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[ValueTracking] Add matchSimpleBinaryIntrinsicRecurrence helper #145964

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Jun 27, 2025
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[ValueTracking] Add matchSimpleBinaryIntrinsicRecurrence helper #145964

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16 changes: 16 additions & 0 deletions llvm/include/llvm/Analysis/ValueTracking.h
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
#include "llvm/IR/FMF.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
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@nikic nikic Jun 27, 2025

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This should be a forward declaration. The include causes a build time regression.

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@antoniofrighetto antoniofrighetto Jun 28, 2025

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Fixed in 69b8e59.

#include "llvm/IR/Intrinsics.h"
#include "llvm/Support/Compiler.h"
#include <cassert>
Expand Down Expand Up @@ -965,6 +966,21 @@ LLVM_ABI bool matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
LLVM_ABI bool matchSimpleRecurrence(const BinaryOperator *I, PHINode *&P,
Value *&Start, Value *&Step);

/// Attempt to match a simple value-accumulating recurrence of the form:
/// %llvm.intrinsic.acc = phi Ty [%Init, %Entry], [%llvm.intrinsic, %backedge]
/// %llvm.intrinsic = call Ty @llvm.intrinsic(%OtherOp, %llvm.intrinsic.acc)
/// OR
/// %llvm.intrinsic.acc = phi Ty [%Init, %Entry], [%llvm.intrinsic, %backedge]
/// %llvm.intrinsic = call Ty @llvm.intrinsic(%llvm.intrinsic.acc, %OtherOp)
///
/// The recurrence relation is of kind:
/// X_0 = %a (initial value),
/// X_i = call @llvm.binary.intrinsic(X_i-1, %b)
/// Where %b is not required to be loop-invariant.
LLVM_ABI bool matchSimpleBinaryIntrinsicRecurrence(const IntrinsicInst *I,
PHINode *&P, Value *&Init,
Value *&OtherOp);

/// Return true if RHS is known to be implied true by LHS. Return false if
/// RHS is known to be implied false by LHS. Otherwise, return std::nullopt if
/// no implication can be made. A & B must be i1 (boolean) values or a vector of
Expand Down
73 changes: 43 additions & 30 deletions llvm/lib/Analysis/ValueTracking.cpp
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Expand Up @@ -9070,46 +9070,43 @@ llvm::canConvertToMinOrMaxIntrinsic(ArrayRef<Value *> VL) {
return {Intrinsic::not_intrinsic, false};
}

bool llvm::matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
Value *&Start, Value *&Step) {
template <typename InstTy>
static bool matchTwoInputRecurrence(const PHINode *PN, InstTy *&Inst,
Value *&Init, Value *&OtherOp) {
// Handle the case of a simple two-predecessor recurrence PHI.
// There's a lot more that could theoretically be done here, but
// this is sufficient to catch some interesting cases.
// TODO: Expand list -- gep, uadd.sat etc.
if (P->getNumIncomingValues() != 2)
if (PN->getNumIncomingValues() != 2)
return false;

for (unsigned i = 0; i != 2; ++i) {
Value *L = P->getIncomingValue(i);
Value *R = P->getIncomingValue(!i);
auto *LU = dyn_cast<BinaryOperator>(L);
if (!LU)
continue;
Value *LL = LU->getOperand(0);
Value *LR = LU->getOperand(1);

// Find a recurrence.
if (LL == P)
L = LR;
else if (LR == P)
L = LL;
else
continue; // Check for recurrence with L and R flipped.

// We have matched a recurrence of the form:
// %iv = [R, %entry], [%iv.next, %backedge]
// %iv.next = binop %iv, L
// OR
// %iv = [R, %entry], [%iv.next, %backedge]
// %iv.next = binop L, %iv
BO = LU;
Start = R;
Step = L;
return true;
for (unsigned I = 0; I != 2; ++I) {
if (auto *Operation = dyn_cast<InstTy>(PN->getIncomingValue(I))) {
Value *LHS = Operation->getOperand(0);
Value *RHS = Operation->getOperand(1);
if (LHS != PN && RHS != PN)
continue;

