[clang] [CIR] Add poison attribute (PR #150760)
Sirui Mu via cfe-commits
cfe-commits at lists.llvm.org
Sat Jul 26 06:11:50 PDT 2025
https://github.com/Lancern created https://github.com/llvm/llvm-project/pull/150760
This patch adds the `#cir.poison` attribute which represents a poison value. This patch also updates various operation folders to let them propagate poison values from their inputs to their outputs.
>From 4a399fa50ef096ee2ad4e46756d79aeaf54b101a Mon Sep 17 00:00:00 2001
From: Sirui Mu <msrlancern at gmail.com>
Date: Sat, 26 Jul 2025 21:07:36 +0800
Subject: [PATCH] [CIR] Add poison attribute
This patch adds the `#cir.poison` attribute which represents a poison value.
This patch also updates various operation folders to let them propagate
poison values from their inputs to their outputs.
---
.../include/clang/CIR/Dialect/IR/CIRAttrs.td | 16 ++++-
clang/include/clang/CIR/MissingFeatures.h | 1 -
clang/lib/CIR/Dialect/IR/CIRDialect.cpp | 30 ++++++--
.../CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp | 6 ++
clang/test/CIR/Lowering/poison.cir | 14 ++++
clang/test/CIR/Transforms/bit.cir | 70 +++++++++++++++++++
clang/test/CIR/Transforms/canonicalize.cir | 20 ++++++
7 files changed, 148 insertions(+), 9 deletions(-)
create mode 100644 clang/test/CIR/Lowering/poison.cir
diff --git a/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td b/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td
index 29d8aea8d08e7..977fe3178c42c 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIRAttrs.td
@@ -127,7 +127,7 @@ def CIR_BoolAttr : CIR_Attr<"Bool", "bool", [TypedAttrInterface]> {
// ZeroAttr
//===----------------------------------------------------------------------===//
-def ZeroAttr : CIR_TypedAttr<"Zero", "zero"> {
+def CIR_ZeroAttr : CIR_TypedAttr<"Zero", "zero"> {
let summary = "Attribute to represent zero initialization";
let description = [{
The ZeroAttr is used to indicate zero initialization on structs.
@@ -138,7 +138,7 @@ def ZeroAttr : CIR_TypedAttr<"Zero", "zero"> {
// UndefAttr
//===----------------------------------------------------------------------===//
-def UndefAttr : CIR_TypedAttr<"Undef", "undef"> {
+def CIR_UndefAttr : CIR_TypedAttr<"Undef", "undef"> {
let summary = "Represent an undef constant";
let description = [{
The UndefAttr represents an undef constant, corresponding to LLVM's notion
@@ -146,6 +146,18 @@ def UndefAttr : CIR_TypedAttr<"Undef", "undef"> {
}];
}
+//===----------------------------------------------------------------------===//
+// PoisonAttr
+//===----------------------------------------------------------------------===//
+
+def CIR_PoisonAttr : CIR_TypedAttr<"Poison", "poison"> {
+ let summary = "Represent a typed poison constant";
+ let description = [{
+ The PoisonAttr represents a typed poison constant, corresponding to LLVM's
+ notion of poison.
