[llvm] [ConstantRange] Handle `Intrinsic::cttz` (PR #67917)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Sat Nov 4 08:40:35 PDT 2023
https://github.com/dtcxzyw updated https://github.com/llvm/llvm-project/pull/67917
>From 8860c068175d7070991c255ea73d6449e03a4222 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Sat, 4 Nov 2023 22:16:38 +0800
Subject: [PATCH] [ConstantRange] Handle `Intrinsic::cttz`
---
llvm/include/llvm/IR/ConstantRange.h | 4 +
llvm/lib/IR/ConstantRange.cpp | 76 +++++++++++++++++++
.../CorrelatedValuePropagation/range.ll | 3 +-
llvm/unittests/IR/ConstantRangeTest.cpp | 14 ++++
4 files changed, 95 insertions(+), 2 deletions(-)
diff --git a/llvm/include/llvm/IR/ConstantRange.h b/llvm/include/llvm/IR/ConstantRange.h
index ca36732e4e2e8c2..efbbb6c99bff792 100644
--- a/llvm/include/llvm/IR/ConstantRange.h
+++ b/llvm/include/llvm/IR/ConstantRange.h
@@ -530,6 +530,10 @@ class [[nodiscard]] ConstantRange {
/// ignoring a possible zero value contained in the input range.
ConstantRange ctlz(bool ZeroIsPoison = false) const;
+ /// Calculate cttz range. If \p ZeroIsPoison is set, the range is computed
+ /// ignoring a possible zero value contained in the input range.
+ ConstantRange cttz(bool ZeroIsPoison = false) const;
+
/// Represents whether an operation on the given constant range is known to
/// always or never overflow.
enum class OverflowResult {
diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 3d71b20f7e853e0..a39dbac28f1a306 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -949,6 +949,7 @@ bool ConstantRange::isIntrinsicSupported(Intrinsic::ID IntrinsicID) {
case Intrinsic::smax:
case Intrinsic::abs:
case Intrinsic::ctlz:
+ case Intrinsic::cttz:
return true;
default:
return false;
@@ -986,6 +987,12 @@ ConstantRange ConstantRange::intrinsic(Intrinsic::ID IntrinsicID,
assert(ZeroIsPoison->getBitWidth() == 1 && "Must be boolean");
return Ops[0].ctlz(ZeroIsPoison->getBoolValue());
}
+ case Intrinsic::cttz: {
+ const APInt *ZeroIsPoison = Ops[1].getSingleElement();
+ assert(ZeroIsPoison && "Must be known (immarg)");
+ assert(ZeroIsPoison->getBitWidth() == 1 && "Must be boolean");
+ return Ops[0].cttz(ZeroIsPoison->getBoolValue());
+ }
default:
assert(!isIntrinsicSupported(IntrinsicID) && "Shouldn't be supported");
llvm_unreachable("Unsupported intrinsic");
@@ -1736,6 +1743,75 @@ ConstantRange ConstantRange::ctlz(bool ZeroIsPoison) const {
APInt(getBitWidth(), getUnsignedMin().countl_zero() + 1));
}
+static ConstantRange getUnsignedCountTrailingZerosRange(const APInt &Lower,
+ const APInt &Upper) {
+ assert(!ConstantRange(Lower, Upper).isWrappedSet() &&
+ "Unexpected wrapped set.");
+ assert(Lower != Upper && "Unexpected empty set.");
+ unsigned BitWidth = Lower.getBitWidth();
+ if (Lower + 1 == Upper)
+ return ConstantRange(APInt(BitWidth, Lower.countr_zero()));
+ if (Lower.isZero())
+ return ConstantRange(APInt::getZero(BitWidth),
+ APInt(BitWidth, BitWidth + 1));
+
+ // Calculate longest common prefix.
+ unsigned LCPLength = (Lower ^ (Upper - 1)).countl_zero();
+ // If Lower is {LCP, 000...}, the maximum is Lower.countr_zero().
+ // Otherwise, the maximum is BitWidth - LCPLength - 1 ({LCP, 100...}).
+ return ConstantRange(
+ APInt::getZero(BitWidth),
+ APInt(BitWidth,
+ std::max(BitWidth - LCPLength - 1, Lower.countr_zero()) + 1));
+}
+
+ConstantRange ConstantRange::cttz(bool ZeroIsPoison) const {
+ if (isEmptySet())
+ return getEmpty();
+
+ APInt Zero = APInt::getZero(getBitWidth());
+
+ if (ZeroIsPoison && contains(Zero)) {
+ // ZeroIsPoison is set, and zero is contained. We discern three cases, in
+ // which a zero can appear:
+ // 1) Lower is zero, handling cases of kind [0, 1), [0, 2), etc.
