[PATCH] D15561: [OpenMP] Remove explicit call for implicit barrier

[Jonas Hahnfeld via cfe-commits]

Hahnfeld created this revision.
Hahnfeld added reviewers: ABataev, hfinkel, kkwli0, rjmccall.
Hahnfeld added a subscriber: cfe-commits.

`#pragma omp parallel` needs an implicit barrier that is currently done by an 
explicit call to `__kmpc_barrier`. However, the runtime already ensures a 
barrier in `__kmpc_fork_call` which currently leads to two barriers per region 
per thread.

Or are there any corner cases where this is needed? I couldn't make up a test 
case...

http://reviews.llvm.org/D15561

Files:
  lib/CodeGen/CGStmtOpenMP.cpp

Index: lib/CodeGen/CGStmtOpenMP.cpp
===================================================================
--- lib/CodeGen/CGStmtOpenMP.cpp
+++ lib/CodeGen/CGStmtOpenMP.cpp
@@ -879,10 +879,7 @@
     (void)PrivateScope.Privatize();
     CGF.EmitStmt(cast<CapturedStmt>(S.getAssociatedStmt())->getCapturedStmt());
     CGF.EmitOMPReductionClauseFinal(S);
-    // Emit implicit barrier at the end of the 'parallel' directive.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_unknown, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_parallel, CodeGen);
 }
@@ -1847,12 +1844,7 @@
   (void)emitScheduleClause(*this, S, /*OuterRegion=*/true);
   auto &&CodeGen = [&S](CodeGenFunction &CGF) {
     CGF.EmitOMPWorksharingLoop(S);
-    // Emit implicit barrier at the end of parallel region, but this barrier
-    // is at the end of 'for' directive, so emit it as the implicit barrier for
-    // this 'for' directive.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_parallel, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_for, CodeGen);
 }
@@ -1865,12 +1857,7 @@
   (void)emitScheduleClause(*this, S, /*OuterRegion=*/true);
   auto &&CodeGen = [&S](CodeGenFunction &CGF) {
     CGF.EmitOMPWorksharingLoop(S);
-    // Emit implicit barrier at the end of parallel region, but this barrier
-    // is at the end of 'for' directive, so emit it as the implicit barrier for
-    // this 'for' directive.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_parallel, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_simd, CodeGen);
 }
@@ -1882,10 +1869,7 @@
   LexicalScope Scope(*this, S.getSourceRange());
   auto &&CodeGen = [&S](CodeGenFunction &CGF) {
     (void)CGF.EmitSections(S);
-    // Emit implicit barrier at the end of parallel region.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_parallel, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_sections, CodeGen);
 }



Index: lib/CodeGen/CGStmtOpenMP.cpp
===================================================================
--- lib/CodeGen/CGStmtOpenMP.cpp
+++ lib/CodeGen/CGStmtOpenMP.cpp
@@ -879,10 +879,7 @@
     (void)PrivateScope.Privatize();
     CGF.EmitStmt(cast<CapturedStmt>(S.getAssociatedStmt())->getCapturedStmt());
     CGF.EmitOMPReductionClauseFinal(S);
-    // Emit implicit barrier at the end of the 'parallel' directive.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_unknown, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_parallel, CodeGen);
 }
@@ -1847,12 +1844,7 @@
   (void)emitScheduleClause(*this, S, /*OuterRegion=*/true);
   auto &&CodeGen = [&S](CodeGenFunction &CGF) {
     CGF.EmitOMPWorksharingLoop(S);
-    // Emit implicit barrier at the end of parallel region, but this barrier
-    // is at the end of 'for' directive, so emit it as the implicit barrier for
-    // this 'for' directive.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_parallel, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_for, CodeGen);
 }
@@ -1865,12 +1857,7 @@
   (void)emitScheduleClause(*this, S, /*OuterRegion=*/true);
   auto &&CodeGen = [&S](CodeGenFunction &CGF) {
     CGF.EmitOMPWorksharingLoop(S);
-    // Emit implicit barrier at the end of parallel region, but this barrier
-    // is at the end of 'for' directive, so emit it as the implicit barrier for
-    // this 'for' directive.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_parallel, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_simd, CodeGen);
 }
@@ -1882,10 +1869,7 @@
   LexicalScope Scope(*this, S.getSourceRange());
   auto &&CodeGen = [&S](CodeGenFunction &CGF) {
     (void)CGF.EmitSections(S);
-    // Emit implicit barrier at the end of parallel region.
-    CGF.CGM.getOpenMPRuntime().emitBarrierCall(
-        CGF, S.getLocStart(), OMPD_parallel, /*EmitChecks=*/false,
-        /*ForceSimpleCall=*/true);
+    // Implicit barrier is done by runtime in __kmpc_fork_call.
   };
   emitCommonOMPParallelDirective(*this, S, OMPD_sections, CodeGen);
 }

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