From c07e19b2c1deab2e29747eec150cab9300bc38e2 Mon Sep 17 00:00:00 2001
From: Hal Finkel <hfinkel@anl.gov>
Date: Wed, 25 May 2016 21:53:24 +0000
Subject: Add a loop's debug location to its llvm.loop metadata

Getting accurate locations for loops is important, because those locations are
used by the frontend to generate optimization remarks. Currently, optimization
remarks for loops often appear on the wrong line, often the first line of the
loop body instead of the loop itself. This is confusing because that line might
itself be another loop, or might be somewhere else completely if the body was
an inlined function call. This happens because of the way we find the loop's
starting location. First, we look for a preheader, and if we find one, and its
terminator has a debug location, then we use that. Otherwise, we look for a
location on an instruction in the loop header.

The fallback heuristic is not bad, but will almost always find the beginning of
the body, and not the loop statement itself. The preheader location search
often fails because there's often not a preheader, and even when there is a
preheader, depending on how it was formed, it sometimes carries the location of
some preceeding code.

I don't see any good theoretical way to fix this problem. On the other hand,
this seems like a straightforward solution: Put the debug location in the
loop's llvm.loop metadata. When emitting debug information, this commit causes
us to add the debug location as an operand to each loop's llvm.loop metadata.
Thus, we now generate this metadata for all loops (not just loops with
optimization hints) when we're otherwise generating debug information.

The remark test case changes depend on the companion LLVM commit r270771.

llvm-svn: 270772
---
 clang/lib/CodeGen/CGLoopInfo.cpp | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

(limited to 'clang/lib/CodeGen/CGLoopInfo.cpp')

diff --git a/clang/lib/CodeGen/CGLoopInfo.cpp b/clang/lib/CodeGen/CGLoopInfo.cpp
index 08ed173f33e..e07fbb9bb3d 100644
--- a/clang/lib/CodeGen/CGLoopInfo.cpp
+++ b/clang/lib/CodeGen/CGLoopInfo.cpp
@@ -19,12 +19,14 @@
 using namespace clang::CodeGen;
 using namespace llvm;
 
-static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs) {
+static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs,
+                              llvm::DebugLoc Location) {
 
   if (!Attrs.IsParallel && Attrs.VectorizeWidth == 0 &&
       Attrs.InterleaveCount == 0 && Attrs.UnrollCount == 0 &&
       Attrs.VectorizeEnable == LoopAttributes::Unspecified &&
-      Attrs.UnrollEnable == LoopAttributes::Unspecified)
+      Attrs.UnrollEnable == LoopAttributes::Unspecified &&
+      !Location)
     return nullptr;
 
   SmallVector<Metadata *, 4> Args;
@@ -32,6 +34,10 @@ static MDNode *createMetadata(LLVMContext &Ctx, const LoopAttributes &Attrs) {
   auto TempNode = MDNode::getTemporary(Ctx, None);
   Args.push_back(TempNode.get());
 
+  // If we have a valid debug location for the loop, add it.
+  if (Location)
+    Args.push_back(Location.getAsMDNode());
+
   // Setting vectorize.width
   if (Attrs.VectorizeWidth > 0) {
     Metadata *Vals[] = {MDString::get(Ctx, "llvm.loop.vectorize.width"),
@@ -98,19 +104,21 @@ void LoopAttributes::clear() {
   UnrollEnable = LoopAttributes::Unspecified;
 }
 
-LoopInfo::LoopInfo(BasicBlock *Header, const LoopAttributes &Attrs)
+LoopInfo::LoopInfo(BasicBlock *Header, const LoopAttributes &Attrs,
+                   llvm::DebugLoc Location)
     : LoopID(nullptr), Header(Header), Attrs(Attrs) {
-  LoopID = createMetadata(Header->getContext(), Attrs);
+  LoopID = createMetadata(Header->getContext(), Attrs, Location);
 }
 
-void LoopInfoStack::push(BasicBlock *Header) {
-  Active.push_back(LoopInfo(Header, StagedAttrs));
+void LoopInfoStack::push(BasicBlock *Header, llvm::DebugLoc Location) {
+  Active.push_back(LoopInfo(Header, StagedAttrs, Location));
   // Clear the attributes so nested loops do not inherit them.
   StagedAttrs.clear();
 }
 
 void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
-                         ArrayRef<const clang::Attr *> Attrs) {
+                         ArrayRef<const clang::Attr *> Attrs,
+                         llvm::DebugLoc Location) {
 
   // Identify loop hint attributes from Attrs.
   for (const auto *Attr : Attrs) {
@@ -239,7 +247,7 @@ void LoopInfoStack::push(BasicBlock *Header, clang::ASTContext &Ctx,
   }
 
   /// Stage the attributes.
-  push(Header);
+  push(Header, Location);
 }
 
 void LoopInfoStack::pop() {
-- 
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