[JumpThreading][LVI] Invalidate LVI information after blocks are merged

[anna]

Summary

After a single predecessor is merged into a basic block, we need to invalidate
the LVI information for the new merged block, when LVI is not provably true for
all of instructions in the new block.
The test cases added show the correct LVI information using the LVI printer
pass.

[anna]

ping

[davide]

LGTM, thought I already accepted this one.

llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp

if (!TI->isExceptional() && TI->getNumSuccessors() == 1 &&
         SinglePred != BB && !hasAddressTakenAndUsed(BB)) {
       // If SinglePred was a loop header, BB becomes one.
       if (LoopHeaders.erase(SinglePred))
         LoopHeaders.insert(BB);
 
       LVI->eraseBlock(SinglePred);
       MergeBasicBlockIntoOnlyPred(BB);
 
+      // Now that BB is merged into SinglePred (i.e. SinglePred Code followed by
+      // BB code within one basic block `BB`), we need to invalidate the LVI
+      // information associated with BB, because the LVI information need not be
+      // true for all of BB after the merge. For example,
+      // Before the merge, LVI info and code is as follows:
+      // SinglePred: <LVI info1 for %p val>
+      // %y = use of %p
+      // call @exit() // need not transfer execution to successor.
+      // assume(%p) // from this point on %p is true
+      // br label %BB
+      // BB: <LVI info2 for %p val, i.e. %p is true>
+      // %x = use of %p
+      // br label exit
+      //
+      // Note that this LVI info for blocks BB and SinglPred is correct for %p
+      // (info2 and info1 respectively). After the merge and the deletion of the
+      // LVI info1 for SinglePred. We have the following code:
+      // BB: <LVI info2 for %p val>
+      // %y = use of %p
+      // call @exit()
+      // assume(%p)
+      // %x = use of %p <-- LVI info2 is correct from here onwards.
+      // br label exit
+      // LVI info2 for BB is incorrect at the beginning of BB.
+
+      // Invalidate LVI information for BB if the LVI is not provably true for
+      // all of BB.
+      if (any_of(*BB, [](Instruction &I) {
+            return !isGuaranteedToTransferExecutionToSuccessor(&I);
+          }))
+        LVI->eraseBlock(BB);
       return true;
     }
   }
 
   if (TryToUnfoldSelectInCurrBB(BB))
     return true;
 
   // Look if we can propagate guards to predecessors.

llvm/trunk/test/Analysis/LazyValueAnalysis/lvi-after-jumpthreading.ll

 ; CHECK-NEXT:    ; LatticeVal for: '  %cont = and i1 %cont1, %cont2' in BB: '%backedge' is: overdefined
 ; CHECK-NEXT:  %cont = and i1 %cont1, %cont2
   %cont = and i1 %cont1, %cont2
   br i1 %cont, label %loop, label %exit
 
 exit:
   ret i8 0
 }
+
+; Merging cont block into do block. Make sure that we do not incorrectly have the cont
+; LVI info as LVI info for the beginning of do block. LVI info for %i is Range[0,1)
+; at beginning of cont Block, which is incorrect at the beginning of do block.
+define i32 @test3(i32 %i, i1 %f, i32 %n) {
+; CHECK-LABEL: LVI for function 'test3':
+; CHECK-LABEL: entry
+; CHECK:  ; LatticeVal for: 'i32 %i' is: overdefined
+; CHECK: %c = icmp ne i32 %i, -2134 
+; CHECK: br i1 %c, label %cont, label %exit
+entry:
+  %c = icmp ne i32 %i, -2134
+  br i1 %c, label %do, label %exit
+
+exit:
+  %c1 = icmp ne i32 %i, -42
+  br i1 %c1, label %exit2, label %exit
+
+; CHECK-LABEL: cont:
+; Here cont is merged to do and i is any value except -2134.
+; i is not the single value: zero.
+; CHECK-NOT:  ; LatticeVal for: 'i32 %i' is: constantrange<0, 1>
+; CHECK:      ; LatticeVal for: 'i32 %i' is: constantrange<-2133, -2134>
+; CHECK:      ; LatticeVal for: '  %cond.0 = icmp sgt i32 %i, 0' in BB: '%cont' is: overdefined
+; CHECK:   %cond.0 = icmp sgt i32 %i, 0
+; CHECK:   %consume = call i32 @consume
+; CHECK:   %cond = icmp eq i32 %i, 0
+; CHECK:   call void (i1, ...) @llvm.experimental.guard(i1 %cond)
+; CHECK:   %cond.3 = icmp sgt i32 %i, %n
+; CHECK:   br i1 %cond.3, label %exit2, label %exit
+cont:
+  %cond.3 = icmp sgt i32 %i, %n
+  br i1 %cond.3, label %exit2, label %exit
+
+do:
+  %cond.0 = icmp sgt i32 %i, 0
+  %consume = call i32 @consume(i1 %cond.0)
+  %cond = icmp eq i32 %i, 0
+  call void (i1, ...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
+  %cond.2 = icmp sgt i32 %i, 0
+  br i1 %cond.2, label %exit, label %cont
+  
+exit2:
+; CHECK-LABEL: exit2:
+; LatticeVal for: 'i32 %i' is: constantrange<-2134, 1>
+  ret i32 30
+}
+
+; FIXME: We should be able to merge cont into do.
+; When we do so, LVI for cont cannot be the one for the merged do block.
+define i32 @test4(i32 %i, i1 %f, i32 %n) {
+; CHECK-LABEL: LVI for function 'test4':
+entry:
+  %c = icmp ne i32 %i, -2134
+  br i1 %c, label %do, label %exit
+
+exit:                                             ; preds = %do, %cont, %exit, %entry
+  %c1 = icmp ne i32 %i, -42
+  br i1 %c1, label %exit2, label %exit
+
+cont:                                             ; preds = %do
+; CHECK-LABEL: cont:
+; CHECK:  ; LatticeVal for: 'i1 %f' is: constantrange<-1, 0>
+; CHECK: call void @dummy(i1 %f)
+  call void @dummy(i1 %f)
+  br label %exit2
+
+do:                                               ; preds = %entry
+; CHECK-LABEL: do:
+; CHECK:  ; LatticeVal for: 'i1 %f' is: overdefined
+; CHECK: call void @dummy(i1 %f)
+; CHECK: br i1 %cond, label %exit, label %cont
+  call void @dummy(i1 %f)
+  %consume = call i32 @exit()
+  call void @llvm.assume(i1 %f)
+  %cond = icmp eq i1 %f, false
+  br i1 %cond, label %exit, label %cont
+
+exit2:                                            ; preds = %cont, %exit
+  ret i32 30
+}
+
+declare i32 @exit()
+declare i32 @consume(i1)
+declare void @llvm.assume(i1) nounwind
+declare void @dummy(i1) nounwind
+declare void @llvm.experimental.guard(i1, ...)