[llvm] [ValueTracking] Move the `isSignBitCheck` helper into ValueTracking. NFC. (PR #81704)
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Tue Feb 13 21:03:14 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
This patch moves the `isSignBitCheck` helper into ValueTracking to reuse the logic in ValueTracking/InstSimplify.
Addresses the comment https://github.com/llvm/llvm-project/pull/80740#discussion_r1488440050.
---
Full diff: https://github.com/llvm/llvm-project/pull/81704.diff
6 Files Affected:
- (modified) llvm/include/llvm/Analysis/ValueTracking.h (+6)
- (modified) llvm/include/llvm/Transforms/InstCombine/InstCombiner.h (-39)
- (modified) llvm/lib/Analysis/InstructionSimplify.cpp (+7-8)
- (modified) llvm/lib/Analysis/ValueTracking.cpp (+39)
- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+1-1)
- (modified) llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp (+3-4)
``````````diff
diff --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
index 06f94f58ae5eff..f0d0ee554f12b2 100644
--- a/llvm/include/llvm/Analysis/ValueTracking.h
+++ b/llvm/include/llvm/Analysis/ValueTracking.h
@@ -197,6 +197,12 @@ unsigned ComputeMaxSignificantBits(const Value *Op, const DataLayout &DL,
Intrinsic::ID getIntrinsicForCallSite(const CallBase &CB,
const TargetLibraryInfo *TLI);
+/// Given an exploded icmp instruction, return true if the comparison only
+/// checks the sign bit. If it only checks the sign bit, set TrueIfSigned if
+/// the result of the comparison is true when the input value is signed.
+bool isSignBitCheck(ICmpInst::Predicate Pred, const APInt &RHS,
+ bool &TrueIfSigned);
+
/// Returns a pair of values, which if passed to llvm.is.fpclass, returns the
/// same result as an fcmp with the given operands.
///
diff --git a/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h b/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
index 950cc8c9d1658a..93090431cbb69f 100644
--- a/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
+++ b/llvm/include/llvm/Transforms/InstCombine/InstCombiner.h
@@ -170,45 +170,6 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner {
}
}
- /// Given an exploded icmp instruction, return true if the comparison only
- /// checks the sign bit. If it only checks the sign bit, set TrueIfSigned if
- /// the result of the comparison is true when the input value is signed.
- static bool isSignBitCheck(ICmpInst::Predicate Pred, const APInt &RHS,
- bool &TrueIfSigned) {
- switch (Pred) {
- case ICmpInst::ICMP_SLT: // True if LHS s< 0
- TrueIfSigned = true;
- return RHS.isZero();
- case ICmpInst::ICMP_SLE: // True if LHS s<= -1
- TrueIfSigned = true;
- return RHS.isAllOnes();
- case ICmpInst::ICMP_SGT: // True if LHS s> -1
- TrueIfSigned = false;
- return RHS.isAllOnes();
- case ICmpInst::ICMP_SGE: // True if LHS s>= 0
- TrueIfSigned = false;
- return RHS.isZero();
- case ICmpInst::ICMP_UGT:
- // True if LHS u> RHS and RHS == sign-bit-mask - 1
- TrueIfSigned = true;
- return RHS.isMaxSignedValue();
- case ICmpInst::ICMP_UGE:
- // True if LHS u>= RHS and RHS == sign-bit-mask (2^7, 2^15, 2^31, etc)
- TrueIfSigned = true;
- return RHS.isMinSignedValue();
- case ICmpInst::ICMP_ULT:
- // True if LHS u< RHS and RHS == sign-bit-mask (2^7, 2^15, 2^31, etc)
- TrueIfSigned = false;
- return RHS.isMinSignedValue();
- case ICmpInst::ICMP_ULE:
- // True if LHS u<= RHS and RHS == sign-bit-mask - 1
- TrueIfSigned = false;
- return RHS.isMaxSignedValue();
- default:
- return false;
- }
- }
-
/// Add one to a Constant
static Constant *AddOne(Constant *C) {
return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1));
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 51e258d69e9e2e..8c2455efc592be 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3031,21 +3031,20 @@ static Value *simplifyICmpWithConstant(CmpInst::Predicate Pred, Value *LHS,
Type *ITy = getCompareTy(RHS); // The return type.
Value *X;
+ const APInt *C;
+ if (!match(RHS, m_APIntAllowUndef(C)))
+ return nullptr;
+
// Sign-bit checks can be optimized to true/false after unsigned
// floating-point casts:
// icmp slt (bitcast (uitofp X)), 0 --> false
// icmp sgt (bitcast (uitofp X)), -1 --> true
if (match(LHS, m_ElementWiseBitCast(m_UIToFP(m_Value(X))))) {
- if (Pred == ICmpInst::ICMP_SLT && match(RHS, m_Zero()))
- return ConstantInt::getFalse(ITy);
- if (Pred == ICmpInst::ICMP_SGT && match(RHS, m_AllOnes()))
- return ConstantInt::getTrue(ITy);
+ bool TrueIfSigned;
+ if (isSignBitCheck(Pred, *C, TrueIfSigned))
+ return ConstantInt::getBool(ITy, !TrueIfSigned);
}
- const APInt *C;
- if (!match(RHS, m_APIntAllowUndef(C)))
- return nullptr;
-
// Rule out tautological comparisons (eg., ult 0 or uge 0).
