[llvm] 94a2f9c - [GlobalISel] Fix CombinerHelper::isPredecessor for same def/use MI.

[Ahmed Bougacha via llvm-commits]

Author: Ahmed Bougacha
Date: 2021-09-15T16:45:27-07:00
New Revision: 94a2f9cdb6f9ef9843057030159ee69f76722121

URL: https://github.com/llvm/llvm-project/commit/94a2f9cdb6f9ef9843057030159ee69f76722121
DIFF: https://github.com/llvm/llvm-project/commit/94a2f9cdb6f9ef9843057030159ee69f76722121.diff

LOG: [GlobalISel] Fix CombinerHelper::isPredecessor for same def/use MI.

The doc comment for isPredecessor says:
  Returns true if \p DefMI precedes \p UseMI or they are the same
  instruction.
And dominates relies on that behavior for its own:
  Returns true if \p DefMI dominates \p UseMI. By definition an
  instruction dominates itself.

Make both statements correct by fixing isPredecessor.
Found by inspection.

Added: 
    

Modified: 
    llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index 701753b9c11ba..4cd4e2de73941 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -639,7 +639,7 @@ bool CombinerHelper::isPredecessor(const MachineInstr &DefMI,
          "shouldn't consider debug uses");
   assert(DefMI.getParent() == UseMI.getParent());
   if (&DefMI == &UseMI)
-    return false;
+    return true;
   const MachineBasicBlock &MBB = *DefMI.getParent();
   auto DefOrUse = find_if(MBB, [&DefMI, &UseMI](const MachineInstr &MI) {
     return &MI == &DefMI || &MI == &UseMI;