llvm-reduce: Fix another invalid reduction with repeated input phis

[arsenm]

Summary

ReduceOperandsSkip had the same issue as ReduceOperands when handling
phis with repeated predecessors.

[arsenm]

7721cba2eeb41a45f002ee923cb7acef89fa7483

llvm/test/tools/llvm-reduce/reduce-operands-skip-repeated-phi-input.ll

+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=operands-skip --test FileCheck --test-arg --check-prefixes=CHECK-INTERESTINGNESS --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefixes=CHECK %s < %t
+
+; Make sure if we're replacing the value in a phi, it's replaced for
+; all repeats of the same incoming block.
+
+; CHECK-INTERESTINGNESS: switch
+; CHECK-INTERESTINGNESS: phi
+; CHECK-INTERESTINGNESS-SAME: [ %gep1, %bb1 ]
+
+; CHECK: %phi.ptr = phi ptr [ %arg1, %entry ], [ %arg1, %entry ], [ %gep1, %bb1 ]
+define void @foo(i32 %arg0, ptr %arg1, ptr %arg2) {
+entry:
+  %gep0 = getelementptr i32, ptr %arg1, i32 10
+  %gep1 = getelementptr i32, ptr %arg2, i32 12
+  switch i32 %arg0, label %ret [
+    i32 3, label %bb1
+    i32 4, label %bb2
+    i32 12, label %bb2
+  ]
+
+bb1:
+  br label %bb2
+
+bb2:
+  %phi.ptr = phi ptr [ %gep0, %entry ], [ %gep0, %entry ], [ %gep1, %bb1 ]
+  store volatile i32 0, ptr %phi.ptr
+  br label %ret
+
+ret:
+  ret void
+}

llvm/tools/llvm-reduce/deltas/ReduceOperandsSkip.cpp

opportunities(F, [&](Use &Op, ArrayRef<Value *> Candidates) {
         // set for the following operands. Delay it until after all candidates
         // have been determined.
         Replacements.push_back({&Op, C});
 
         AlreadyReplaced = true;
       }
     });
 
-    for (std::pair<Use *, Value *> P : Replacements)
+    for (std::pair<Use *, Value *> P : Replacements) {
+      if (PHINode *Phi = dyn_cast<PHINode>(P.first->getUser()))
+        Phi->setIncomingValueForBlock(Phi->getIncomingBlock(*P.first), P.second);
+      else
         P.first->set(P.second);
     }
   }
+}
 
 void llvm::reduceOperandsSkipDeltaPass(TestRunner &Test) {
   errs() << "*** Reducing operands by skipping over instructions ...\n";
   runDeltaPass(Test, extractOperandsFromModule);
 }