[PATCH] D70597: [PHIEliminate] skip dbg instruction when LowerPHINode

[Chris Ye via Phabricator via llvm-commits]

yechunliang updated this revision to Diff 246187.
yechunliang added a comment.

updated patch:
 [PHIEliminate] splice dbg instruction when LowerPHINode
DBG_VALUEs between PHI and LABEL will block PHI lownering after LABEL, move all DBG_VALUEs after Label before PHI lowering.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D70597/new/

https://reviews.llvm.org/D70597

Files:
  llvm/lib/CodeGen/PHIElimination.cpp
  llvm/test/CodeGen/X86/phi-node-elimination-dbg-invariant.mir


Index: llvm/test/CodeGen/X86/phi-node-elimination-dbg-invariant.mir
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/phi-node-elimination-dbg-invariant.mir
@@ -0,0 +1,30 @@
+# RUN: llc -mtriple=x86_64-- -run-pass phi-node-elimination -o - %s | FileCheck %s
+# Debug instruction should not impact PHI node lowering after LABEL, move DBG_VALUEs
+# after LABEL before PHI lowering.
+# Fix issue: https://bugs.llvm.org/show_bug.cgi?id=43859
+
+---
+name:            test1
+tracksRegLiveness: true
+body:             |
+  ; Verify PHI lowering with a debug instruction between PHI and LABEL,
+  ; skip debug instruction and insert copy instruction after LABEL.
+  ; CHECK-LABEL: name: test1
+  ; CHECK: bb.2:
+  ; CHECK: EH_LABEL 0
+  ; CHECK-NEXT: %1:gr32 = COPY %3
+  ; CHECK-NEXT: DBG_VALUE %1
+  ; CHECK-NEXT: DBG_VALUE %2
+  bb.0:
+    %0:gr32 = IMPLICIT_DEF
+    JMP_1 %bb.2
+
+  bb.1:
+
+  bb.2:
+    %1:gr32 = PHI %0, %bb.0, %2, %bb.1
+    DBG_VALUE %1
+    EH_LABEL 0
+    DBG_VALUE %2
+    %2:gr32 = ADD32ri8 killed %1, 1, implicit-def $eflags
+...
Index: llvm/lib/CodeGen/PHIElimination.cpp
===================================================================
--- llvm/lib/CodeGen/PHIElimination.cpp
+++ llvm/lib/CodeGen/PHIElimination.cpp
@@ -199,6 +199,21 @@
   return Changed;
 }
 
+void spliceDebugInstructionForward(MachineBasicBlock &MBB,
+                                   MachineBasicBlock::iterator From,
+                                   MachineBasicBlock::iterator To) {
+  if (From == To)
+    return;
+
+  for (MachineBasicBlock::iterator Inst = std::prev(To); Inst != From; --Inst) {
+    MachineBasicBlock::iterator where = std::next(To);
+    if(Inst->isDebugInstr()) {
+      MBB.splice(where, &MBB, Inst);
+      Inst = std::prev(Inst);
+    }
+  }
+}
+
 /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in
 /// predecessor basic blocks.
 bool PHIElimination::EliminatePHINodes(MachineFunction &MF,
@@ -207,8 +222,11 @@
     return false;   // Quick exit for basic blocks without PHIs.
 
   // Get an iterator to the last PHI node.
-  MachineBasicBlock::iterator LastPHIIt =
-    std::prev(MBB.SkipPHIsAndLabels(MBB.begin()));
+  MachineBasicBlock::iterator LastPHIIt = skipDebugInstructionsBackward(
+    std::prev(MBB.SkipPHIsLabelsAndDebug(MBB.begin())), MBB.begin());
+
+  if (LastPHIIt->isLabel())
+    spliceDebugInstructionForward(MBB, MBB.begin(), LastPHIIt);
 
   while (MBB.front().isPHI())
     LowerPHINode(MBB, LastPHIIt);


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