From 2c420066da0e4f6abb2be21d0c24fbff6c928fb0 Mon Sep 17 00:00:00 2001
From: Bart Coppens <kde@bartcoppens.be>
Date: Fri, 12 Jan 2024 18:56:09 +0100
Subject: [PATCH 1/2] Add support for the llvm.is.constant.* intrinsics. (#185)

Add support for the llvm.is.constant.* intrinsics. According to the
LLVM LangRef, this intrinsic will never return true when constant
folding is not run, so always returning false is safe. Partially
resolves issue #149.
---
 lib/Target/CBackend/CBackend.cpp    | 6 ++++++
 test/cpp_tests/test_is_constant.cpp | 8 ++++++++
 2 files changed, 14 insertions(+)
 create mode 100644 test/cpp_tests/test_is_constant.cpp

diff --git a/lib/Target/CBackend/CBackend.cpp b/lib/Target/CBackend/CBackend.cpp
index 339e4a9b..98cb6986 100644
--- a/lib/Target/CBackend/CBackend.cpp
+++ b/lib/Target/CBackend/CBackend.cpp
@@ -2573,6 +2573,7 @@ void CWriter::generateHeader(Module &M) {
       case Intrinsic::trunc:
       case Intrinsic::umax:
       case Intrinsic::umin:
+      case Intrinsic::is_constant:
         intrinsicsToDefine.push_back(&*I);
         continue;
       }
@@ -4643,6 +4644,9 @@ void CWriter::printIntrinsicDefinition(FunctionType *funT, unsigned Opcode,
     case Intrinsic::umin:
       Out << "  r = a < b ? a : b;\n";
       break;
+    case Intrinsic::is_constant:
+      Out << "  r = 0 /* llvm.is.constant */;\n";
+      break;
     }
 
   } else {
@@ -4764,6 +4768,7 @@ bool CWriter::lowerIntrinsics(Function &F) {
           case Intrinsic::dbg_declare:
           case Intrinsic::umax:
           case Intrinsic::umin:
+          case Intrinsic::is_constant:
             // We directly implement these intrinsics
             break;
 
@@ -5078,6 +5083,7 @@ bool CWriter::visitBuiltinCall(CallInst &I, Intrinsic::ID ID) {
   case Intrinsic::trap:
   case Intrinsic::umax:
   case Intrinsic::umin:
+  case Intrinsic::is_constant:
     return false; // these use the normal function call emission
   }
 }
diff --git a/test/cpp_tests/test_is_constant.cpp b/test/cpp_tests/test_is_constant.cpp
new file mode 100644
index 00000000..e1e1f9f7
--- /dev/null
+++ b/test/cpp_tests/test_is_constant.cpp
@@ -0,0 +1,8 @@
+int f(int i) {
+  if (__builtin_constant_p(i) &&
+      i == 1) /* generates the llvm.is.constant.i32 intrinsic at -O0 */
+    return i + 5;
+  return 6;
+}
+
+int main() { return f(1); }

From 1bc2950a391b80ac6812f2c5101f04e052b5e861 Mon Sep 17 00:00:00 2001
From: Jameson Nash <vtjnash@gmail.com>
Date: Fri, 12 Jan 2024 14:22:29 -0500
Subject: [PATCH 2/2] build: explicit specify LLVM_DIR to cmake (#189)

---
 .github/workflows/main.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 5e289e19..e5ed6a75 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -65,7 +65,7 @@ jobs:
       - name: Build
         run: |
           mkdir build
-          cmake -S . -B build -DLLVM_INCLUDE_TESTS=On
+          cmake -S . -B build -DLLVM_INCLUDE_TESTS=On -DLLVM_DIR=/usr/lib/llvm-16/cmake
           cmake --build build
 
       - name: Test