ConstantRange RHS_CR = ConstantRange::makeExactICmpRegion(Pred, *C);
if (RHS_CR.isEmptySet())
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 92c9162a1f8f0f..6c42facea3b2b3 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3810,6 +3810,45 @@ void KnownFPClass::propagateCanonicalizingSrc(const KnownFPClass &Src,
propagateNaN(Src, /*PreserveSign=*/true);
}
+/// Given an exploded icmp instruction, return true if the comparison only
+/// checks the sign bit. If it only checks the sign bit, set TrueIfSigned if
+/// the result of the comparison is true when the input value is signed.
+bool llvm::isSignBitCheck(ICmpInst::Predicate Pred, const APInt &RHS,
+ bool &TrueIfSigned) {
+ switch (Pred) {
+ case ICmpInst::ICMP_SLT: // True if LHS s< 0
+ TrueIfSigned = true;
+ return RHS.isZero();
+ case ICmpInst::ICMP_SLE: // True if LHS s<= -1
+ TrueIfSigned = true;
+ return RHS.isAllOnes();
+ case ICmpInst::ICMP_SGT: // True if LHS s> -1
+ TrueIfSigned = false;
+ return RHS.isAllOnes();
+ case ICmpInst::ICMP_SGE: // True if LHS s>= 0
+ TrueIfSigned = false;
+ return RHS.isZero();
+ case ICmpInst::ICMP_UGT:
+ // True if LHS u> RHS and RHS == sign-bit-mask - 1
+ TrueIfSigned = true;
+ return RHS.isMaxSignedValue();
+ case ICmpInst::ICMP_UGE:
+ // True if LHS u>= RHS and RHS == sign-bit-mask (2^7, 2^15, 2^31, etc)
+ TrueIfSigned = true;
+ return RHS.isMinSignedValue();
+ case ICmpInst::ICMP_ULT:
+ // True if LHS u< RHS and RHS == sign-bit-mask (2^7, 2^15, 2^31, etc)
+ TrueIfSigned = false;
+ return RHS.isMinSignedValue();
+ case ICmpInst::ICMP_ULE:
+ // True if LHS u<= RHS and RHS == sign-bit-mask - 1
+ TrueIfSigned = false;
+ return RHS.isMaxSignedValue();
+ default:
+ return false;
+ }
+}
+
/// Returns a pair of values, which if passed to llvm.is.fpclass, returns the
/// same result as an fcmp with the given operands.
std::pair<Value *, FPClassTest> llvm::fcmpToClassTest(FCmpInst::Predicate Pred,
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 280c4d77b6dfca..1104ea84e4bc70 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6021,7 +6021,7 @@ static APInt getDemandedBitsLHSMask(ICmpInst &I, unsigned BitWidth) {
// If this is a normal comparison, it demands all bits. If it is a sign bit
// comparison, it only demands the sign bit.
bool UnusedBit;
- if (InstCombiner::isSignBitCheck(I.getPredicate(), *RHS, UnusedBit))
+ if (isSignBitCheck(I.getPredicate(), *RHS, UnusedBit))
return APInt::getSignMask(BitWidth);
switch (I.getPredicate()) {
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 527037881edb19..71fa9b9ba41ebb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2381,8 +2381,7 @@ static Instruction *foldSelectToCopysign(SelectInst &Sel,
ICmpInst::Predicate Pred;
if (!match(Cond, m_OneUse(m_ICmp(Pred, m_ElementWiseBitCast(m_Value(X)),
m_APInt(C)))) ||
- !InstCombiner::isSignBitCheck(Pred, *C, IsTrueIfSignSet) ||
- X->getType() != SelType)
+ !isSignBitCheck(Pred, *C, IsTrueIfSignSet) || X->getType() != SelType)
return nullptr;
// If needed, negate the value that will be the sign argument of the copysign:
@@ -2581,7 +2580,7 @@ static Instruction *foldSelectWithSRem(SelectInst &SI, InstCombinerImpl &IC,
bool TrueIfSigned = false;
if (!(match(CondVal, m_ICmp(Pred, m_Value(RemRes), m_APInt(C))) &&
- IC.isSignBitCheck(Pred, *C, TrueIfSigned)))
+ isSignBitCheck(Pred, *C, TrueIfSigned)))
return nullptr;
// If the sign bit is not set, we have a SGE/SGT comparison, and the operands
@@ -2781,7 +2780,7 @@ static Instruction *foldSelectWithFCmpToFabs(SelectInst &SI,
bool TrueIfSigned;
if (!match(CondVal,
m_ICmp(Pred, m_ElementWiseBitCast(m_Specific(X)), m_APInt(C))) ||
- !IC.isSignBitCheck(Pred, *C, TrueIfSigned))
+ !isSignBitCheck(Pred, *C, TrueIfSigned))
continue;
if (!match(TrueVal, m_FNeg(m_Specific(X))))
return nullptr;
``````````
</details>
https://github.com/llvm/llvm-project/pull/81704
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