SCEVExpander: Don't crash when trying to merge two constant phis.

Just constant fold them so they can't cause any trouble. Fixes PR12627.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166286 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ScalarEvolutionExpander.cpp

@@ -1618,6 +1618,17 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
          PEnd = Phis.end(); PIter != PEnd; ++PIter) {
     PHINode *Phi = *PIter;
 
+    // Fold constant phis. They may be congruent to other constant phis and
+    // would confuse the logic below that expects proper IVs.
+    if (Value *V = Phi->hasConstantValue()) {
+      Phi->replaceAllUsesWith(V);
+      DeadInsts.push_back(Phi);
+      ++NumElim;
+      DEBUG_WITH_TYPE(DebugType, dbgs()
+                      << "INDVARS: Eliminated constant iv: " << *Phi << '\n');
+      continue;
+    }
+
     if (!SE.isSCEVable(Phi->getType()))
       continue;
 

test/Transforms/IndVarSimplify/2012-10-19-congruent-constant.ll

@@ -0,0 +1,27 @@
+; RUN: opt -S -indvars < %s | FileCheck %s
+
+; PR12627
+define void @test1(i32 %x) nounwind uwtable ssp {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %phi1 = phi i1 [ false, %entry ], [ %cmpa, %for.body ]
+  %phi2 = phi i1 [ false, %entry ], [ %cmpb, %for.body ]
+  %i.07 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  tail call void @aux(i1 %phi1, i1 %phi2) nounwind
+  %cmpa = icmp sgt i32 %i.07, 200
+  %cmpb = icmp sgt i32 %i.07, 100
+  %inc = add nsw i32 %i.07, 1
+  %exitcond = icmp eq i32 %inc, 100
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+
+; CHECK: @test1
+; CHECK-NOT: phi i1
+; CHECK: call void @aux(i1 false, i1 false)
+}
+
+declare void @aux(i1, i1)

test/Transforms/IndVarSimplify/no-iv-rewrite.ll

@@ -199,7 +199,6 @@ entry:
 ; back to the loop iv.
 ;
 ; CHECK: loop:
-; CHECK: phi i32
 ; CHECK-NOT: phi
 ; CHECK: exit:
 loop: