[clang] [CIR] Lowering __builtin_stdc_* calls (PR #214931)
Kunal Dubey via cfe-commits
cfe-commits at lists.llvm.org
Mon Aug 10 05:58:02 PDT 2026
https://github.com/xakep8 updated https://github.com/llvm/llvm-project/pull/214931
>From 92b788bc02d91996ff986b3f3f54927bcf90ca64 Mon Sep 17 00:00:00 2001
From: Kunal Dubey <xakep8 at protonmail.com>
Date: Sat, 8 Aug 2026 10:19:23 +0530
Subject: [PATCH 1/4] [CIR] Lowering __builtin_stdc_trailing_zeros
Added CIRGen support for __builtin_stdc_trailing_zeros by lowering it to
cir.ctz with zero behaviour defined, matching with the C23 stdbit
semantics.
Added CodeGen test for the same.
---
clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp | 7 +++++++
clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c | 10 ++++++++++
2 files changed, 17 insertions(+)
create mode 100644 clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index 1efe2b81d5cae..2eb9d6c3bb661 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -1247,6 +1247,13 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
getTarget().isCLZForZeroUndef());
case Builtin::BI__builtin_ctzg:
return emitBuiltinBitOpWithFallback<cir::BitCtzOp>(*this, e);
+ case Builtin::BIstdc_trailing_zeros_uc:
+ case Builtin::BIstdc_trailing_zeros_us:
+ case Builtin::BIstdc_trailiing_zeros_ui:
+ case Builtin::BIstdc_trailing_zeros_ul:
+ case Builtin::BIstdc_trailing_zeros_ull:
+ case Builtin::BI__builtin_stdc_trailing_zeros:
+ return emitBuiltinBitOp<cir::BitCtzOp>(*this, e, /*poisonZero=*/false);
case Builtin::BI__builtin_clzs:
case Builtin::BI__builtin_clz:
diff --git a/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
new file mode 100644
index 0000000000000..6d285c259a96f
--- /dev/null
+++ b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o - | FileCheck %s
+
+void test_stdc_trailing_zeros(unsigned long long x) {
+ int cnt = __builtin_stdc_trailing_zeros(x);
+ (void)cnt;
+}
+
+// CHECK-LABEL: test_stdc_trailing_zeros
+// CHECK: cir.ctz
+// CHECK-NOT: poison_zero
>From 06447c7643d7cb9a65d533d440b98411b6d02299 Mon Sep 17 00:00:00 2001
From: Kunal Dubey <xakep8 at protonmail.com>
Date: Sat, 8 Aug 2026 11:31:41 +0530
Subject: [PATCH 2/4] [CIR] Lowering __builtin_stdc_leading_zeros
Added CIRGen support for __builtin_stdc_leading_zeros by lowering to
cir.clz with zero behaviour defined, matching C23 stdbit semantics.
Added CodeGen test for the same.
---
clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp | 8 ++++++++
.../CIR/CodeGenBuiltins/builtin-stdc-bit.c | 19 +++++++++++++++++++
2 files changed, 27 insertions(+)
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index 2eb9d6c3bb661..bbc82f33571d4 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -1255,6 +1255,14 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
case Builtin::BI__builtin_stdc_trailing_zeros:
return emitBuiltinBitOp<cir::BitCtzOp>(*this, e, /*poisonZero=*/false);
+ case Builtin::BIstdc_leading_zeros_uc:
+ case Builtin::BIstdc_leading_zeros_us:
+ case Builtin::BIstdc_leading_zeros_ui:
+ case Builtin::BIstdc_leading_zeros_ul:
+ case Builtin::BIstdc_leading_zeros_ull:
+ case Builtin::BI__builtin_stdc_leading_zeros:
+ return emitBuiltinBitOp<cir::BitClzOp>(*this, e, /*poisonZero=*/false);
+
case Builtin::BI__builtin_clzs:
case Builtin::BI__builtin_clz:
case Builtin::BI__builtin_clzl:
diff --git a/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
index 6d285c259a96f..1f127821673d2 100644
--- a/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
+++ b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
@@ -8,3 +8,22 @@ void test_stdc_trailing_zeros(unsigned long long x) {
// CHECK-LABEL: test_stdc_trailing_zeros
// CHECK: cir.ctz
// CHECK-NOT: poison_zero
+// CHECK: cir.return
+
+void test_stdc_leading_zeros(unsigned x) {
+ return __builtin_stdc_trailing_zeros(x);
+}
+
+// CHECK-LABEL: test_stdc_leading_zeros
+// CHECK: cir.clz
+// CHECK-NOT: poison_zero
+// CHECK: cir.return
+
+void test_stdc_leading_zeros_ui(unsigned x) {
+ return stdc_leading_zeros_ui(x);
+}
+
+// CHECK-LABEL: test_stdc_leading_zeros_ui
+// CHECK: cir.clz
+// CHECK-NOT: poison_zero
+// CHECK: cir.return
>From 7a91d44a11c0774d2c8f149eb66ee3593add00eb Mon Sep 17 00:00:00 2001
From: Kunal Dubey <xakep8 at protonmail.com>
Date: Sun, 9 Aug 2026 16:33:16 +0530
Subject: [PATCH 3/4] [CIR] Lowering __builtin_stdc_count_ones
Added CIRGen support for lowering of __builtin_stdc_count_ones by
lowering to cir.popcount, matching with the C23 stdbit semantics.
