[LoopDeletion] Clear SCEV loop dispositions

`Loop::makeLoopInvariant` can hoist instructions out of loops, so loop
dispositions for the loop it operated on may need to be cleared.  We can
be smarter here (especially around how `forgetLoopDispositions` is
implemented), but let's be correct first.

Fixes PR27570.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268406 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LoopDeletion.cpp

@@ -44,10 +44,10 @@ namespace {
     }
 
   private:
-    bool isLoopDead(Loop *L, SmallVectorImpl<BasicBlock *> &exitingBlocks,
-                    SmallVectorImpl<BasicBlock *> &exitBlocks,
-                    bool &Changed, BasicBlock *Preheader);
-
+    bool isLoopDead(Loop *L, ScalarEvolution &SE,
+                    SmallVectorImpl<BasicBlock *> &exitingBlocks,
+                    SmallVectorImpl<BasicBlock *> &exitBlocks, bool &Changed,
+                    BasicBlock *Preheader);
   };
 }
 
@@ -65,7 +65,7 @@ Pass *llvm::createLoopDeletionPass() {
 /// isLoopDead - Determined if a loop is dead.  This assumes that we've already
 /// checked for unique exit and exiting blocks, and that the code is in LCSSA
 /// form.
-bool LoopDeletion::isLoopDead(Loop *L,
+bool LoopDeletion::isLoopDead(Loop *L, ScalarEvolution &SE,
                               SmallVectorImpl<BasicBlock *> &exitingBlocks,
                               SmallVectorImpl<BasicBlock *> &exitBlocks,
                               bool &Changed, BasicBlock *Preheader) {
@@ -77,6 +77,8 @@ bool LoopDeletion::isLoopDead(Loop *L,
   // sufficient to guarantee that no loop-variant values are used outside
   // of the loop.
   BasicBlock::iterator BI = exitBlock->begin();
+  bool AllEntriesInvariant = true;
+  bool AllOutgoingValuesSame = true;
   while (PHINode *P = dyn_cast<PHINode>(BI)) {
     Value *incoming = P->getIncomingValueForBlock(exitingBlocks[0]);
 
@@ -85,17 +87,30 @@ bool LoopDeletion::isLoopDead(Loop *L,
     // blocks, then it is impossible to statically determine which value should
     // be used.
     for (unsigned i = 1, e = exitingBlocks.size(); i < e; ++i) {
-      if (incoming != P->getIncomingValueForBlock(exitingBlocks[i]))
-        return false;
+      if (incoming != P->getIncomingValueForBlock(exitingBlocks[i])) {
+        AllOutgoingValuesSame = false;
+        break;
+      }
     }
 
+    if (!AllOutgoingValuesSame)
+      break;
+
     if (Instruction *I = dyn_cast<Instruction>(incoming))
-      if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator()))
-        return false;
+      if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) {
+        AllEntriesInvariant = false;
+        break;
+      }
 
     ++BI;
   }
 
+  if (Changed)
+    SE.forgetLoopDispositions(L);
+
+  if (!AllEntriesInvariant || !AllOutgoingValuesSame)
+    return false;
+
   // Make sure that no instructions in the block have potential side-effects.
   // This includes instructions that could write to memory, and loads that are
   // marked volatile.  This could be made more aggressive by using aliasing
@@ -153,14 +168,15 @@ bool LoopDeletion::runOnLoop(Loop *L, LPPassManager &) {
   if (exitBlocks.size() != 1)
     return false;
 
+  ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+
   // Finally, we have to check that the loop really is dead.
   bool Changed = false;
-  if (!isLoopDead(L, exitingBlocks, exitBlocks, Changed, preheader))
+  if (!isLoopDead(L, SE, exitingBlocks, exitBlocks, Changed, preheader))
     return Changed;
 
   // Don't remove loops for which we can't solve the trip count.
   // They could be infinite, in which case we'd be changing program behavior.
-  ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
   const SCEV *S = SE.getMaxBackedgeTakenCount(L);
   if (isa<SCEVCouldNotCompute>(S))
     return Changed;

test/Transforms/LoopDeletion/update-scev.ll

@@ -0,0 +1,56 @@
+; RUN: opt -S -analyze -scalar-evolution -loop-deletion -scalar-evolution < %s | FileCheck %s --check-prefix=SCEV-EXPRS
+; RUN: opt -S -loop-deletion < %s | FileCheck %s --check-prefix=IR-AFTER-TRANSFORM
+; RUN: opt -S -indvars -loop-deletion -indvars < %s | FileCheck %s --check-prefix=ORIGINAL-CRASH
+
+; Checking for a crash.  Loop-deletion would change the loop
+; disposition of an instruction, but not update SCEV.
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.11.0"
+
+define void @pr27570() {
+; IR-AFTER-TRANSFORM-LABEL: @pr27570(
+; ORIGINAL-CRASH: @pr27570(
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond14, %entry
+  %f.0 = phi i32 [ 20, %entry ], [ 0, %for.cond14 ]
+  br label %for.body
+
+for.body:                                         ; preds = %for.inc11, %for.cond
+; IR-AFTER-TRANSFORM: for.body:
+; IR-AFTER-TRANSFORM: %cmp = icmp eq i32 %val, -1
+; IR-AFTER-TRANSFORM: %conv7 = zext i1 %cmp to i32
+; IR-AFTER-TRANSFORM: for.body6:
+
+; SCEV-EXPRS:  %conv7 = zext i1 %cmp to i32
+; SCEV-EXPRS:  %conv7 = zext i1 %cmp to i32
+; SCEV-EXPRS-NEXT:  -->  {{.*}} LoopDispositions: { %for.body: Variant, %for.cond: Variant, %for.body6: Invariant }
+  %val = phi i32 [ -20, %for.cond ], [ %inc12, %for.inc11 ]
+  %g.040 = phi i32 [ -20, %for.cond ], [ %and.lcssa, %for.inc11 ]
+  br label %for.body6
+
+for.body6:                                        ; preds = %for.body6, %for.body
+  %h.039 = phi i32 [ 1, %for.body ], [ %inc, %for.body6 ]
+  %g.138 = phi i32 [ %g.040, %for.body ], [ %and, %for.body6 ]
+  %cmp = icmp eq i32 %val, -1
+  %conv7 = zext i1 %cmp to i32
+  %add.i = add nsw i32 %conv7, %h.039
+  %sext = shl i32 %add.i, 24
+  %conv8 = ashr exact i32 %sext, 24
+  %cmp9 = icmp eq i32 %conv8, %f.0
+  %conv10 = zext i1 %cmp9 to i32
+  %and = and i32 %conv10, %g.138
+  %inc = add i32 %h.039, 1
+  br i1 undef, label %for.inc11, label %for.body6
+
+for.inc11:                                        ; preds = %for.body6
+  %and.lcssa = phi i32 [ %and, %for.body6 ]
+  %inc12 = add nsw i32 %val, 1
+  %tobool = icmp eq i32 %inc12, 0
+  br i1 %tobool, label %for.cond14, label %for.body
+
+for.cond14:                                       ; preds = %for.cond14, %for.inc11
+  br i1 undef, label %for.cond, label %for.cond14
+}