Do not add PHIs with no users when creating LCSSA form. Patch by Andrew Clinton.

llvm-svn: 127674

llvm/lib/Transforms/Utils/LCSSA.cpp

@@ -207,6 +207,8 @@ bool LCSSA::ProcessInstruction(Instruction *Inst,
 
   DomTreeNode *DomNode = DT->getNode(DomBB);
 
+  SmallVector<PHINode*, 16> AddedPHIs;
+
   SSAUpdater SSAUpdate;
   SSAUpdate.Initialize(Inst->getType(), Inst->getName());
   
@@ -236,6 +238,8 @@ bool LCSSA::ProcessInstruction(Instruction *Inst,
           &PN->getOperandUse(
             PN->getOperandNumForIncomingValue(PN->getNumIncomingValues()-1)));
     }
+
+    AddedPHIs.push_back(PN);
     
     // Remember that this phi makes the value alive in this block.
     SSAUpdate.AddAvailableValue(ExitBB, PN);
@@ -262,6 +266,12 @@ bool LCSSA::ProcessInstruction(Instruction *Inst,
     // Otherwise, do full PHI insertion.
     SSAUpdate.RewriteUse(*UsesToRewrite[i]);
   }
+
+  // Remove PHI nodes that did not have any uses rewritten.
+  for (unsigned i = 0, e = AddedPHIs.size(); i != e; ++i) {
+    if (!AddedPHIs[i]->hasNUsesOrMore(1))
+      AddedPHIs[i]->eraseFromParent();
+  }
   
   return true;
 }

llvm/test/Transforms/LCSSA/2006-06-03-IncorrectIDFPhis.ll

@@ -1,7 +1,5 @@
 ; RUN: opt < %s -loop-simplify -lcssa -S | \
 ; RUN:   grep {%%SJE.0.0.lcssa = phi .struct.SetJmpMapEntry}
-; RUN: opt < %s -loop-simplify -lcssa -S | \
-; RUN:   grep {%%SJE.0.0.lcssa1 = phi .struct.SetJmpMapEntry}
 
         %struct.SetJmpMapEntry = type { i8*, i32, %struct.SetJmpMapEntry* }
 

llvm/test/Transforms/LCSSA/unused-phis.ll

@@ -0,0 +1,38 @@
+; RUN: opt < %s -lcssa -S | FileCheck %s
+; CHECK: exit1:
+; CHECK: .lcssa =
+; CHECK: exit2:
+; CHECK: .lcssa2 =
+; CHECK: exit3:
+; CHECK-NOT: .lcssa1 =
+
+; Test to ensure that when there are multiple exit blocks, PHI nodes are
+; only inserted by LCSSA when there is a use dominated by a given exit
+; block.
+
+declare void @printf(i32 %i)
+
+define i32 @unused_phis() nounwind {
+entry:
+  br label %loop
+
+loop:
+  %i = phi i32 [0, %entry], [1, %then2]
+  br i1 undef, label %exit1, label %then1
+
+then1:
+  br i1 undef, label %exit2, label %then2
+
+then2:
+  br i1 undef, label %exit3, label %loop
+
+exit1:
+  call void @printf(i32 %i)
+  ret i32 %i
+
+exit2:
+  ret i32 %i
+
+exit3:
+  ret i32 0
+}