Apply transformation

Author: leewei05

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -7687,6 +7687,30 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
   if (Instruction *Res = foldReductionIdiom(I, Builder, DL))
     return Res;
 
+  {
+    Value *A;
+    const APInt *C1, *C2;
+    ICmpInst::Predicate PredEq = ICmpInst::ICMP_EQ;
+    if (I.getPredicate() == PredEq) {
+      // c2 must be positive
+      // sext(a) & c1 == c2 --> a & c3 == trunc(c2)
+      if (match(Op0, m_And(m_SExtLike(m_Value(A)), m_APInt(C1))) && match(Op1, m_APInt(C2))) {
+        if (C2->isNonNegative()) {
+          Type *InputTy = A->getType();
+          unsigned TargetBitSize = InputTy->getScalarSizeInBits();
+          // Count the number of 1s in C1 high bits of size TargetBitSize.
+          unsigned Leading1sCount = C1->lshr(C1->getBitWidth() - TargetBitSize).popcount();
+          APInt TruncC1 = C1->trunc(TargetBitSize);
+          if (Leading1sCount > 0) {
+            TruncC1.setBit(TargetBitSize - 1);
+          }
+          Value *AndInst = Builder.CreateAnd(A, TruncC1);
+          return new ICmpInst(PredEq, AndInst, ConstantInt::get(InputTy, C2->trunc(TargetBitSize)));
+        }
+      }
+    }
+  }
+
   return Changed ? &I : nullptr;
 }
 

llvm/test/Transforms/InstCombine/sext-and.ll

@@ -6,9 +6,8 @@ declare void @use(i8)
 define i1 @fold_sext_to_and(i8 %x) {
 ; CHECK-LABEL: define i1 @fold_sext_to_and(
 ; CHECK-SAME: i8 [[X:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = sext i8 [[X]] to i32
-; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[TMP1]], -2147483647
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[TMP2]], 1
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X]], -127
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i8 [[TMP1]], 1
 ; CHECK-NEXT:    ret i1 [[TMP3]]
 ;
   %1 = sext i8 %x to i32
@@ -22,8 +21,8 @@ define i1 @fold_sext_to_and_multi_use(i8 %x) {
 ; CHECK-SAME: i8 [[X:%.*]]) {
 ; CHECK-NEXT:    [[TMP1:%.*]] = sext i8 [[X]] to i32
 ; CHECK-NEXT:    call void @use(i32 [[TMP1]])
-; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[TMP1]], -2147483647
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[TMP2]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = and i8 [[X]], -127
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i8 [[TMP2]], 1
 ; CHECK-NEXT:    ret i1 [[TMP3]]
 ;
   %1 = sext i8 %x to i32
@@ -37,11 +36,8 @@ define i1 @fold_sext_to_and_multi_use(i8 %x) {
 
 define i1 @fold_sext_to_and_wrong(i8 %x) {
 ; CHECK-LABEL: define i1 @fold_sext_to_and_wrong(
-; CHECK-SAME: i2 [[X:%.*]]) {
-; CHECK-NEXT:    [[TMP1:%.*]] = sext i2 [[X]] to i32
-; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[TMP1]], -2147483647
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i32 [[TMP2]], 1
-; CHECK-NEXT:    ret i1 [[TMP3]]
+; CHECK-SAME: i8 [[X:%.*]]) {
+; CHECK-NEXT:    ret i1 false
 ;
   %1 = sext i8 %x to i32
   %2 = and i32 %1, -2147483647