The patch set unroll disable pragma when unroll

with user specified count has been applied.

Summary:
Previously SetLoopAlreadyUnrolled() set the disable pragma only if
there was some loop metadata.
Now it set the pragma in all cases. This helps to prevent multiple
unroll when -unroll-count=N is given.

Reviewers: mzolotukhin

Differential Revision: http://reviews.llvm.org/D20765

From: Evgeny Stupachenko <evstupac@gmail.com>
llvm-svn: 272195

2 files changed, 36 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index ddc1c60d93e..65eab475b69 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -604,22 +604,22 @@ static unsigned UnrollCountPragmaValue(const Loop *L) {
 // unrolling pass is run more than once (which it generally is).
 static void SetLoopAlreadyUnrolled(Loop *L) {
   MDNode *LoopID = L->getLoopID();
-  if (!LoopID)
-    return;
-
   // First remove any existing loop unrolling metadata.
   SmallVector<Metadata *, 4> MDs;
   // Reserve first location for self reference to the LoopID metadata node.
   MDs.push_back(nullptr);
-  for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
-    bool IsUnrollMetadata = false;
-    MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
-    if (MD) {
-      const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
-      IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
+
+  if (LoopID) {
+    for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
+      bool IsUnrollMetadata = false;
+      MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
+      if (MD) {
+        const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
+        IsUnrollMetadata = S && S->getString().startswith("llvm.loop.unroll.");
+      }
+      if (!IsUnrollMetadata)
+        MDs.push_back(LoopID->getOperand(i));
     }
-    if (!IsUnrollMetadata)
-      MDs.push_back(LoopID->getOperand(i));
   }
 
   // Add unroll(disable) metadata to disable future unrolling.
diff --git a/llvm/test/Transforms/LoopUnroll/unroll-count.ll b/llvm/test/Transforms/LoopUnroll/unroll-count.ll
new file mode 100644
index 00000000000..f22c22bab0f
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnroll/unroll-count.ll
@@ -0,0 +1,25 @@
+; RUN: opt < %s -S -loop-unroll -unroll-count=2 | FileCheck %s
+; Checks that "llvm.loop.unroll.disable" is set when
+; unroll with count set by user has been applied.
+;
+; CHECK-LABEL: @foo(
+; CHECK: llvm.loop.unroll.disable
+
+define void @foo(i32* nocapture %a) {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  %inc = add nsw i32 %0, 1
+  store i32 %inc, i32* %arrayidx, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp eq i64 %indvars.iv.next, 64
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+