commit 7cd826a321d96af6581e0b1a5d6ec9ad26dcc6c1
author Sam Parker <sam.parker@arm.com> Mon Sep 04 08:12:16 2017 +0000
committer Sam Parker <sam.parker@arm.com> Mon Sep 04 08:12:16 2017 +0000
tree f23d88c5d107378b4c4b0127a9ea4011be21093a
parent 69e22789e1e8e65ec14b31586be76ce698933521

[LoopUnroll][DebugInfo] Don't add metadata to unrolled remainder loop

Debug information can be, and was, corrupted when the runtime
remainder loop was fully unrolled. This is because a !null node can
be created instead of a unique one describing the loop. In this case,
the original node gets incorrectly updated with the NewLoopID
metadata.

In the case when the remainder loop is going to be quickly fully
unrolled, there isn't the need to add loop metadata for it anyway.

Differential Revision: https://reviews.llvm.org/D37338

llvm-svn: 312471

llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp

diff --git a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
index cd5e977..01c9362 100644
--- a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -394,6 +394,12 @@
   if (CreateRemainderLoop) {
     Loop *NewLoop = NewLoops[L];
     assert(NewLoop && "L should have been cloned");
+
+    // Only add loop metadata if the loop is not going to be completely
+    // unrolled.
+    if (UnrollRemainder)
+      return NewLoop;
+
     // Add unroll disable metadata to disable future unrolling for this loop.
     SmallVector<Metadata *, 4> MDs;
     // Reserve first location for self reference to the LoopID metadata node.
@@ -414,13 +420,11 @@
     }
 
     LLVMContext &Context = NewLoop->getHeader()->getContext();
-    if (!UnrollRemainder) {
-      SmallVector<Metadata *, 1> DisableOperands;
-      DisableOperands.push_back(MDString::get(Context,
-                                              "llvm.loop.unroll.disable"));
-      MDNode *DisableNode = MDNode::get(Context, DisableOperands);
-      MDs.push_back(DisableNode);
-    }
+    SmallVector<Metadata *, 1> DisableOperands;
+    DisableOperands.push_back(MDString::get(Context,
+                                            "llvm.loop.unroll.disable"));
+    MDNode *DisableNode = MDNode::get(Context, DisableOperands);
+    MDs.push_back(DisableNode);
 
     MDNode *NewLoopID = MDNode::get(Context, MDs);
     // Set operand 0 to refer to the loop id itself.
@@ -536,6 +540,8 @@
                                       bool PreserveLCSSA) {
   DEBUG(dbgs() << "Trying runtime unrolling on Loop: \n");
   DEBUG(L->dump());
+  DEBUG(UseEpilogRemainder ? dbgs() << "Using epilog remainder.\n" :
+        dbgs() << "Using prolog remainder.\n");
 
   // Make sure the loop is in canonical form.
   if (!L->isLoopSimplifyForm()) {
@@ -892,6 +898,7 @@
   }
 
   if (remainderLoop && UnrollRemainder) {
+    DEBUG(dbgs() << "Unrolling remainder loop\n");
     UnrollLoop(remainderLoop, /*Count*/Count - 1, /*TripCount*/Count - 1,
                /*Force*/false, /*AllowRuntime*/false,
                /*AllowExpensiveTripCount*/false, /*PreserveCondBr*/true,