+ }];
+}
+
//===----------------------------------------------------------------------===//
// IntegerAttr
//===----------------------------------------------------------------------===//
diff --git a/clang/include/clang/CIR/MissingFeatures.h b/clang/include/clang/CIR/MissingFeatures.h
index d17c85f89d589..e1a5c3d9ca337 100644
--- a/clang/include/clang/CIR/MissingFeatures.h
+++ b/clang/include/clang/CIR/MissingFeatures.h
@@ -287,7 +287,6 @@ struct MissingFeatures {
// Future CIR attributes
static bool optInfoAttr() { return false; }
- static bool poisonAttr() { return false; }
};
} // namespace cir
diff --git a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
index 9c36a43c663cf..0152fcdcc7e01 100644
--- a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
+++ b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
@@ -339,7 +339,7 @@ static LogicalResult checkConstantTypes(mlir::Operation *op, mlir::Type opType,
}
if (mlir::isa<cir::ConstArrayAttr, cir::ConstVectorAttr,
- cir::ConstComplexAttr>(attrType))
+ cir::ConstComplexAttr, cir::PoisonAttr>(attrType))
return success();
assert(isa<TypedAttr>(attrType) && "What else could we be looking at here?");
@@ -629,6 +629,11 @@ static Value tryFoldCastChain(cir::CastOp op) {
}
OpFoldResult cir::CastOp::fold(FoldAdaptor adaptor) {
+ if (mlir::isa_and_present<PoisonAttr>(adaptor.getSrc())) {
+ // Propagate poison value
+ return PoisonAttr::get(getContext(), getType());
+ }
+
if (getSrc().getType() == getType()) {
switch (getKind()) {
case cir::CastKind::integral: {
@@ -1783,6 +1788,11 @@ static bool isBoolNot(cir::UnaryOp op) {
//
// and the argument of the first one (%0) will be used instead.
OpFoldResult cir::UnaryOp::fold(FoldAdaptor adaptor) {
+ if (auto poison = mlir::dyn_cast_if_present<PoisonAttr>(adaptor.getInput())) {
+ // Propagate poison values
+ return poison;
+ }
+
if (isBoolNot(*this))
if (auto previous = dyn_cast_or_null<UnaryOp>(getInput().getDefiningOp()))
if (isBoolNot(previous))
@@ -2239,16 +2249,18 @@ static OpFoldResult
foldUnaryBitOp(mlir::Attribute inputAttr,
llvm::function_ref<llvm::APInt(const llvm::APInt &)> func,
bool poisonZero = false) {
+ if (mlir::isa_and_present<PoisonAttr>(inputAttr)) {
+ // Propagate poison value
+ return inputAttr;
+ }
+
auto input = mlir::dyn_cast_if_present<IntAttr>(inputAttr);
if (!input)
return nullptr;
llvm::APInt inputValue = input.getValue();
- if (poisonZero && inputValue.isZero()) {
- // TODO(cir): maybe we should return a poison value here?
- assert(!MissingFeatures::poisonAttr());
- return nullptr;
- }
+ if (poisonZero && inputValue.isZero())
+ return PoisonAttr::get(input.getType());
llvm::APInt resultValue = func(inputValue);
return IntAttr::get(input.getType(), resultValue);
@@ -2307,6 +2319,12 @@ OpFoldResult ByteSwapOp::fold(FoldAdaptor adaptor) {
}
OpFoldResult RotateOp::fold(FoldAdaptor adaptor) {
+ if (mlir::isa_and_present<PoisonAttr>(adaptor.getInput()) ||
+ mlir::isa_and_present<PoisonAttr>(adaptor.getAmount())) {
