[SCEVExpander] Fix a failed cast<> assertion

SCEVExpander::replaceCongruentIVs assumes the backedge value of an
SCEV-analysable PHI to always be an instruction, when this is not
necessarily true.  For now address this by bailing out of the
optimization if the backedge value of the PHI is a non-Instruction.

llvm-svn: 269213

2 files changed, 117 insertions, 43 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index c71f1a51382..0f07d3f57e2 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1794,51 +1794,55 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
       continue;
 
     if (BasicBlock *LatchBlock = L->getLoopLatch()) {
-      Instruction *OrigInc =
-        cast<Instruction>(OrigPhiRef->getIncomingValueForBlock(LatchBlock));
+      Instruction *OrigInc = dyn_cast<Instruction>(
+          OrigPhiRef->getIncomingValueForBlock(LatchBlock));
       Instruction *IsomorphicInc =
-        cast<Instruction>(Phi->getIncomingValueForBlock(LatchBlock));
-
-      // If this phi has the same width but is more canonical, replace the
-      // original with it. As part of the "more canonical" determination,
-      // respect a prior decision to use an IV chain.
-      if (OrigPhiRef->getType() == Phi->getType() &&
-          !(ChainedPhis.count(Phi) ||
-            isExpandedAddRecExprPHI(OrigPhiRef, OrigInc, L)) &&
-          (ChainedPhis.count(Phi) ||
-           isExpandedAddRecExprPHI(Phi, IsomorphicInc, L))) {
-        std::swap(OrigPhiRef, Phi);
-        std::swap(OrigInc, IsomorphicInc);
-      }
-      // Replacing the congruent phi is sufficient because acyclic redundancy
-      // elimination, CSE/GVN, should handle the rest. However, once SCEV proves
-      // that a phi is congruent, it's often the head of an IV user cycle that
-      // is isomorphic with the original phi. It's worth eagerly cleaning up the
-      // common case of a single IV increment so that DeleteDeadPHIs can remove
-      // cycles that had postinc uses.
-      const SCEV *TruncExpr = SE.getTruncateOrNoop(SE.getSCEV(OrigInc),
-                                                   IsomorphicInc->getType());
-      if (OrigInc != IsomorphicInc && TruncExpr == SE.getSCEV(IsomorphicInc) &&
-          SE.LI.replacementPreservesLCSSAForm(IsomorphicInc, OrigInc) &&
-          hoistIVInc(OrigInc, IsomorphicInc)) {
-        DEBUG_WITH_TYPE(DebugType,
-                        dbgs() << "INDVARS: Eliminated congruent iv.inc: "
-                               << *IsomorphicInc << '\n');
-        Value *NewInc = OrigInc;
-        if (OrigInc->getType() != IsomorphicInc->getType()) {
-          Instruction *IP = nullptr;
-          if (PHINode *PN = dyn_cast<PHINode>(OrigInc))
-            IP = &*PN->getParent()->getFirstInsertionPt();
-          else
-            IP = OrigInc->getNextNode();
-
-          IRBuilder<> Builder(IP);
-          Builder.SetCurrentDebugLocation(IsomorphicInc->getDebugLoc());
-          NewInc = Builder.
-            CreateTruncOrBitCast(OrigInc, IsomorphicInc->getType(), IVName);
+          dyn_cast<Instruction>(Phi->getIncomingValueForBlock(LatchBlock));
+
+      if (OrigInc && IsomorphicInc) {
+        // If this phi has the same width but is more canonical, replace the
+        // original with it. As part of the "more canonical" determination,
+        // respect a prior decision to use an IV chain.
+        if (OrigPhiRef->getType() == Phi->getType() &&
+            !(ChainedPhis.count(Phi) ||
+              isExpandedAddRecExprPHI(OrigPhiRef, OrigInc, L)) &&
+            (ChainedPhis.count(Phi) ||
+             isExpandedAddRecExprPHI(Phi, IsomorphicInc, L))) {
+          std::swap(OrigPhiRef, Phi);
+          std::swap(OrigInc, IsomorphicInc);
