[PATCH] D121104: [SCEV] Verify all IR -> SCEV mappings

[Nikita Popov via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGba8ee4a43e39: [SCEV] Verify all IR -> SCEV mappings (authored by nikic).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D121104/new/

https://reviews.llvm.org/D121104

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -13355,6 +13355,24 @@
   SmallPtrSet<BasicBlock *, 16> ReachableBlocks;
   getReachableBlocks(ReachableBlocks, F);
 
+  auto GetDelta = [&](const SCEV *Old, const SCEV *New) -> const SCEV * {
+    if (containsUndefs(Old) || containsUndefs(New)) {
+      // SCEV treats "undef" as an unknown but consistent value (i.e. it does
+      // not propagate undef aggressively).  This means we can (and do) fail
+      // verification in cases where a transform makes a value go from "undef"
+      // to "undef+1" (say).  The transform is fine, since in both cases the
+      // result is "undef", but SCEV thinks the value increased by 1.
+      return nullptr;
+    }
+
+    // Unless VerifySCEVStrict is set, we only compare constant deltas.
+    const SCEV *Delta = SE2.getMinusSCEV(Old, New);
+    if (!VerifySCEVStrict && !isa<SCEVConstant>(Delta))
+      return nullptr;
+
+    return Delta;
+  };
+
   while (!LoopStack.empty()) {
     auto *L = LoopStack.pop_back_val();
     llvm::append_range(LoopStack, *L);
@@ -13384,16 +13402,6 @@
       continue;
     }
 
-    if (containsUndefs(CurBECount) || containsUndefs(NewBECount)) {
-      // SCEV treats "undef" as an unknown but consistent value (i.e. it does
-      // not propagate undef aggressively).  This means we can (and do) fail
-      // verification in cases where a transform makes the trip count of a loop
-      // go from "undef" to "undef+1" (say).  The transform is fine, since in
-      // both cases the loop iterates "undef" times, but SCEV thinks we
-      // increased the trip count of the loop by 1 incorrectly.
-      continue;
-    }
-
     if (SE.getTypeSizeInBits(CurBECount->getType()) >
         SE.getTypeSizeInBits(NewBECount->getType()))
       NewBECount = SE2.getZeroExtendExpr(NewBECount, CurBECount->getType());
@@ -13401,10 +13409,8 @@
              SE.getTypeSizeInBits(NewBECount->getType()))
       CurBECount = SE2.getZeroExtendExpr(CurBECount, NewBECount->getType());
 
-    const SCEV *Delta = SE2.getMinusSCEV(CurBECount, NewBECount);
-
-    // Unless VerifySCEVStrict is set, we only compare constant deltas.
-    if ((VerifySCEVStrict || isa<SCEVConstant>(Delta)) && !Delta->isZero()) {
+    const SCEV *Delta = GetDelta(CurBECount, NewBECount);
+    if (Delta && !Delta->isZero()) {
       dbgs() << "Trip Count for " << *L << " Changed!\n";
       dbgs() << "Old: " << *CurBECount << "\n";
       dbgs() << "New: " << *NewBECount << "\n";
@@ -13437,6 +13443,21 @@
              << " is in ValueExprMap but not in ExprValueMap\n";
       std::abort();
     }
+
+    if (auto *I = dyn_cast<Instruction>(&*KV.first)) {
+      if (!ReachableBlocks.contains(I->getParent()))
+        continue;
+      const SCEV *OldSCEV = SCM.visit(KV.second);
+      const SCEV *NewSCEV = SE2.getSCEV(I);
+      const SCEV *Delta = GetDelta(OldSCEV, NewSCEV);
+      if (Delta && !Delta->isZero()) {
+        dbgs() << "SCEV for value " << *I << " changed!\n"
+               << "Old: " << *OldSCEV << "\n"
+               << "New: " << *NewSCEV << "\n"
+               << "Delta: " << *Delta << "\n";
+        std::abort();
+      }
+    }
   }
 
   for (const auto &KV : ExprValueMap) {


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