+ // 2) Upper is zero, wrapped set, handling cases of kind [3, 0], etc.
+ // 3) Zero contained in a wrapped set, e.g., [3, 2), [3, 1), etc.
+
+ if (getLower().isZero()) {
+ if (getUpper() == 1) {
+ // We have in input interval of kind [0, 1). In this case we cannot
+ // really help but return empty-set.
+ return getEmpty();
+ }
+
+ // Compute the resulting range by excluding zero from Lower.
+ return getUnsignedCountTrailingZerosRange(APInt(getBitWidth(), 1),
+ getUpper());
+ } else if (getUpper() == 1) {
+ // Compute the resulting range by excluding zero from Upper.
+ return getUnsignedCountTrailingZerosRange(getLower(), Zero);
+ } else {
+ ConstantRange CR1 = getUnsignedCountTrailingZerosRange(getLower(), Zero);
+ ConstantRange CR2 = getUnsignedCountTrailingZerosRange(
+ APInt(getBitWidth(), 1), getUpper());
+ return CR1.unionWith(CR2);
+ }
+ }
+
+ if (isFullSet())
+ return getNonEmpty(Zero, APInt(getBitWidth(), getBitWidth() + 1));
+ if (!isWrappedSet())
+ return getUnsignedCountTrailingZerosRange(getLower(), getUpper());
+ // The range is wrapped. We decompose it into two ranges, [0, Upper) and
+ // [Lower, 0).
+ // Handle [Lower, 0)
+ ConstantRange CR1 = getUnsignedCountTrailingZerosRange(getLower(), Zero);
+ // Handle [0, Upper)
+ ConstantRange CR2 = getUnsignedCountTrailingZerosRange(Zero, getUpper());
+ return CR1.unionWith(CR2);
+}
+
ConstantRange::OverflowResult ConstantRange::unsignedAddMayOverflow(
const ConstantRange &Other) const {
if (isEmptySet() || Other.isEmptySet())
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/range.ll b/llvm/test/Transforms/CorrelatedValuePropagation/range.ll
index 5c10fdcd2b49217..0be4dfa53a906b6 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/range.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/range.ll
@@ -1016,8 +1016,7 @@ define i1 @cttz_fold(i16 %x) {
; CHECK-NEXT: br i1 [[CMP]], label [[IF:%.*]], label [[ELSE:%.*]]
; CHECK: if:
; CHECK-NEXT: [[CTTZ:%.*]] = call i16 @llvm.cttz.i16(i16 [[X]], i1 true)
-; CHECK-NEXT: [[RES:%.*]] = icmp uge i16 [[CTTZ]], 8
-; CHECK-NEXT: ret i1 [[RES]]
+; CHECK-NEXT: ret i1 false
; CHECK: else:
; CHECK-NEXT: ret i1 false
;
diff --git a/llvm/unittests/IR/ConstantRangeTest.cpp b/llvm/unittests/IR/ConstantRangeTest.cpp
index 1cb358a26062ca5..8cdcd989f24e4f9 100644
--- a/llvm/unittests/IR/ConstantRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantRangeTest.cpp
@@ -2438,6 +2438,20 @@ TEST_F(ConstantRangeTest, Ctlz) {
});
}
+TEST_F(ConstantRangeTest, Cttz) {
+ TestUnaryOpExhaustive(
+ [](const ConstantRange &CR) { return CR.cttz(); },
+ [](const APInt &N) { return APInt(N.getBitWidth(), N.countr_zero()); });
+
+ TestUnaryOpExhaustive(
+ [](const ConstantRange &CR) { return CR.cttz(/*ZeroIsPoison=*/true); },
+ [](const APInt &N) -> std::optional<APInt> {
+ if (N.isZero())
+ return std::nullopt;
+ return APInt(N.getBitWidth(), N.countr_zero());
+ });
+}
+
TEST_F(ConstantRangeTest, castOps) {
ConstantRange A(APInt(16, 66), APInt(16, 128));
ConstantRange FpToI8 = A.castOp(Instruction::FPToSI, 8);
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