commit 764b0fd5a37168313cd7f8d82753b10392ff2b2b
author Philip Reames <listmail@philipreames.com> Wed Aug 21 15:51:57 2019 +0000
committer Philip Reames <listmail@philipreames.com> Wed Aug 21 15:51:57 2019 +0000
tree f41591c35127ad319972ccc800e101ae9da15479
parent f64918d092c078304f9b25c0ee6f456a39474e31

[instcombine] icmp eq/ne (sub C, Y), C -> icmp eq/ne Y, 0

Noticed while looking at pr43028.  

llvm-svn: 369541

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 5e0a3c3..952f295 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2411,6 +2411,11 @@
   const APInt *C2;
   APInt SubResult;
 
+  // icmp eq/ne (sub C, Y), C -> icmp eq/ne Y, 0
+  if (match(X, m_APInt(C2)) && *C2 == C && Cmp.isEquality())
+    return new ICmpInst(Cmp.getPredicate(), Y,
+                        ConstantInt::get(Y->getType(), 0));
+
   // (icmp P (sub nuw|nsw C2, Y), C) -> (icmp swap(P) Y, C2-C)
   if (match(X, m_APInt(C2)) &&
       ((Cmp.isUnsigned() && Sub->hasNoUnsignedWrap()) ||