Recognize and simplify

(A+B) == A  ->  B == 0
A == (A+B)  ->  B == 0



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124567 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 27 insertions, 1 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index fe436bce21..8c5e7e48c4 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2341,7 +2341,17 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
     if (match(Op1, m_Sub(m_Specific(Op0), m_Value(B))))
       return new ICmpInst(I.getPredicate(), B,
                           Constant::getNullValue(B->getType()));
-    
+
+    // (A+B) == A  ->  B == 0
+    if (match(Op0, m_Add(m_Specific(Op1), m_Value(B))))
+      return new ICmpInst(I.getPredicate(), B,
+                          Constant::getNullValue(B->getType()));
+
+    // A == (A+B)  ->  B == 0
+    if (match(Op1, m_Add(m_Specific(Op0), m_Value(B))))
+      return new ICmpInst(I.getPredicate(), B,
+                          Constant::getNullValue(B->getType()));
+
     // (X&Z) == (Y&Z) -> (X^Y) & Z == 0
     if (Op0->hasOneUse() && Op1->hasOneUse() &&
         match(Op0, m_And(m_Value(A), m_Value(B))) && 
diff --git a/test/Transforms/InstCombine/add.ll b/test/Transforms/InstCombine/add.ll
index 4719809d6d..b3a7f52607 100644
--- a/test/Transforms/InstCombine/add.ll
+++ b/test/Transforms/InstCombine/add.ll
@@ -275,3 +275,19 @@ define i32 @test36(i32 %a) {
 	%q = and i32 %z, 1  ; always zero
 	ret i32 %q
 }
+
+define i32 @test37(i32 %a, i32 %b) nounwind readnone {
+entry:
+  %add = add nsw i32 %a, %b
+  %cmp = icmp eq i32 %add, %a
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+define i32 @test38(i32 %a, i32 %b) nounwind readnone {
+entry:
+  %add = add nsw i32 %a, %b
+  %cmp = icmp eq i32 %add, %a
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}