+        }
+        // Replacing the congruent phi is sufficient because acyclic
+        // redundancy elimination, CSE/GVN, should handle the
+        // rest. However, once SCEV proves that a phi is congruent,
+        // it's often the head of an IV user cycle that is isomorphic
+        // with the original phi. It's worth eagerly cleaning up the
+        // common case of a single IV increment so that DeleteDeadPHIs
+        // can remove cycles that had postinc uses.
+        const SCEV *TruncExpr =
+            SE.getTruncateOrNoop(SE.getSCEV(OrigInc), IsomorphicInc->getType());
+        if (OrigInc != IsomorphicInc &&
+            TruncExpr == SE.getSCEV(IsomorphicInc) &&
+            SE.LI.replacementPreservesLCSSAForm(IsomorphicInc, OrigInc) &&
+            hoistIVInc(OrigInc, IsomorphicInc)) {
+          DEBUG_WITH_TYPE(DebugType,
+                          dbgs() << "INDVARS: Eliminated congruent iv.inc: "
+                                 << *IsomorphicInc << '\n');
+          Value *NewInc = OrigInc;
+          if (OrigInc->getType() != IsomorphicInc->getType()) {
+            Instruction *IP = nullptr;
+            if (PHINode *PN = dyn_cast<PHINode>(OrigInc))
+              IP = &*PN->getParent()->getFirstInsertionPt();
+            else
+              IP = OrigInc->getNextNode();
+
+            IRBuilder<> Builder(IP);
+            Builder.SetCurrentDebugLocation(IsomorphicInc->getDebugLoc());
+            NewInc = Builder.CreateTruncOrBitCast(
+                OrigInc, IsomorphicInc->getType(), IVName);
+          }
+          IsomorphicInc->replaceAllUsesWith(NewInc);
+          DeadInsts.emplace_back(IsomorphicInc);
         }
-        IsomorphicInc->replaceAllUsesWith(NewInc);
-        DeadInsts.emplace_back(IsomorphicInc);
       }
     }
     DEBUG_WITH_TYPE(DebugType, dbgs() << "INDVARS: Eliminated congruent iv: "
diff --git a/llvm/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll b/llvm/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll
index 887b9db7f25..0adb92d671b 100644
--- a/llvm/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll
+++ b/llvm/test/Analysis/ScalarEvolution/expander-replace-congruent-ivs.ll
@@ -39,3 +39,73 @@ loop_1:
 leave:
   ret void
 }
+
+
+; @ReplaceArg_0 and @ReplaceArg_1 used to trigger a failed cast<>
+; assertion in SCEVExpander.
+
+define void @ReplaceArg_0(i32 %val) {
+; CHECK-LABEL: @ReplaceArg_0(
+entry:
+  br i1 undef, label %loop_0.cond, label %for.body.us
+
+for.body.us:
+  br label %loop_0.cond
+
+loop_0.cond:
+  br i1 true, label %loop_0.ph, label %loop_1.ph
+
+loop_0.ph:
+  br label %loop_0
+
+loop_1.exit:
+  br label %loop_1.ph
+
+loop_1.ph:
+  %c.lcssa = phi i32 [ 0, %loop_0.cond ], [ %val, %loop_1.exit ]
+  br label %loop_1
+
+loop_0:
+  br i1 undef, label %loop_0, label %loop_1.exit
+
+loop_1:
+  %d.1 = phi i32 [ %c.lcssa, %loop_1 ], [ %val, %loop_1.ph ]
+  %t.1 = phi i32 [ %val, %loop_1 ], [ %c.lcssa, %loop_1.ph ]
+  br i1 undef, label %leave, label %loop_1
+
+leave:
+  ret void
+}
+
+define void @ReplaceArg_1(i32 %val) {
+; CHECK-LABEL: @ReplaceArg_1(
+entry:
+  br i1 undef, label %loop_0.cond, label %for.body.us
+
+for.body.us:
+  br label %loop_0.cond
+
+loop_0.cond:
+  br i1 true, label %loop_0.ph, label %loop_1.ph
+
+loop_0.ph:
+  br label %loop_0
+
+loop_1.exit:
+  br label %loop_1.ph
+
+loop_1.ph:
+  %c.lcssa = phi i32 [ 0, %loop_0.cond ], [ %val, %loop_1.exit ]
+  br label %loop_1
+
+loop_0:
+  br i1 undef, label %loop_0, label %loop_1.exit
+
+loop_1:
+  %t.1 = phi i32 [ %val, %loop_1 ], [ %c.lcssa, %loop_1.ph ]
+  %d.1 = phi i32 [ %c.lcssa, %loop_1 ], [ %val, %loop_1.ph ]
+  br i1 undef, label %leave, label %loop_1
+
+leave:
+  ret void
+}