Added test for the same.
---
clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp | 10 ++++++++-
.../CIR/CodeGenBuiltins/builtin-stdc-bit.c | 22 ++++++++++++++++---
2 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index bbc82f33571d4..d27ace31cef78 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -1249,7 +1249,7 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
return emitBuiltinBitOpWithFallback<cir::BitCtzOp>(*this, e);
case Builtin::BIstdc_trailing_zeros_uc:
case Builtin::BIstdc_trailing_zeros_us:
- case Builtin::BIstdc_trailiing_zeros_ui:
+ case Builtin::BIstdc_trailing_zeros_ui:
case Builtin::BIstdc_trailing_zeros_ul:
case Builtin::BIstdc_trailing_zeros_ull:
case Builtin::BI__builtin_stdc_trailing_zeros:
@@ -1263,6 +1263,14 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
case Builtin::BI__builtin_stdc_leading_zeros:
return emitBuiltinBitOp<cir::BitClzOp>(*this, e, /*poisonZero=*/false);
+ case Builtin::BIstdc_count_ones_uc:
+ case Builtin::BIstdc_count_ones_us:
+ case Builtin::BIstdc_count_ones_ui:
+ case Builtin::BIstdc_count_ones_ul:
+ case Builtin::BIstdc_count_ones_ull:
+ case Builtin::BI__builtin_stdc_count_ones:
+ return emitBuiltinBitOp<cir::BitPopcountOp>(*this, e);
+
case Builtin::BI__builtin_clzs:
case Builtin::BI__builtin_clz:
case Builtin::BI__builtin_clzl:
diff --git a/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
index 1f127821673d2..e9d5b25a10f0e 100644
--- a/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
+++ b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
@@ -10,8 +10,8 @@ void test_stdc_trailing_zeros(unsigned long long x) {
// CHECK-NOT: poison_zero
// CHECK: cir.return
-void test_stdc_leading_zeros(unsigned x) {
- return __builtin_stdc_trailing_zeros(x);
+unsigned test_stdc_leading_zeros(unsigned x) {
+ return __builtin_stdc_leading_zeros(x);
}
// CHECK-LABEL: test_stdc_leading_zeros
@@ -19,7 +19,7 @@ void test_stdc_leading_zeros(unsigned x) {
// CHECK-NOT: poison_zero
// CHECK: cir.return
-void test_stdc_leading_zeros_ui(unsigned x) {
+unsigned test_stdc_leading_zeros_ui(unsigned x) {
return stdc_leading_zeros_ui(x);
}
@@ -27,3 +27,19 @@ void test_stdc_leading_zeros_ui(unsigned x) {
// CHECK: cir.clz
// CHECK-NOT: poison_zero
// CHECK: cir.return
+
+unsigned test_stdc_count_ones(unsigned x) {
+ return __builtin_stdc_count_ones(x);
+}
+
+// CHECK-LABEL: test_stdc_count_ones
+// CHECK: cir.popcount
+// CHECK: cir.return
+
+unsigned test_stdc_count_ones_ui(unsigned x) {
+ return stdc_count_ones_ui(x);
+}
+
+// CHECK-LABEL: test_stdc_count_ones_ui
+// CHECK: cir.popcount
+// CHECK: cir.return
>From 5b211d8555808aac69e9c6f1d388c2dbd40daafb Mon Sep 17 00:00:00 2001
From: Kunal Dubey <xakep8 at protonmail.com>
Date: Mon, 10 Aug 2026 18:21:43 +0530
Subject: [PATCH 4/4] [CIR] Lowering __builtin_stdc_bit_width
Added lowering for __builtin_stdc_bit_width by addition of helper
emitStdcBitWidth that does integer type width minus leading zero count.
