[InstSimplify] Odd - X ==/!= X -> false/true

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D132989

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 8b08d7c..aad8acf 100644 (file)
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3126,6 +3126,17 @@ static Value *simplifyICmpWithBinOpOnLHS(CmpInst::Predicate Pred,
       return getTrue(ITy);
   }
 
+  // (sub C, X) == X, C is odd  --> false
+  // (sub C, X) != X, C is odd  --> true
+  if (match(LBO, m_Sub(m_APInt(C), m_Specific(RHS)))) {
+    if ((*C & 1) == 1) {
+      if (Pred == CmpInst::ICMP_EQ)
+        return ConstantInt::getFalse(getCompareTy(RHS));
+      if (Pred == CmpInst::ICMP_NE)
+        return ConstantInt::getTrue(getCompareTy(RHS));
+    }
+  }
+
   return nullptr;
 }
 

diff --git a/llvm/test/Transforms/InstSimplify/icmp.ll b/llvm/test/Transforms/InstSimplify/icmp.ll
index b967198..c6d2f3c 100644 (file)
--- a/llvm/test/Transforms/InstSimplify/icmp.ll
+++ b/llvm/test/Transforms/InstSimplify/icmp.ll
@@ -214,9 +214,7 @@ loop:
 
 define i1 @sub_false(i32 %x) {
 ; CHECK-LABEL: @sub_false(
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 1, [[X:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[SUB]], [[X]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
   %sub = sub i32 1, %x
   %cmp = icmp eq i32 %sub, %x
@@ -225,9 +223,7 @@ define i1 @sub_false(i32 %x) {
 
 define i1 @sub_swap(i8 %x) {
 ; CHECK-LABEL: @sub_swap(
-; CHECK-NEXT:    [[SUB:%.*]] = sub i8 3, [[X:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[X]], [[SUB]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 true
 ;
   %sub = sub i8 3, %x
   %cmp = icmp ne i8 %x, %sub
@@ -236,9 +232,7 @@ define i1 @sub_swap(i8 %x) {
 
 define <2 x i1> @sub_odd(<2 x i8> %x) {
 ; CHECK-LABEL: @sub_odd(
-; CHECK-NEXT:    [[SUB:%.*]] = sub <2 x i8> <i8 3, i8 3>, [[X:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne <2 x i8> [[SUB]], [[X]]
-; CHECK-NEXT:    ret <2 x i1> [[CMP]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %sub = sub <2 x i8> <i8 3, i8 3>, %x
   %cmp = icmp ne <2 x i8> %sub, %x