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[CIR][ThroughMLIR] Lower uncanonicalized fors to whiles #1644

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Merged
merged 1 commit into from
May 27, 2025
Merged

[CIR][ThroughMLIR] Lower uncanonicalized fors to whiles #1644

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84 changes: 57 additions & 27 deletions clang/lib/CIR/Lowering/ThroughMLIR/LowerCIRLoopToSCF.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,20 +13,15 @@
#include "mlir/Dialect/Arith/IR/Arith.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
#include "mlir/Dialect/SCF/IR/SCF.h"
#include "mlir/Dialect/SCF/Transforms/Passes.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinDialect.h"
#include "mlir/IR/BuiltinTypes.h"
#include "mlir/IR/Location.h"
#include "mlir/IR/ValueRange.h"
#include "mlir/Pass/Pass.h"
#include "mlir/Pass/PassManager.h"
#include "mlir/Support/LogicalResult.h"
#include "mlir/Transforms/DialectConversion.h"
#include "clang/CIR/Dialect/IR/CIRDialect.h"
#include "clang/CIR/Dialect/IR/CIRTypes.h"
#include "clang/CIR/LowerToMLIR.h"
#include "clang/CIR/Passes.h"
#include "llvm/ADT/TypeSwitch.h"

using namespace cir;
Expand All @@ -52,6 +47,7 @@ class SCFLoop {

mlir::Value plusConstant(mlir::Value v, mlir::Location loc, int addend);
void transferToSCFForOp();
void transformToSCFWhileOp();

private:
cir::ForOp forOp;
Expand Down Expand Up @@ -209,21 +205,21 @@ cir::CmpOp SCFLoop::findCmpOp() {
}
}
if (!cmpOp)
llvm_unreachable("Can't find loop CmpOp");
return nullptr;

auto type = cmpOp.getLhs().getType();
if (!mlir::isa<cir::IntType>(type))
llvm_unreachable("Non-integer type IV is not supported");
return nullptr;

auto *lhsDefOp = cmpOp.getLhs().getDefiningOp();
if (!lhsDefOp)
llvm_unreachable("Can't find IV load");
return nullptr;
if (!isIVLoad(lhsDefOp, ivAddr))
llvm_unreachable("cmpOp LHS is not IV");
return nullptr;

if (cmpOp.getKind() != cir::CmpOpKind::le &&
cmpOp.getKind() != cir::CmpOpKind::lt)
llvm_unreachable("Not support lowering other than le or lt comparison");
return nullptr;

return cmpOp;
}
Expand Down Expand Up @@ -253,30 +249,40 @@ mlir::Value SCFLoop::findIVInitValue() {

void SCFLoop::analysis() {
canonical = mlir::succeeded(findStepAndIV());
if (!canonical) {
mlir::emitError(forOp.getLoc(),
"cannot handle non-constant step for induction variable");
if (!canonical)
return;
}

cmpOp = findCmpOp();
auto IVInit = findIVInitValue();
if (!cmpOp) {
canonical = false;
return;
}

auto ivInit = findIVInitValue();
if (!ivInit) {
canonical = false;
return;
}

// The loop end value should be hoisted out of loop by -cir-mlir-scf-prepare.
// So we could get the value by getRemappedValue.
auto IVEndBound = rewriter->getRemappedValue(cmpOp.getRhs());
// If the loop end bound is not loop invariant and can't be hoisted.
// The following assertion will be triggerred.
assert(IVEndBound && "can't find IV end boundary");
auto ivEndBound = rewriter->getRemappedValue(cmpOp.getRhs());
// If the loop end bound is not loop invariant and can't be hoisted,
// then this is not a canonical loop.
if (!ivEndBound) {
canonical = false;
return;
}

if (step > 0) {
lowerBound = IVInit;
lowerBound = ivInit;
if (cmpOp.getKind() == cir::CmpOpKind::lt)
upperBound = IVEndBound;
upperBound = ivEndBound;
else if (cmpOp.getKind() == cir::CmpOpKind::le)
upperBound = plusConstant(IVEndBound, cmpOp.getLoc(), 1);
upperBound = plusConstant(ivEndBound, cmpOp.getLoc(), 1);
}
assert(lowerBound && "can't find loop lower bound");
assert(upperBound && "can't find loop upper bound");
if (!lowerBound || !upperBound)
canonical = false;
}

void SCFLoop::transferToSCFForOp() {
Expand Down Expand Up @@ -309,6 +315,28 @@ void SCFLoop::transferToSCFForOp() {
});
}

void SCFLoop::transformToSCFWhileOp() {
auto scfWhileOp = rewriter->create<mlir::scf::WhileOp>(
forOp->getLoc(), forOp->getResultTypes(), mlir::ValueRange());
rewriter->createBlock(&scfWhileOp.getBefore());
rewriter->createBlock(&scfWhileOp.getAfter());

