[InstCombine] foldICmpBinOp(): consider inverted check in 'unsigned add overflow' check

A follow-up for r342004.
This will be changed to produce @llvm.add.with.overflow in a later patch,
but for now just make things more consistent overall.

https://rise4fun.com/Alive/qxE

Name: (Op1 + X) u< Op1 --> ~Op1 u< X
  %t0 = add i8 %Op1, %X
  %r = icmp ult i8 %t0, %Op1
=>
  %n = xor i8 %Op1, -1
  %r = icmp ult i8 %n, %X

Name: (Op1 + X) u>= Op1 --> ~Op1 u>= X
  %t0 = add i8 %Op1, %X
  %r = icmp uge i8 %t0, %Op1
=>
  %n = xor i8 %Op1, -1
  %r = icmp uge i8 %n, %X

;-------------------------------------------------------------------------------

Name: Op0 u> (Op0 + X) --> X u> ~Op0
  %t0 = add i8 %Op0, %X
  %r = icmp ugt i8 %Op0, %t0
=>
  %n = xor i8 %Op0, -1
  %r = icmp ugt i8 %X, %n

Name: Op0 u<= (Op0 + X) --> X u<= ~Op0
  %t0 = add i8 %Op0, %X
  %r = icmp ule i8 %Op0, %t0
=>
  %n = xor i8 %Op0, -1
  %r = icmp ule i8 %X, %n

llvm-svn: 371100

1 files changed, 4 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 8cb0a26cfe3..65c0d2df4f2 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3609,13 +3609,13 @@ Instruction *InstCombiner::foldICmpBinOp(ICmpInst &I) {
   Value *X;
 
   // Convert add-with-unsigned-overflow comparisons into a 'not' with compare.
-  // (Op1 + X) <u Op1 --> ~Op1 <u X
-  // Op0 >u (Op0 + X) --> X >u ~Op0
+  // (Op1 + X) u</u>= Op1 --> ~Op1 u</u>= X
   if (match(Op0, m_OneUse(m_c_Add(m_Specific(Op1), m_Value(X)))) &&
-      Pred == ICmpInst::ICMP_ULT)
+      (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_UGE))
     return new ICmpInst(Pred, Builder.CreateNot(Op1), X);
+  // Op0 u>/u<= (Op0 + X) --> X u>/u<= ~Op0
   if (match(Op1, m_OneUse(m_c_Add(m_Specific(Op0), m_Value(X)))) &&
-      Pred == ICmpInst::ICMP_UGT)
+      (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_ULE))
     return new ICmpInst(Pred, X, Builder.CreateNot(Op0));
 
   bool NoOp0WrapProblem = false, NoOp1WrapProblem = false;