Inst = Operation;
Init = PN->getIncomingValue(!I);
OtherOp = (LHS == PN) ? RHS : LHS;
return true;
}
}
return false;
}

bool llvm::matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
Value *&Start, Value *&Step) {
// We try to match a recurrence of the form:
// %iv = [Start, %entry], [%iv.next, %backedge]
// %iv.next = binop %iv, Step
// Or:
// %iv = [Start, %entry], [%iv.next, %backedge]
// %iv.next = binop Step, %iv
return matchTwoInputRecurrence(P, BO, Start, Step);
}

bool llvm::matchSimpleRecurrence(const BinaryOperator *I, PHINode *&P,
Value *&Start, Value *&Step) {
BinaryOperator *BO = nullptr;
Expand All @@ -9119,6 +9116,22 @@ bool llvm::matchSimpleRecurrence(const BinaryOperator *I, PHINode *&P,
return P && matchSimpleRecurrence(P, BO, Start, Step) && BO == I;
}

bool llvm::matchSimpleBinaryIntrinsicRecurrence(const IntrinsicInst *I,
PHINode *&P, Value *&Init,
Value *&OtherOp) {
// Binary intrinsics only supported for now.
if (I->arg_size() != 2 || I->getType() != I->getArgOperand(0)->getType() ||
I->getType() != I->getArgOperand(1)->getType())
return false;

IntrinsicInst *II = nullptr;
P = dyn_cast<PHINode>(I->getArgOperand(0));
if (!P)
P = dyn_cast<PHINode>(I->getArgOperand(1));

return P && matchTwoInputRecurrence(P, II, Init, OtherOp) && II == I;
}

/// Return true if "icmp Pred LHS RHS" is always true.
static bool isTruePredicate(CmpInst::Predicate Pred, const Value *LHS,
const Value *RHS) {
Expand Down
52 changes: 52 additions & 0 deletions llvm/unittests/Analysis/ValueTrackingTest.cpp
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Expand Up @@ -1257,6 +1257,58 @@ TEST_F(ValueTrackingTest, computePtrAlignment) {
EXPECT_EQ(getKnownAlignment(A, DL, CxtI3, &AC, &DT), Align(16));
}

TEST_F(ValueTrackingTest, MatchBinaryIntrinsicRecurrenceUMax) {
auto M = parseModule(R"(
define i8 @test(i8 %a, i8 %b) {
entry:
br label %loop
loop:
%iv = phi i8 [ %iv.next, %loop ], [ 0, %entry ]
%umax.acc = phi i8 [ %umax, %loop ], [ %a, %entry ]
%umax = call i8 @llvm.umax.i8(i8 %umax.acc, i8 %b)
%iv.next = add nuw i8 %iv, 1
%cmp = icmp ult i8 %iv.next, 10
br i1 %cmp, label %loop, label %exit
exit:
ret i8 %umax
}
)");

auto *F = M->getFunction("test");
auto *II = &cast<IntrinsicInst>(findInstructionByName(F, "umax"));
auto *UMaxAcc = &cast<PHINode>(findInstructionByName(F, "umax.acc"));
PHINode *PN;
Value *Init, *OtherOp;
EXPECT_TRUE(matchSimpleBinaryIntrinsicRecurrence(II, PN, Init, OtherOp));
EXPECT_EQ(UMaxAcc, PN);
EXPECT_EQ(F->getArg(0), Init);
EXPECT_EQ(F->getArg(1), OtherOp);
}

TEST_F(ValueTrackingTest, MatchBinaryIntrinsicRecurrenceNegativeFSHR) {
auto M = parseModule(R"(
define i8 @test(i8 %a, i8 %b, i8 %c) {
entry:
br label %loop
loop:
%iv = phi i8 [ %iv.next, %loop ], [ 0, %entry ]
%fshr.acc = phi i8 [ %fshr, %loop ], [ %a, %entry ]
%fshr = call i8 @llvm.fshr.i8(i8 %fshr.acc, i8 %b, i8 %c)
%iv.next = add nuw i8 %iv, 1
%cmp = icmp ult i8 %iv.next, 10
br i1 %cmp, label %loop, label %exit
exit:
ret i8 %fshr
}
)");

auto *F = M->getFunction("test");
auto *II = &cast<IntrinsicInst>(findInstructionByName(F, "fshr"));
PHINode *PN;
Value *Init, *OtherOp;
EXPECT_FALSE(matchSimpleBinaryIntrinsicRecurrence(II, PN, Init, OtherOp));
}

TEST_F(ComputeKnownBitsTest, ComputeKnownBits) {
parseAssembly(
"define i32 @test(i32 %a, i32 %b) {\n"
Expand Down
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