+ // Propagate poison values
+ return PoisonAttr::get(getType());
+ }
+
auto input = mlir::dyn_cast_if_present<IntAttr>(adaptor.getInput());
auto amount = mlir::dyn_cast_if_present<IntAttr>(adaptor.getAmount());
if (!input && !amount)
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index 3cd7de0a56bc3..c27b8899ba596 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -1027,6 +1027,12 @@ mlir::LogicalResult CIRToLLVMConstantOpLowering::matchAndRewrite(
mlir::ConversionPatternRewriter &rewriter) const {
mlir::Attribute attr = op.getValue();
+ if (mlir::isa<cir::PoisonAttr>(attr)) {
+ rewriter.replaceOpWithNewOp<mlir::LLVM::PoisonOp>(
+ op, getTypeConverter()->convertType(op.getType()));
+ return mlir::success();
+ }
+
if (mlir::isa<mlir::IntegerType>(op.getType())) {
// Verified cir.const operations cannot actually be of these types, but the
// lowering pass may generate temporary cir.const operations with these
diff --git a/clang/test/CIR/Lowering/poison.cir b/clang/test/CIR/Lowering/poison.cir
new file mode 100644
index 0000000000000..6f8b7927e3f8f
--- /dev/null
+++ b/clang/test/CIR/Lowering/poison.cir
@@ -0,0 +1,14 @@
+// RUN: cir-translate -cir-to-llvmir --disable-cc-lowering -o %t.ll %s
+// RUN: FileCheck -check-prefix=LLVM --input-file=%t.ll %s
+
+!s32i = !cir.int<s, 32>
+
+module {
+ cir.func @lower_poison() -> !s32i {
+ %0 = cir.const #cir.poison : !s32i
+ cir.return %0 : !s32i
+ }
+ // LLVM-LABEL: @lower_poison
+ // LLVM-NEXT: ret i32 poison
+ // LLVM-NEXT: }
+}
diff --git a/clang/test/CIR/Transforms/bit.cir b/clang/test/CIR/Transforms/bit.cir
index c85b05de4d9ea..fc27adbc9bb88 100644
--- a/clang/test/CIR/Transforms/bit.cir
+++ b/clang/test/CIR/Transforms/bit.cir
@@ -25,6 +25,26 @@ module {
// CHECK-NEXT: cir.return %[[R]] : !u32i
// CHECK-NEXT: }
+ cir.func @fold_clz_zero_poison() -> !u32i {
+ %0 = cir.const #cir.int<0> : !u32i
+ %1 = cir.clz %0 poison_zero : !u32i
+ cir.return %1 : !u32i
+ }
+ // CHECK-LABEL: @fold_clz_zero_poison
+ // CHECK-NEXT: %[[R:.+]] = cir.const #cir.poison : !u32i
+ // CHECK-NEXT: cir.return %[[R]] : !u32i
+ // CHECK-NEXT: }
+
+ cir.func @fold_clz_zero_no_poison() -> !u32i {
+ %0 = cir.const #cir.int<0> : !u32i
+ %1 = cir.clz %0 : !u32i
+ cir.return %1 : !u32i
+ }
+ // CHECK-LABEL: @fold_clz_zero_no_poison
+ // CHECK-NEXT: %[[R:.+]] = cir.const #cir.int<32> : !u32i
+ // CHECK-NEXT: cir.return %[[R]] : !u32i
+ // CHECK-NEXT: }
+
cir.func @fold_ctz() -> !u32i {
%0 = cir.const #cir.int<2> : !u32i
%1 = cir.ctz %0 : !u32i
@@ -35,6 +55,26 @@ module {
// CHECK-NEXT: cir.return %[[R]] : !u32i
// CHECK-NEXT: }
+ cir.func @fold_ctz_zero_poison() -> !u32i {
+ %0 = cir.const #cir.int<0> : !u32i
+ %1 = cir.ctz %0 poison_zero : !u32i
+ cir.return %1 : !u32i
+ }
+ // CHECK-LABEL: @fold_ctz_zero_poison
+ // CHECK-NEXT: %[[R:.+]] = cir.const #cir.poison : !u32i
+ // CHECK-NEXT: cir.return %[[R]] : !u32i
+ // CHECK-NEXT: }
+
+ cir.func @fold_ctz_zero_no_poison() -> !u32i {
+ %0 = cir.const #cir.int<0> : !u32i
+ %1 = cir.ctz %0 : !u32i
