[CVP]: Fold icmp eq X, C to trunc X to i1 if C=2k+1 and X in [2k, 2k+1]

Author: YanWQ-monad

llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

@@ -332,6 +332,39 @@ static bool constantFoldCmp(CmpInst *Cmp, LazyValueInfo *LVI) {
   return true;
 }
 
+/// Given an icmp `icmp eq X, C`,
+/// if we already know that C is 2k+1 and X is in [2k, 2k+1],
+/// then we can fold it to `trunc X to i1`.
+static bool processEqualityICmp(CmpInst *Cmp, LazyValueInfo *LVI) {
+  if (Cmp->getType()->isVectorTy() ||
+      !Cmp->getOperand(0)->getType()->isIntegerTy() || !Cmp->isEquality())
+    return false;
+
+  Value *Op0 = Cmp->getOperand(0);
+  Value *Op1 = Cmp->getOperand(1);
+  ConstantInt *CI = dyn_cast<ConstantInt>(Op1);
+  if (!CI)
+    return false;
+
+  ConstantRange Range =
+      LVI->getConstantRangeAtUse(Cmp->getOperandUse(0), /*UndefAllowed*/ true);
+  APInt RangeSize = Range.getUpper() - Range.getLower();
+  APInt Value = CI->getValue();
+  if (RangeSize != 2 || !Range.contains(Value))
+    return false;
+
+  bool ShouldBeOdd = Cmp->getPredicate() == ICmpInst::Predicate::ICMP_EQ;
+  if ((CI->getValue() & 1) == ShouldBeOdd) {
+    IRBuilder<> B{Cmp};
+    auto *Trunc = B.CreateTruncOrBitCast(Op0, Cmp->getType());
+    Cmp->replaceAllUsesWith(Trunc);
+    Cmp->eraseFromParent();
+    return true;
+  }
+
+  return false;
+}
+
 static bool processCmp(CmpInst *Cmp, LazyValueInfo *LVI) {
   if (constantFoldCmp(Cmp, LVI))
     return true;
@@ -340,6 +373,9 @@ static bool processCmp(CmpInst *Cmp, LazyValueInfo *LVI) {
     if (processICmp(ICmp, LVI))
       return true;
 
+  if (processEqualityICmp(Cmp, LVI))
+      return true;
+
   return false;
 }
 

llvm/test/Transforms/CorrelatedValuePropagation/icmp.ll

@@ -614,10 +614,10 @@ define void @test_cmp_phi(i8 %a) {
 ; CHECK-NEXT:    br i1 [[C0]], label [[LOOP:%.*]], label [[EXIT:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[P:%.*]] = phi i8 [ [[A]], [[ENTRY:%.*]] ], [ [[B:%.*]], [[LOOP]] ]
-; CHECK-NEXT:    [[C1:%.*]] = icmp ne i8 [[P]], 0
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i8 [[P]] to i1
 ; CHECK-NEXT:    [[C4:%.*]] = call i1 @get_bool()
 ; CHECK-NEXT:    [[B]] = zext i1 [[C4]] to i8
-; CHECK-NEXT:    br i1 [[C1]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    br i1 [[TMP0]], label [[LOOP]], label [[EXIT]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -1484,7 +1484,7 @@ define i1 @test_icmp_eq_on_valid_bool_range(i8 %x) {
 ; CHECK-NEXT:    [[TMP2:%.*]] = tail call i1 @get_bool()
 ; CHECK-NEXT:    br label [[BB3:%.*]]
 ; CHECK:       bb1:
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i8 [[X]], 1
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i8 [[X]] to i1
 ; CHECK-NEXT:    br label [[BB3]]
 ; CHECK:       bb3:
 ; CHECK-NEXT:    [[TMP4:%.*]] = phi i1 [ [[TMP3]], [[BB1]] ], [ [[TMP2]], [[BB2]] ]
@@ -1514,7 +1514,7 @@ define i1 @test_icmp_ne_on_valid_bool_range(i8 %x) {
 ; CHECK-NEXT:    [[TMP2:%.*]] = tail call i1 @get_bool()
 ; CHECK-NEXT:    br label [[BB3:%.*]]
 ; CHECK:       bb1:
-; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i8 [[X]], 0
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc i8 [[X]] to i1
 ; CHECK-NEXT:    br label [[BB3]]
 ; CHECK:       bb3:
 ; CHECK-NEXT:    [[TMP4:%.*]] = phi i1 [ [[TMP3]], [[BB1]] ], [ [[TMP2]], [[BB2]] ]

llvm/test/Transforms/JumpThreading/pr33917.ll

@@ -15,16 +15,16 @@ define void @patatino() personality ptr @rust_eh_personality {
 ; CHECK-LABEL: @patatino(
 ; CHECK-NEXT:  bb9:
 ; CHECK-NEXT:    [[T9:%.*]] = invoke ptr @foo()
-; CHECK-NEXT:    to label [[GOOD:%.*]] unwind label [[BAD:%.*]]
+; CHECK-NEXT:            to label [[GOOD:%.*]] unwind label [[BAD:%.*]]
 ; CHECK:       bad:
 ; CHECK-NEXT:    [[T10:%.*]] = landingpad { ptr, i32 }
-; CHECK-NEXT:    cleanup
+; CHECK-NEXT:            cleanup
 ; CHECK-NEXT:    resume { ptr, i32 } [[T10]]
 ; CHECK:       good:
 ; CHECK-NEXT:    [[T11:%.*]] = icmp ne ptr [[T9]], null
 ; CHECK-NEXT:    [[T12:%.*]] = zext i1 [[T11]] to i64
-; CHECK-NEXT:    [[COND:%.*]] = icmp eq i64 [[T12]], 1
-; CHECK-NEXT:    br i1 [[COND]], label [[IF_TRUE:%.*]], label [[DONE:%.*]]
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i64 [[T12]] to i1
+; CHECK-NEXT:    br i1 [[TMP0]], label [[IF_TRUE:%.*]], label [[DONE:%.*]]
 ; CHECK:       if_true:
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[T11]])
 ; CHECK-NEXT:    br label [[DONE]]