[llvm] a43d257 - [ModuloSchedule] Fix terminator update when peeling.

[Hendrik Greving via llvm-commits]

Author: Hendrik Greving
Date: 2022-06-06T19:52:28Z
New Revision: a43d25734a46788da47a1a3786b3cd2bca540a72

URL: https://github.com/llvm/llvm-project/commit/a43d25734a46788da47a1a3786b3cd2bca540a72
DIFF: https://github.com/llvm/llvm-project/commit/a43d25734a46788da47a1a3786b3cd2bca540a72.diff

LOG: [ModuloSchedule] Fix terminator update when peeling.

Fixes a bug of us not correctly updating the terminator of the loop's
preheader, if multiple terminating branch instructions are present.

This is tested through existing tests. The bug itself is hard or not
possible to get exposed with the upstream Hexagon backend, because
the machine pipeliner checks for an existing preheader, which is
defined as a block with only 1 edge into the header.

The condition of this bug is a block into the loop with more than 1
edge, and not every downstream target checks for an existing preheader.

Differential Revision: https://reviews.llvm.org/D126386

Added: 
    

Modified: 
    llvm/lib/CodeGen/MachineLoopUtils.cpp
    llvm/lib/CodeGen/ModuloSchedule.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/MachineLoopUtils.cpp b/llvm/lib/CodeGen/MachineLoopUtils.cpp
index 94f25357a25c..6d0f90f8af1e 100644
--- a/llvm/lib/CodeGen/MachineLoopUtils.cpp
+++ b/llvm/lib/CodeGen/MachineLoopUtils.cpp
@@ -103,11 +103,10 @@ MachineBasicBlock *llvm::PeelSingleBlockLoop(LoopPeelDirection Direction,
 
   DebugLoc DL;
   if (Direction == LPD_Front) {
-    Preheader->replaceSuccessor(Loop, NewBB);
+    Preheader->ReplaceUsesOfBlockWith(Loop, NewBB);
     NewBB->addSuccessor(Loop);
     Loop->replacePhiUsesWith(Preheader, NewBB);
-    if (TII->removeBranch(*Preheader) > 0)
-      TII->insertBranch(*Preheader, NewBB, nullptr, {}, DL);
+    Preheader->updateTerminator(Loop);
     TII->removeBranch(*NewBB);
     TII->insertBranch(*NewBB, Loop, nullptr, {}, DL);
   } else {

diff  --git a/llvm/lib/CodeGen/ModuloSchedule.cpp b/llvm/lib/CodeGen/ModuloSchedule.cpp
index 20aecdf222e2..767c4840dc0f 100644
--- a/llvm/lib/CodeGen/ModuloSchedule.cpp
+++ b/llvm/lib/CodeGen/ModuloSchedule.cpp
@@ -1797,10 +1797,10 @@ void PeelingModuloScheduleExpander::peelPrologAndEpilogs() {
 
   // Iterate in reverse order over all instructions, remapping as we go.
   for (MachineBasicBlock *B : reverse(Blocks)) {
-    for (auto I = B->getFirstInstrTerminator()->getReverseIterator();
+    for (auto I = B->instr_rbegin();
          I != std::next(B->getFirstNonPHI()->getReverseIterator());) {
-      MachineInstr *MI = &*I++;
-      rewriteUsesOf(MI);
+      MachineBasicBlock::reverse_instr_iterator MI = I++;
+      rewriteUsesOf(&*MI);
     }
   }
   for (auto *MI : IllegalPhisToDelete) {