Patch to fix pragma metadata for do-while loops

Summary:
Make sure that loop metadata only is put on the backedge
when expanding a do-while loop.
Previously we added the loop metadata also on the branch
in the pre-header. That could confuse optimization passes
and result in the loop metadata being associated with the
wrong loop.

Fixes https://bugs.llvm.org/show_bug.cgi?id=38011

Committing on behalf of deepak2427 (Deepak Panickal)

Reviewers: #clang, ABataev, hfinkel, aaron.ballman, bjope

Reviewed By: bjope

Subscribers: bjope, rsmith, shenhan, zzheng, xbolva00, lebedev.ri, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D48721

llvm-svn: 336717

clang/lib/CodeGen/CGStmt.cpp

@@ -777,11 +777,6 @@ void CodeGenFunction::EmitDoStmt(const DoStmt &S,
   // Emit the body of the loop.
   llvm::BasicBlock *LoopBody = createBasicBlock("do.body");
 
-  const SourceRange &R = S.getSourceRange();
-  LoopStack.push(LoopBody, CGM.getContext(), DoAttrs,
-                 SourceLocToDebugLoc(R.getBegin()),
-                 SourceLocToDebugLoc(R.getEnd()));
-
   EmitBlockWithFallThrough(LoopBody, &S);
   {
     RunCleanupsScope BodyScope(*this);
@@ -790,6 +785,11 @@ void CodeGenFunction::EmitDoStmt(const DoStmt &S,
 
   EmitBlock(LoopCond.getBlock());
 
+  const SourceRange &R = S.getSourceRange();
+  LoopStack.push(LoopBody, CGM.getContext(), DoAttrs,
+                 SourceLocToDebugLoc(R.getBegin()),
+                 SourceLocToDebugLoc(R.getEnd()));
+
   // C99 6.8.5.2: "The evaluation of the controlling expression takes place
   // after each execution of the loop body."
 

clang/test/CodeGen/pragma-do-while.cpp

@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+
+// We expect to get a loop structure like this:
+//    do.body:                                       ; preds = %do.cond, ...
+//      ...
+//      br label %do.cond
+//    do.cond:                                       ; preds = %do.body
+//      ...
+//      br i1 %cmp, label %do.body, label %do.end
+//    do.end:                                        ; preds = %do.cond
+//      ...
+//
+// Verify that the loop metadata only is put on the backedge.
+//
+// CHECK-NOT: llvm.loop
+// CHECK-LABEL: do.cond:
+// CHECK: br {{.*}}, label %do.body, label %do.end, !llvm.loop ![[LMD1:[0-9]+]]
+// CHECK-LABEL: do.end:
+// CHECK-NOT: llvm.loop
+// CHECK: ![[LMD1]] = distinct !{![[LMD1]], ![[LMD2:[0-9]+]]}
+// CHECK: ![[LMD2]] = !{!"llvm.loop.unroll.count", i32 4}
+
+int test(int a[], int n) {
+  int i = 0;
+  int sum = 0;
+
+#pragma unroll 4
+  do
+  {
+    a[i] = a[i] + 1;
+    sum = sum + a[i];
+    i++;
+  } while (i < n);
+
+  return sum;
+}