From 0b7b446a406be2e7d28460d17de4746b47543691 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Fri, 16 Oct 2020 16:06:14 +0100
Subject: [PATCH] [InstCombine] Support vectors-with-undef in
 and(logicalshift(1,X),1) --> zext(X == 0) fold

---
 .../Transforms/InstCombine/InstCombineAndOrXor.cpp    | 19 ++++++++++---------
 llvm/test/Transforms/InstCombine/and2.ll              |  8 ++++----
 2 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index b9b73a4..11cfa4a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1764,17 +1764,18 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
     return replaceInstUsesWith(I, V);
 
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
+
+  Value *X, *Y;
+  if (match(Op0, m_OneUse(m_LogicalShift(m_One(), m_Value(X)))) &&
+      match(Op1, m_One())) {
+    // (1 << X) & 1 --> zext(X == 0)
+    // (1 >> X) & 1 --> zext(X == 0)
+    Value *IsZero = Builder.CreateICmpEQ(X, ConstantInt::get(Ty, 0));
+    return new ZExtInst(IsZero, Ty);
+  }
+
   const APInt *C;
   if (match(Op1, m_APInt(C))) {
-    Value *X, *Y;
-    if (match(Op0, m_OneUse(m_LogicalShift(m_One(), m_Value(X)))) &&
-        C->isOneValue()) {
-      // (1 << X) & 1 --> zext(X == 0)
-      // (1 >> X) & 1 --> zext(X == 0)
-      Value *IsZero = Builder.CreateICmpEQ(X, ConstantInt::get(Ty, 0));
-      return new ZExtInst(IsZero, Ty);
-    }
-
     const APInt *XorC;
     if (match(Op0, m_OneUse(m_Xor(m_Value(X), m_APInt(XorC))))) {
       // (X ^ C1) & C2 --> (X & C2) ^ (C1&C2)
diff --git a/llvm/test/Transforms/InstCombine/and2.ll b/llvm/test/Transforms/InstCombine/and2.ll
index 6cf71ee..47b0d2d 100644
--- a/llvm/test/Transforms/InstCombine/and2.ll
+++ b/llvm/test/Transforms/InstCombine/and2.ll
@@ -137,8 +137,8 @@ define <2 x i8> @and1_shl1_is_cmp_eq_0_vec(<2 x i8> %x) {
 
 define <2 x i8> @and1_shl1_is_cmp_eq_0_vec_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @and1_shl1_is_cmp_eq_0_vec_undef(
-; CHECK-NEXT:    [[SH:%.*]] = shl <2 x i8> <i8 1, i8 undef>, [[X:%.*]]
-; CHECK-NEXT:    [[AND:%.*]] = and <2 x i8> [[SH]], <i8 1, i8 undef>
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq <2 x i8> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    [[AND:%.*]] = zext <2 x i1> [[TMP1]] to <2 x i8>
 ; CHECK-NEXT:    ret <2 x i8> [[AND]]
 ;
   %sh = shl <2 x i8> <i8 1, i8 undef>, %x
@@ -189,8 +189,8 @@ define <2 x i8> @and1_lshr1_is_cmp_eq_0_vec(<2 x i8> %x) {
 
 define <2 x i8> @and1_lshr1_is_cmp_eq_0_vec_undef(<2 x i8> %x) {
 ; CHECK-LABEL: @and1_lshr1_is_cmp_eq_0_vec_undef(
-; CHECK-NEXT:    [[SH:%.*]] = lshr <2 x i8> <i8 1, i8 undef>, [[X:%.*]]
-; CHECK-NEXT:    [[AND:%.*]] = and <2 x i8> [[SH]], <i8 1, i8 undef>
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq <2 x i8> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    [[AND:%.*]] = zext <2 x i1> [[TMP1]] to <2 x i8>
 ; CHECK-NEXT:    ret <2 x i8> [[AND]]
 ;
   %sh = lshr <2 x i8> <i8 1, i8 undef>, %x
-- 
2.7.4