[ValueTracking] Handle icmp pred (trunc X), C in computeKnownBitsFromCmp

Author: dtcxzyw

llvm/lib/Analysis/ValueTracking.cpp

@@ -708,6 +708,25 @@ static void computeKnownBitsFromCmp(const Value *V, CmpInst::Predicate Pred,
   }
 }
 
+static void computeKnownBitsFromICmpCond(const Value *V, ICmpInst *Cmp,
+                                         KnownBits &Known,
+                                         const SimplifyQuery &SQ, bool Invert) {
+  ICmpInst::Predicate Pred =
+      Invert ? Cmp->getInversePredicate() : Cmp->getPredicate();
+  Value *LHS = Cmp->getOperand(0);
+  Value *RHS = Cmp->getOperand(1);
+
+  // Handle icmp pred (trunc V), C
+  if (match(LHS, m_Trunc(m_Specific(V)))) {
+    KnownBits DstKnown(LHS->getType()->getScalarSizeInBits());
+    computeKnownBitsFromCmp(LHS, Pred, LHS, RHS, DstKnown, SQ);
+    Known = Known.unionWith(DstKnown.anyext(Known.getBitWidth()));
+    return;
+  }
+
+  computeKnownBitsFromCmp(V, Pred, LHS, RHS, Known, SQ);
+}
+
 static void computeKnownBitsFromCond(const Value *V, Value *Cond,
                                      KnownBits &Known, unsigned Depth,
                                      const SimplifyQuery &SQ, bool Invert) {
@@ -727,9 +746,7 @@ static void computeKnownBitsFromCond(const Value *V, Value *Cond,
   }
 
   if (auto *Cmp = dyn_cast<ICmpInst>(Cond))
-    computeKnownBitsFromCmp(
-        V, Invert ? Cmp->getInversePredicate() : Cmp->getPredicate(),
-        Cmp->getOperand(0), Cmp->getOperand(1), Known, SQ);
+    computeKnownBitsFromICmpCond(V, Cmp, Known, SQ, Invert);
 }
 
 void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
@@ -815,8 +832,7 @@ void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known,
     if (!isValidAssumeForContext(I, Q.CxtI, Q.DT))
       continue;
 
-    computeKnownBitsFromCmp(V, Cmp->getPredicate(), Cmp->getOperand(0),
-                            Cmp->getOperand(1), Known, Q);
+    computeKnownBitsFromICmpCond(V, Cmp, Known, Q, /*Invert=*/false);
   }
 
   // Conflicting assumption: Undefined behavior will occur on this execution
@@ -9133,7 +9149,7 @@ addValueAffectedByCondition(Value *V,
 
     // Peek through unary operators to find the source of the condition.
     Value *Op;
-    if (match(I, m_PtrToInt(m_Value(Op)))) {
+    if (match(I, m_CombineOr(m_PtrToInt(m_Value(Op)), m_Trunc(m_Value(Op))))) {
       if (isa<Instruction>(Op) || isa<Argument>(Op))
         InsertAffected(Op);
     }

llvm/test/Transforms/InstCombine/known-bits.ll

@@ -350,8 +350,7 @@ define i32 @test_icmp_trunc1(i32 %x){
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[Y]], 7
 ; CHECK-NEXT:    br i1 [[CMP]], label [[THEN:%.*]], label [[ELSE:%.*]]
 ; CHECK:       then:
-; CHECK-NEXT:    [[Z:%.*]] = and i32 [[X]], 15
-; CHECK-NEXT:    ret i32 [[Z]]
+; CHECK-NEXT:    ret i32 7
 ; CHECK:       else:
 ; CHECK-NEXT:    ret i32 0
 ;
@@ -372,8 +371,7 @@ define i32 @test_icmp_trunc_assume(i32 %x){
 ; CHECK-NEXT:    [[Y:%.*]] = trunc i32 [[X:%.*]] to i16
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[Y]], 7
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]])
-; CHECK-NEXT:    [[Z:%.*]] = and i32 [[X]], 15
-; CHECK-NEXT:    ret i32 [[Z]]
+; CHECK-NEXT:    ret i32 7
 ;
 entry:
   %y = trunc i32 %x to i16
@@ -389,9 +387,8 @@ define i64 @test_icmp_trunc2(i64 %x) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[CONV]], 12
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[SEXT:%.*]] = shl i64 [[X]], 32
-; CHECK-NEXT:    [[RET:%.*]] = ashr exact i64 [[SEXT]], 32
-; CHECK-NEXT:    ret i64 [[RET]]
+; CHECK-NEXT:    [[SEXT:%.*]] = and i64 [[X]], 2147483647
+; CHECK-NEXT:    ret i64 [[SEXT]]
 ; CHECK:       if.else:
 ; CHECK-NEXT:    ret i64 0
 ;
@@ -414,7 +411,7 @@ define i64 @test_icmp_trunc3(i64 %n) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[CONV]], 96
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[RET:%.*]] = and i64 [[N]], 4294967295
+; CHECK-NEXT:    [[RET:%.*]] = and i64 [[N]], 127
 ; CHECK-NEXT:    ret i64 [[RET]]
 ; CHECK:       if.else:
 ; CHECK-NEXT:    ret i64 0
@@ -439,7 +436,7 @@ define i8 @test_icmp_trunc4(i64 %n) {
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
 ; CHECK-NEXT:    [[CONV2:%.*]] = trunc i64 [[N]] to i8
-; CHECK-NEXT:    [[ADD:%.*]] = add i8 [[CONV2]], 48
+; CHECK-NEXT:    [[ADD:%.*]] = or disjoint i8 [[CONV2]], 48
 ; CHECK-NEXT:    ret i8 [[ADD]]
 ; CHECK:       if.else:
 ; CHECK-NEXT:    ret i8 0
@@ -465,8 +462,8 @@ define i64 @test_icmp_trunc5(i64 %n) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[CONV1]], -13
 ; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
 ; CHECK:       if.then:
-; CHECK-NEXT:    [[AND:%.*]] = and i64 [[SHR]], 4294967295
-; CHECK-NEXT:    [[NOT:%.*]] = xor i64 [[AND]], 4294967295
+; CHECK-NEXT:    [[TMP0:%.*]] = and i64 [[SHR]], 15
+; CHECK-NEXT:    [[NOT:%.*]] = xor i64 [[TMP0]], 15
 ; CHECK-NEXT:    ret i64 [[NOT]]
 ; CHECK:       if.else:
 ; CHECK-NEXT:    ret i64 13