+ cir.return %1 : !u32i
+ }
+ // CHECK-LABEL: @fold_ctz_zero_no_poison
+ // CHECK-NEXT: %[[R:.+]] = cir.const #cir.int<32> : !u32i
+ // CHECK-NEXT: cir.return %[[R]] : !u32i
+ // CHECK-NEXT: }
+
cir.func @fold_parity() -> !u32i {
// 0xdeadbeef is 0b1101_1110_1010_1101_1011_1110_1110_1111
// 0xdeadbeef contains 24 ones
@@ -82,6 +122,16 @@ module {
// CHECK-NEXT: cir.return %[[R]] : !u32i
// CHECK-NEXT: }
+ cir.func @fold_input_poison() -> !s32i {
+ %0 = cir.const #cir.poison : !s32i
+ %1 = cir.clrsb %0 : !s32i
+ cir.return %1 : !s32i
+ }
+ // CHECK-LABEL: @fold_input_poison
+ // CHECK-NEXT: %[[P:.+]] = cir.const #cir.poison : !s32i
+ // CHECK-NEXT: cir.return %[[P]] : !s32i
+ // CHECK-NEXT: }
+
cir.func @fold_rotate_input_all_zeros(%arg0 : !u32i) -> !u32i {
%0 = cir.const #cir.int<0> : !u32i
%1 = cir.rotate left %0, %arg0 : !u32i
@@ -138,4 +188,24 @@ module {
// CHECK-NEXT: %[[R:.+]] = cir.const #cir.int<4024348094> : !u32i
// CHECK-NEXT: cir.return %[[R]] : !u32i
// CHECK-NEXT: }
+
+ cir.func @fold_rotate_input_poison(%arg0 : !u32i) -> !u32i {
+ %0 = cir.const #cir.poison : !u32i
+ %1 = cir.rotate left %0, %arg0 : !u32i
+ cir.return %1 : !u32i
+ }
+ // CHECK-LABEL: @fold_rotate_input_poison
+ // CHECK-NEXT: %[[P:.+]] = cir.const #cir.poison : !u32i
+ // CHECK-NEXT: cir.return %[[P]] : !u32i
+ // CHECK-NEXT: }
+
+ cir.func @fold_rotate_amount_poison(%arg0 : !u32i) -> !u32i {
+ %0 = cir.const #cir.poison : !u32i
+ %1 = cir.rotate left %arg0, %0 : !u32i
+ cir.return %1 : !u32i
+ }
+ // CHECK-LABEL: @fold_rotate_amount_poison
+ // CHECK-NEXT: %[[P:.+]] = cir.const #cir.poison : !u32i
+ // CHECK-NEXT: cir.return %[[P]] : !u32i
+ // CHECK-NEXT: }
}
diff --git a/clang/test/CIR/Transforms/canonicalize.cir b/clang/test/CIR/Transforms/canonicalize.cir
index 7ba163eb30bb1..5daff119a626f 100644
--- a/clang/test/CIR/Transforms/canonicalize.cir
+++ b/clang/test/CIR/Transforms/canonicalize.cir
@@ -39,6 +39,16 @@ module {
// CHECK: cir.func{{.*}} @unary_not(%arg0: !cir.bool) -> !cir.bool
// CHECK-NEXT: cir.return %arg0 : !cir.bool
+ cir.func @unary_poison() -> !s32i {
+ %0 = cir.const #cir.poison : !s32i
+ %1 = cir.unary(inc, %0) : !s32i, !s32i
+ cir.return %1 : !s32i
+ }
+ // CHECK: @unary_poison
+ // CHECK-NEXT: %[[P:.+]] = cir.const #cir.poison : !s32i
+ // CHECK-NEXT: cir.return %[[P]] : !s32i
+ // CHECK-NEXT: }
+
cir.func @cast1(%arg0: !cir.bool) -> !cir.bool {
%0 = cir.cast(bool_to_int, %arg0 : !cir.bool), !s32i
%1 = cir.cast(int_to_bool, %0 : !s32i), !cir.bool
@@ -70,4 +80,14 @@ module {
// CHECK-NEXT: %[[CAST3:.*]] = cir.cast(integral, %[[CAST2]] : !s32i), !s64i
// CHECK-NEXT: cir.return %[[CAST3]] : !s64i
+ cir.func @cast_poison() -> !s64i {
+ %0 = cir.const #cir.poison : !s32i
+ %1 = cir.cast(integral, %0 : !s32i), !s64i
+ cir.return %1 : !s64i
+ }
+ // CHECK: @cast_poison
+ // CHECK-NEXT: %[[P:.+]] = cir.const #cir.poison : !s64i
+ // CHECK-NEXT: cir.return %[[P]] : !s64i
+ // CHECK-NEXT: }
+
}
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