Added tests for the same.
---
clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp | 28 +++++++++++++++++++
.../CIR/CodeGenBuiltins/builtin-stdc-bit.c | 24 +++++++++++++++-
2 files changed, 51 insertions(+), 1 deletion(-)
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index d27ace31cef78..aef5818084bc4 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -111,6 +111,26 @@ static RValue emitBuiltinBitOpWithFallback(CIRGenFunction &cgf,
return RValue::get(builder.createSelect(loc, isZero, fallbackValue, result));
}
+static RValue emitStdcBitWidth(CIRGenFunction &cfg, const CallExpr *e) {
+ CIRGenBuilderTy &builder = cfg.getBuilder();
+ mlir::Location loc = cfg.getLoc(e->getSourceRange());
+
+ mlir::Value arg = cfg.emitScalarExpr(e->getArg(0));
+ auto argTy = mlir::cast<cir::IntType>(arg.getType());
+
+ mlir::Value lz =
+ createBuiltinBitOp<cir::BitClzOp>(cfg, e, arg, /*poisonZero=*/false);
+
+ mlir::Value width = builder.getConstInt(loc, argTy, argTy.getWidth());
+ mlir::Value result = builder.createSub(loc, width, lz);
+
+ mlir::Type resultTy = cfg.convertType(e->getType());
+ if (result.getType() != resultTy)
+ result = builder.createIntCast(result, resultTy);
+
+ return RValue::get(result);
+}
+
/// Emit the conversions required to turn the given value into an
/// integer of the given size.
static mlir::Value emitToInt(CIRGenFunction &cgf, mlir::Value v, QualType t,
@@ -1263,6 +1283,14 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
case Builtin::BI__builtin_stdc_leading_zeros:
return emitBuiltinBitOp<cir::BitClzOp>(*this, e, /*poisonZero=*/false);
+ case Builtin::BIstdc_bit_width_uc:
+ case Builtin::BIstdc_bit_width_us:
+ case Builtin::BIstdc_bit_width_ui:
+ case Builtin::BIstdc_bit_width_ul:
+ case Builtin::BIstdc_bit_width_ull:
+ case Builtin::BI__builtin_stdc_bit_width:
+ return emitStdcBitWidth(*this, e);
+
case Builtin::BIstdc_count_ones_uc:
case Builtin::BIstdc_count_ones_us:
case Builtin::BIstdc_count_ones_ui:
diff --git a/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
index e9d5b25a10f0e..56632e70761ef 100644
--- a/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
+++ b/clang/test/CIR/CodeGenBuiltins/builtin-stdc-bit.c
@@ -1,4 +1,6 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -std=c23 -I%S/../../CodeGen/Inputs -fclangir -emit-cir %s -o - | FileCheck %s
+
+#include <stdbit.h>
void test_stdc_trailing_zeros(unsigned long long x) {
int cnt = __builtin_stdc_trailing_zeros(x);
@@ -43,3 +45,23 @@ unsigned test_stdc_count_ones_ui(unsigned x) {
// CHECK-LABEL: test_stdc_count_ones_ui
// CHECK: cir.popcount
// CHECK: cir.return
+
+unsigned test_stdc_bit_width(unsigned x) {
+ return __builtin_stdc_bit_width(x);
+}
+
+// CHECK-LABEL: test_stdc_bit_width
+// CHECK: cir.clz
+// CHECK-NOT: poison_zero
+// CHECK: cir.sub
+// CHECK: cir.return
+
+unsigned test_stdc_bit_width_ui(unsigned x) {
+ return stdc_bit_width_ui(x);
+}
+
+// CHECK-LABEL: test_stdc_bit_width_ui
+// CHECK: cir.clz
+// CHECK-NOT: poison_zero
+// CHECK: cir.sub
+// CHECK: cir.return
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