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

1 files changed, 10 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index 73a941a3682..a4f59fbc19d 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -629,7 +629,8 @@ void CodeGenFunction::EmitWhileStmt(const WhileStmt &S,
   JumpDest LoopHeader = getJumpDestInCurrentScope("while.cond");
   EmitBlock(LoopHeader.getBlock());
 
-  LoopStack.push(LoopHeader.getBlock(), CGM.getContext(), WhileAttrs);
+  LoopStack.push(LoopHeader.getBlock(), CGM.getContext(), WhileAttrs,
+                 Builder.getCurrentDebugLocation());
 
   // Create an exit block for when the condition fails, which will
   // also become the break target.
@@ -720,7 +721,8 @@ void CodeGenFunction::EmitDoStmt(const DoStmt &S,
   // Emit the body of the loop.
   llvm::BasicBlock *LoopBody = createBasicBlock("do.body");
 
-  LoopStack.push(LoopBody, CGM.getContext(), DoAttrs);
+  LoopStack.push(LoopBody, CGM.getContext(), DoAttrs,
+                 Builder.getCurrentDebugLocation());
 
   EmitBlockWithFallThrough(LoopBody, &S);
   {
@@ -772,6 +774,8 @@ void CodeGenFunction::EmitForStmt(const ForStmt &S,
 
   LexicalScope ForScope(*this, S.getSourceRange());
 
+  llvm::DebugLoc DL = Builder.getCurrentDebugLocation();
+
   // Evaluate the first part before the loop.
   if (S.getInit())
     EmitStmt(S.getInit());
@@ -783,7 +787,7 @@ void CodeGenFunction::EmitForStmt(const ForStmt &S,
   llvm::BasicBlock *CondBlock = Continue.getBlock();
   EmitBlock(CondBlock);
 
-  LoopStack.push(CondBlock, CGM.getContext(), ForAttrs);
+  LoopStack.push(CondBlock, CGM.getContext(), ForAttrs, DL);
 
   // If the for loop doesn't have an increment we can just use the
   // condition as the continue block.  Otherwise we'll need to create
@@ -868,6 +872,8 @@ CodeGenFunction::EmitCXXForRangeStmt(const CXXForRangeStmt &S,
 
   LexicalScope ForScope(*this, S.getSourceRange());
 
+  llvm::DebugLoc DL = Builder.getCurrentDebugLocation();
+
   // Evaluate the first pieces before the loop.
   EmitStmt(S.getRangeStmt());
   EmitStmt(S.getBeginStmt());
@@ -879,7 +885,7 @@ CodeGenFunction::EmitCXXForRangeStmt(const CXXForRangeStmt &S,
   llvm::BasicBlock *CondBlock = createBasicBlock("for.cond");
   EmitBlock(CondBlock);
 
-  LoopStack.push(CondBlock, CGM.getContext(), ForAttrs);
+  LoopStack.push(CondBlock, CGM.getContext(), ForAttrs, DL);
 
   // If there are any cleanups between here and the loop-exit scope,
   // create a block to stage a loop exit along.