From 5b2749abf585f9e28656c289001c2327eed401af Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Wed, 7 Mar 2012 08:49:42 +0000
Subject: Where the BranchFolding pass removes a branch then adds another
 better branch, the DebugLoc information can be maintained throughout by
 grabbing the DebugLoc before the RemoveBranch and then passing the result to
 the InsertBranch. Patch by Andrew Stanford-Jason!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152212 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/BranchFolding.cpp | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

(limited to 'lib/CodeGen/BranchFolding.cpp')

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 59c92b3c68..f57f4a8e28 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -1019,12 +1019,27 @@ static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
   return MBB2I->isCall() && !MBB1I->isCall();
 }
 
+/// getBranchDebugLoc - Find and return, if any, the DebugLoc of the branch
+/// instructions on the block. Always use the DebugLoc of the first
+/// branching instruction found unless its absent, in which case use the
+/// DebugLoc of the second if present.
+static DebugLoc getBranchDebugLoc(MachineBasicBlock &MBB) {
+  MachineBasicBlock::iterator I = MBB.end();
+  if (I == MBB.begin())
+    return DebugLoc();
+  --I;
+  while (I->isDebugValue() && I != MBB.begin())
+    --I;
+  if (I->isBranch())
+    return I->getDebugLoc();
+  return DebugLoc();
+}
+
 /// OptimizeBlock - Analyze and optimize control flow related to the specified
 /// block.  This is never called on the entry block.
 bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
   bool MadeChange = false;
   MachineFunction &MF = *MBB->getParent();
-  DebugLoc dl;  // FIXME: this is nowhere
 ReoptimizeBlock:
 
   MachineFunction::iterator FallThrough = MBB;
@@ -1073,6 +1088,7 @@ ReoptimizeBlock:
     // destination, remove the branch, replacing it with an unconditional one or
     // a fall-through.
     if (PriorTBB && PriorTBB == PriorFBB) {
+      DebugLoc dl = getBranchDebugLoc(PrevBB);
       TII->RemoveBranch(PrevBB);
       PriorCond.clear();
       if (PriorTBB != MBB)
@@ -1130,6 +1146,7 @@ ReoptimizeBlock:
     // If the prior block branches somewhere else on the condition and here if
     // the condition is false, remove the uncond second branch.
     if (PriorFBB == MBB) {
+      DebugLoc dl = getBranchDebugLoc(PrevBB);
       TII->RemoveBranch(PrevBB);
       TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond, dl);
       MadeChange = true;
@@ -1143,6 +1160,7 @@ ReoptimizeBlock:
     if (PriorTBB == MBB) {
       SmallVector<MachineOperand, 4> NewPriorCond(PriorCond);
       if (!TII->ReverseBranchCondition(NewPriorCond)) {
+        DebugLoc dl = getBranchDebugLoc(PrevBB);
         TII->RemoveBranch(PrevBB);
         TII->InsertBranch(PrevBB, PriorFBB, 0, NewPriorCond, dl);
         MadeChange = true;
@@ -1180,6 +1198,7 @@ ReoptimizeBlock:
           DEBUG(dbgs() << "\nMoving MBB: " << *MBB
                        << "To make fallthrough to: " << *PriorTBB << "\n");
 
+          DebugLoc dl = getBranchDebugLoc(PrevBB);
           TII->RemoveBranch(PrevBB);
           TII->InsertBranch(PrevBB, MBB, 0, NewPriorCond, dl);
 
@@ -1209,6 +1228,7 @@ ReoptimizeBlock:
     if (CurTBB && CurFBB && CurFBB == MBB && CurTBB != MBB) {
       SmallVector<MachineOperand, 4> NewCond(CurCond);
       if (!TII->ReverseBranchCondition(NewCond)) {
+        DebugLoc dl = getBranchDebugLoc(*MBB);
         TII->RemoveBranch(*MBB);
         TII->InsertBranch(*MBB, CurFBB, CurTBB, NewCond, dl);
         MadeChange = true;
@@ -1222,6 +1242,7 @@ ReoptimizeBlock:
     if (CurTBB && CurCond.empty() && CurFBB == 0 &&
         IsBranchOnlyBlock(MBB) && CurTBB != MBB &&
         !MBB->hasAddressTaken()) {
+      DebugLoc dl = getBranchDebugLoc(*MBB);
       // This block may contain just an unconditional branch.  Because there can
       // be 'non-branch terminators' in the block, try removing the branch and
       // then seeing if the block is empty.
@@ -1264,8 +1285,9 @@ ReoptimizeBlock:
               assert(PriorFBB == 0 && "Machine CFG out of date!");
               PriorFBB = MBB;
             }
+            DebugLoc pdl = getBranchDebugLoc(PrevBB);
             TII->RemoveBranch(PrevBB);
-            TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, dl);
+            TII->InsertBranch(PrevBB, PriorTBB, PriorFBB, PriorCond, pdl);
           }
 
           // Iterate through all the predecessors, revectoring each in-turn.
@@ -1289,9 +1311,10 @@ ReoptimizeBlock:
               bool NewCurUnAnalyzable = TII->AnalyzeBranch(*PMBB, NewCurTBB,
                       NewCurFBB, NewCurCond, true);
               if (!NewCurUnAnalyzable && NewCurTBB && NewCurTBB == NewCurFBB) {
+                DebugLoc pdl = getBranchDebugLoc(*PMBB);
                 TII->RemoveBranch(*PMBB);
                 NewCurCond.clear();
-                TII->InsertBranch(*PMBB, NewCurTBB, 0, NewCurCond, dl);
+                TII->InsertBranch(*PMBB, NewCurTBB, 0, NewCurCond, pdl);
                 MadeChange = true;
                 ++NumBranchOpts;
                 PMBB->CorrectExtraCFGEdges(NewCurTBB, 0, false);
@@ -1351,7 +1374,7 @@ ReoptimizeBlock:
           if (CurFallsThru) {
             MachineBasicBlock *NextBB = llvm::next(MachineFunction::iterator(MBB));
             CurCond.clear();
-            TII->InsertBranch(*MBB, NextBB, 0, CurCond, dl);
+            TII->InsertBranch(*MBB, NextBB, 0, CurCond, DebugLoc());
           }
           MBB->moveAfter(PredBB);
           MadeChange = true;
-- 
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