+  
   fir::FirOpBuilder &builder = converter.getFirOpBuilder();
   mlir::Location loc = converter.getCurrentLocation();
-  mlir::func::FuncOp callee =
-      fir::runtime::getRuntimeFunc<mkRTKey(PauseStatement)>(loc, builder);
-  fir::CallOp::create(builder, loc, callee, mlir::ValueRange{});
+  Fortran::lower::StatementContext stmtCtx;
+
+  llvm::SmallVector<mlir::Value> operands;
+  mlir::func::FuncOp callee;
+  mlir::FunctionType calleeType;
+
+  if (stmt.v.has_value()) {
+    const auto &code = stmt.v.value();
+    auto expr = converter.genExprValue(*Fortran::semantics::GetExpr(code), stmtCtx);
+    LLVM_DEBUG(llvm::dbgs() << "pause expression: "; expr.dump(); llvm::dbgs() << '\n');
+    expr.match(
+        // Character-valued expression -> call PauseStatementText (CHAR, LEN)
+        [&](const fir::CharBoxValue &x) {
+          callee = fir::runtime::getRuntimeFunc<mkRTKey(PauseStatementText)>(loc, builder);
+          calleeType = callee.getFunctionType();
+
+          operands.push_back(
+              builder.createConvert(loc, calleeType.getInput(0), x.getAddr()));
+          operands.push_back(
+              builder.createConvert(loc, calleeType.getInput(1), x.getLen()));
+        },
+        // Numeric/unboxed value -> call PauseStatement which accepts an integer code.
+        [&](fir::UnboxedValue x) {
+           callee = fir::runtime::getRuntimeFunc<mkRTKey(PauseStatement)>(loc, builder);
+           calleeType = callee.getFunctionType();
+            if (calleeType.getNumInputs() >= 1) {
+              mlir::Value cast =
+                builder.createConvert(loc, calleeType.getInput(0), x);
+            operands.push_back(cast);
+            }
+        },
+        [&](auto) {
+          mlir::emitError(loc, "unhandled expression in PAUSE");
+          std::exit(1);
+        });
+  } else {
+    callee = fir::runtime::getRuntimeFunc<mkRTKey(PauseStatement)>(loc, builder);
+    calleeType = callee.getFunctionType();
+  }
+  
+  fir::CallOp::create(builder, loc, callee, operands);
+
+  // NOTE: PAUSE should not unconditionally terminate the current block.
+  // Unlike STOP, PAUSE does not necessarily abandon control flow, so do not
+  // subsequent control flow (e.g. GOTO/branches) to be generated.
+  // insert genUnreachable() here. Leaving the block un-terminated allows
 }
 
 void Fortran::lower::genPointerAssociate(fir::FirOpBuilder &builder,
diff --git a/flang/test/Lower/pause-statement.f90 b/flang/test/Lower/pause-statement.f90
index f4c8f6fbc4385..926f81e96cefd 100644
--- a/flang/test/Lower/pause-statement.f90
+++ b/flang/test/Lower/pause-statement.f90
@@ -1,4 +1,4 @@
-! RUN: bbc %s -emit-fir --canonicalize -o - | FileCheck %s
+! RUN: bbc %s -emit-fir -hlfir=false --canonicalize -o - | FileCheck %s
 
 ! CHECK-LABEL: pause_test
 subroutine pause_test()
@@ -6,3 +6,24 @@ subroutine pause_test()
   ! CHECK-NEXT: return
   pause
 end subroutine
+
+! CHECK-LABEL: pause_code
+subroutine pause_code()
+  pause 42
+ ! CHECK: fir.call @_Fortran{{.*}}PauseStatement
+ ! CHECK-NEXT: return
+end subroutine
+
+! CHECK-LABEL: pause_msg
+subroutine pause_msg()
+  pause "hello"
+  ! CHECK-DAG: %[[five:.*]] = arith.constant 5 : index
+  ! CHECK-DAG: %[[lit:.*]] = fir.address_of(@_QQ{{.*}}) : !fir.ref<!fir.char<1,5>>
+  ! CHECK-DAG: %[[buff:.*]] = fir.convert %[[lit]] : (!fir.ref<!fir.char<1,5>>) -> !fir.ref<i8>
+  ! CHECK-DAG: %[[len:.*]] = fir.convert %[[five]] : (index) -> i64
+  ! CHECK: fir.call @_Fortran{{.*}}PauseStatementText(%[[buff]], %[[len]])
+  ! CHECK-NEXT: return
+end subroutine
+
+! CHECK-DAG: func private @_Fortran{{.*}}PauseStatement
+! CHECK-DAG: func private @_Fortran{{.*}}PauseStatementText
\ No newline at end of file

jeanPerier

Thanks for working on this.

flang/lib/Lower/Runtime.cpp

flang/test/Lower/pause-statement.f90

flang/lib/Lower/Runtime.cpp

sathvikreddy853 · 2025-11-21T07:43:42Z

Hey @jeanPerier, thanks for your review. I have made the required changes could you please review it once again.

jeanPerier

Thanks, few more nits, LGTM otherwise.

flang/lib/Lower/Runtime.cpp

flang/test/Lower/pause-statement.f90

eugeneepshteyn · 2025-11-21T16:14:39Z

Once Jean approves this PR, I want to run some internal tests before it's merged. ( @sathvikreddy853 won't be able to merge it anyway, so I'll take care of merging once I run the tests.)