rewriter->inlineBlockBefore(&forOp.getCond().front(),
scfWhileOp.getBeforeBody(),
scfWhileOp.getBeforeBody()->end());
rewriter->inlineBlockBefore(&forOp.getBody().front(),
scfWhileOp.getAfterBody(),
scfWhileOp.getAfterBody()->end());
// There will be a yield after the `for` body.
// We should delete it.
auto yield = mlir::cast<YieldOp>(scfWhileOp.getAfterBody()->back());
rewriter->eraseOp(yield);

rewriter->inlineBlockBefore(&forOp.getStep().front(),
scfWhileOp.getAfterBody(),
scfWhileOp.getAfterBody()->end());
}

void SCFWhileLoop::transferToSCFWhileOp() {
auto scfWhileOp = rewriter->create<mlir::scf::WhileOp>(
whileOp->getLoc(), whileOp->getResultTypes(), adaptor.getOperands());
Expand Down Expand Up @@ -352,9 +380,11 @@ class CIRForOpLowering : public mlir::OpConversionPattern<cir::ForOp> {
mlir::ConversionPatternRewriter &rewriter) const override {
SCFLoop loop(op, &rewriter);
loop.analysis();
if (!loop.isCanonical())
return mlir::emitError(op.getLoc(),
"cannot handle non-canonicalized loop");
if (!loop.isCanonical()) {
loop.transformToSCFWhileOp();
rewriter.eraseOp(op);
return mlir::success();
}

loop.transferToSCFForOp();
rewriter.eraseOp(op);
Expand Down
23 changes: 19 additions & 4 deletions clang/test/CIR/Lowering/ThroughMLIR/for-reject-1.cpp
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Original file line number Diff line number Diff line change
@@ -1,9 +1,24 @@
// RUN: not %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -fno-clangir-direct-lowering -emit-mlir=core %s -o - 2>&1 | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -fno-clangir-direct-lowering -emit-mlir=core %s -o %t.mlir
// RUN: FileCheck --input-file=%t.mlir %s

void f();
void f() {}

void reject() {
for (int i = 0; i < 100; i++, f());
// CHECK: cannot handle non-constant step for induction variable
// CHECK: cannot handle non-canonicalized loop
// CHECK: %[[ALLOCA:.+]] = memref.alloca
// CHECK: %[[ZERO:.+]] = arith.constant 0
// CHECK: memref.store %[[ZERO]], %[[ALLOCA]]
// CHECK: %[[HUNDRED:.+]] = arith.constant 100
// CHECK: scf.while : () -> () {
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Since these are not rejected anymore, just remove these files. Create a new one that tests the lowering for the snippet here + the one from the other test.

// CHECK: %[[TMP:.+]] = memref.load %[[ALLOCA]]
// CHECK: %[[TMP1:.+]] = arith.cmpi slt, %0, %[[HUNDRED]]
// CHECK: scf.condition(%[[TMP1]])
// CHECK: } do {
// CHECK: %[[TMP2:.+]] = memref.load %[[ALLOCA]]
// CHECK: %[[ONE:.+]] = arith.constant 1
// CHECK: %[[TMP3:.+]] = arith.addi %[[TMP2]], %[[ONE]]
// CHECK: memref.store %[[TMP3]], %[[ALLOCA]]
// CHECK: func.call @_Z1fv()
// CHECK: scf.yield
// CHECK: }
}
24 changes: 21 additions & 3 deletions clang/test/CIR/Lowering/ThroughMLIR/for-reject-2.cpp
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Original file line number Diff line number Diff line change
@@ -1,7 +1,25 @@
// RUN: not %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -fno-clangir-direct-lowering -emit-mlir=core %s -o - 2>&1 | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -fno-clangir-direct-lowering -emit-mlir=core %s -o %t.mlir
// RUN: FileCheck --input-file=%t.mlir %s

void reject() {
for (int i = 0; i < 100; i++, i++);
// CHECK: cannot handle non-constant step for induction variable
// CHECK: cannot handle non-canonicalized loop
// CHECK: %[[ALLOCA:.+]] = memref.alloca
// CHECK: %[[ZERO:.+]] = arith.constant 0
// CHECK: memref.store %[[ZERO]], %[[ALLOCA]]
// CHECK: %[[HUNDRED:.+]] = arith.constant 100
// CHECK: scf.while : () -> () {
// CHECK: %[[TMP:.+]] = memref.load %[[ALLOCA]]
// CHECK: %[[TMP2:.+]] = arith.cmpi slt, %[[TMP]], %[[HUNDRED]]
// CHECK: scf.condition(%[[TMP2]])
// CHECK: } do {
// CHECK: %[[TMP3:.+]] = memref.load %[[ALLOCA]]
// CHECK: %[[ONE:.+]] = arith.constant 1
// CHECK: %[[ADD:.+]] = arith.addi %[[TMP3]], %[[ONE]]
// CHECK: memref.store %[[ADD]], %[[ALLOCA]]
// CHECK: %[[LOAD:.+]] = memref.load %[[ALLOCA]]
// CHECK: %[[ONE2:.+]] = arith.constant 1
// CHECK: %[[ADD2:.+]] = arith.addi %[[LOAD]], %[[ONE2]]
// CHECK: memref.store %[[ADD2]], %[[ALLOCA]]
// CHECK: scf.yield
// CHECK: }
}
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