[PATCH] D80116: [IR] Simplify Use::swap. NFCI.

[Jay Foad via Phabricator via llvm-commits]

foad created this revision.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

The new implementation makes it clear that there are exactly two
conditional stores (after the initial no-op optimization). By contrast
the old implementation had seven conditionals, some hidden inside other
functions.

This commit can change the order of operands in operand lists, hence the
tweak to one test case.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D80116

Files:
  llvm/lib/IR/Use.cpp
  llvm/test/Transforms/LoopReroll/nonconst_lb.ll


Index: llvm/test/Transforms/LoopReroll/nonconst_lb.ll
===================================================================
--- llvm/test/Transforms/LoopReroll/nonconst_lb.ll
+++ llvm/test/Transforms/LoopReroll/nonconst_lb.ll
@@ -48,7 +48,7 @@
   ret void
 }
 ; CHECK-LABEL: @foo
-; CHECK: for.body.preheader:                               ; preds = %entry
+; CHECK: for.body.preheader:
 ; CHECK:   %0 = add i32 %n, -1
 ; CHECK:   %1 = sub i32 %0, %m
 ; CHECK:   %2 = lshr i32 %1, 2
@@ -56,7 +56,7 @@
 ; CHECK:   %4 = add i32 %3, 3
 ; CHECK:   br label %for.body
 
-; CHECK: for.body:                                         ; preds = %for.body, %for.body.preheader
+; CHECK: for.body:
 ; CHECK:   %indvar = phi i32 [ 0, %for.body.preheader ], [ %indvar.next, %for.body ]
 ; CHECK:   %5 = add i32 %m, %indvar
 ; CHECK:   %arrayidx = getelementptr inbounds i32, i32* %B, i32 %5
Index: llvm/lib/IR/Use.cpp
===================================================================
--- llvm/lib/IR/Use.cpp
+++ llvm/lib/IR/Use.cpp
@@ -17,24 +17,17 @@
   if (Val == RHS.Val)
     return;
 
-  if (Val)
-    removeFromList();
-
-  Value *OldVal = Val;
-  if (RHS.Val) {
-    RHS.removeFromList();
-    Val = RHS.Val;
-    Val->addUse(*this);
-  } else {
-    Val = nullptr;
-  }
-
-  if (OldVal) {
-    RHS.Val = OldVal;
-    RHS.Val->addUse(RHS);
-  } else {
-    RHS.Val = nullptr;
-  }
+  std::swap(Val, RHS.Val);
+  std::swap(Next, RHS.Next);
+  std::swap(Prev, RHS.Prev);
+
+  *Prev = this;
+  if (Next)
+    Next->Prev = &Next;
+
+  *RHS.Prev = &RHS;
+  if (RHS.Next)
+    RHS.Next->Prev = &RHS.Next;
 }
 
 unsigned Use::getOperandNo() const {


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