…wering

sathvikreddy853 · 2025-11-22T08:05:20Z

Hey @jeanPerier and @eugeneepshteyn. I have made all the required changes. Could please take one more look at it?

sathvikreddy853 · 2025-11-25T05:45:19Z

Hi @jeanPerier, @eugeneepshteyn. Just a quick follow‑up (no rush at all). I’ve addressed the requested changes on this PAUSE lowering PR and would really appreciate another review when you have time.

jeanPerier

Please remove the --hlfir=false option on the test, LGTM otherwise, thanks.

flang/test/Lower/pause-statement.f90

Remove hlfir and add an additional check for hlfir.declare

sathvikreddy853 · 2025-11-25T17:32:34Z

Removed --hlfir=false and it seems to be running fine to me.

jeanPerier

LGTM, thanks

sathvikreddy853 · 2025-11-26T15:01:35Z

Thank you for the review and approval!

sathvikreddy853 · 2025-11-28T11:22:15Z

Hi @eugeneepshteyn, @jeanPerier has approved this PR. When you have a moment, could you please run the internal tests and handle the merge if everything looks good? Thanks!

eugeneepshteyn · 2025-11-30T00:47:02Z

I started the tests. Once it's all good, I'll merge this PR.

eugeneepshteyn

Both code and testing LGTM

github-actions · 2025-11-30T03:07:39Z

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sathvikreddy853 · 2025-11-30T15:31:21Z

Thanks a lot, @eugeneepshteyn and @jeanPerier. Sincerely appreciate your help on my first pull request.

llvm#167115) Implements lowering for the Fortran `PAUSE` statement. - Handles PAUSE with no operand. - Handles PAUSE with integer argument. - Handles PAUSE with character literal argument. - Adds a new lowering test: flang/test/Lower/pause-statement.f90. Unlike STOP, PAUSE does not unconditionally terminate control flow. The lowering preserves labels and GOTOs, consistent with legacy Fortran behavior. Fixes: llvm#166821 --------- Co-authored-by: aditya nath <[email protected]> Co-authored-by: Eugene Epshteyn <[email protected]>

sathvikreddy853 and others added 3 commits November 8, 2025 10:53

[flang] Lower PAUSE statement with code and message operands

faf6544

This patch adds lowering support for the Fortran PAUSE statement to FIR. It mirrors the STOP statement lowering logic to handle: - PAUSE with no operand - PAUSE <integer> - PAUSE 'message' Fixes llvm#166821.

[flang] add check for number of inputs and remove unreachable block code

8914d5e

[flang] Update pause-statement testcase

99974a0

Merge branch 'main' into flang/fix-pause-lowering

e616985

llvmbot added flang Flang issues not falling into any other category flang:fir-hlfir labels Nov 8, 2025

sathvikreddy853 added 2 commits November 8, 2025 15:32

Merge branch 'main' into flang/fix-pause-lowering

5faab4d

Merge branch 'main' into flang/fix-pause-lowering

fd9d218

eugeneepshteyn requested review from eugeneepshteyn and jeanPerier November 10, 2025 13:13

jeanPerier requested changes Nov 20, 2025

View reviewed changes

[flang] Address review feedback

0e8d546

sathvikreddy853 requested a review from jeanPerier November 21, 2025 07:42

jeanPerier reviewed Nov 21, 2025

View reviewed changes

flang/lib/Lower/Runtime.cpp Outdated Show resolved Hide resolved

flang/lib/Lower/Runtime.cpp Outdated Show resolved Hide resolved

flang/lib/Lower/Runtime.cpp Outdated Show resolved Hide resolved

flang/test/Lower/pause-statement.f90 Outdated Show resolved Hide resolved

[flang] Add missing argument to pause_code test and clean up PAUSE lo…

18b7e8f

…wering

sathvikreddy853 requested a review from jeanPerier November 22, 2025 08:05

Merge branch 'main' into flang/fix-pause-lowering

cd29c0e

jeanPerier reviewed Nov 25, 2025

View reviewed changes

flang/test/Lower/pause-statement.f90 Outdated Show resolved Hide resolved

[flang] Fix pause-statement testcase

b73c6c7

Remove hlfir and add an additional check for hlfir.declare

sathvikreddy853 requested a review from jeanPerier November 25, 2025 18:03

jeanPerier approved these changes Nov 26, 2025

View reviewed changes

Merge branch 'main' into flang/fix-pause-lowering

a0a69ca

eugeneepshteyn approved these changes Nov 30, 2025

View reviewed changes

Merge branch 'main' into flang/fix-pause-lowering

b096b28

eugeneepshteyn merged commit 70970d0 into llvm:main Nov 30, 2025
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[flang] Implement lowering for the PAUSE statement (Fixes #166821) #167115

[flang] Implement lowering for the PAUSE statement (Fixes #166821) #167115

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