[InstSimplify] restrict icmp fold with 2 sdiv exact operands (PR32949)

These folds were introduced with https://reviews.llvm.org/rL127064 as part of solving:
https://bugs.llvm.org/show_bug.cgi?id=9343

As shown here:
http://rise4fun.com/Alive/C8
...however, the sdiv exact case needs a stronger predicate.

I opted for duplicated code instead of adding another fallthrough because I think that's 
easier to read (and edit in case we need/want to restrict/loosen the predicates any more).

This should fix:
https://bugs.llvm.org/show_bug.cgi?id=32949
https://bugs.llvm.org/show_bug.cgi?id=32948

Differential Revision: https://reviews.llvm.org/D32954

llvm-svn: 303104

1 files changed, 11 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 6293c2a08a1..5728887cc1e 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -2827,10 +2827,19 @@ static Value *simplifyICmpWithBinOp(CmpInst::Predicate Pred, Value *LHS,
       break;
     case Instruction::UDiv:
     case Instruction::LShr:
-      if (ICmpInst::isSigned(Pred))
+      if (ICmpInst::isSigned(Pred) || !LBO->isExact() || !RBO->isExact())
         break;
-      LLVM_FALLTHROUGH;
+      if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
+                                      RBO->getOperand(0), Q, MaxRecurse - 1))
+          return V;
+      break;
     case Instruction::SDiv:
+      if (!ICmpInst::isEquality(Pred) || !LBO->isExact() || !RBO->isExact())
+        break;
+      if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
+                                      RBO->getOperand(0), Q, MaxRecurse - 1))
+        return V;
+      break;
     case Instruction::AShr:
       if (!LBO->isExact() || !RBO->isExact())
         break;