[DWARF] Allow duplication of tails with CFI instructions

This commit came as a result for revert of patch r317579 (originally
committed as r317100). The patch made CFI instructions duplicable, because
their existence in the epilogue block was affecting the Tail duplication
pass. However, duplicating blocks with CFI instructions was an issue for
compact unwind info on Darwin, which is why the patch was reverted.

This patch allows duplicating tails with CFI instructions, though they are
not duplicable, by copying them 'manually'.


Patch by Djordje Kovacevic.

Differential Revision: https://reviews.llvm.org/D40979

llvm-svn: 323883

1 files changed, 16 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TailDuplicator.cpp b/llvm/lib/CodeGen/TailDuplicator.cpp
index f51c884839b..b4ee8777d1f 100644
--- a/llvm/lib/CodeGen/TailDuplicator.cpp
+++ b/llvm/lib/CodeGen/TailDuplicator.cpp
@@ -37,6 +37,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetMachine.h"
 #include <algorithm>
 #include <cassert>
 #include <iterator>
@@ -371,6 +372,13 @@ void TailDuplicator::duplicateInstruction(
     MachineInstr *MI, MachineBasicBlock *TailBB, MachineBasicBlock *PredBB,
     DenseMap<unsigned, RegSubRegPair> &LocalVRMap,
     const DenseSet<unsigned> &UsedByPhi) {
+  // Allow duplication of CFI instructions.
+  if (MI->isCFIInstruction()) {
+    BuildMI(*PredBB, PredBB->end(), PredBB->findDebugLoc(PredBB->begin()),
+      TII->get(TargetOpcode::CFI_INSTRUCTION)).addCFIIndex(
+      MI->getOperand(0).getCFIIndex());
+    return;
+  }
   MachineInstr &NewMI = TII->duplicate(*PredBB, PredBB->end(), *MI);
   if (PreRegAlloc) {
     for (unsigned i = 0, e = NewMI.getNumOperands(); i != e; ++i) {
@@ -585,7 +593,13 @@ bool TailDuplicator::shouldTailDuplicate(bool IsSimple,
   unsigned InstrCount = 0;
   for (MachineInstr &MI : TailBB) {
     // Non-duplicable things shouldn't be tail-duplicated.
-    if (MI.isNotDuplicable())
+    // CFI instructions are marked as non-duplicable, because Darwin compact
+    // unwind info emission can't handle multiple prologue setups. In case of
+    // DWARF, allow them be duplicated, so that their existence doesn't prevent
+    // tail duplication of some basic blocks, that would be duplicated otherwise.
+    if (MI.isNotDuplicable() &&
+        (TailBB.getParent()->getTarget().getTargetTriple().isOSDarwin() ||
+        !MI.isCFIInstruction()))
       return false;
 
     // Convergent instructions can be duplicated only if doing so doesn't add
@@ -605,7 +619,7 @@ bool TailDuplicator::shouldTailDuplicate(bool IsSimple,
     if (PreRegAlloc && MI.isCall())
       return false;
 
-    if (!MI.isPHI() && !MI.isDebugValue())
+    if (!MI.isPHI() && !MI.isMetaInstruction())
       InstrCount += 1;
 
     if (InstrCount > MaxDuplicateCount)