[clang] [clang] constexpr built-in elementwise popcount function. (PR #117473)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (c8ef)

<details>
<summary>Changes</summary>

Part of #<!-- -->51787.

This patch adds constexpr support for the built-in elementwise popcount function.

---
Full diff: https://github.com/llvm/llvm-project/pull/117473.diff


4 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+1) 
- (modified) clang/include/clang/Basic/Builtins.td (+1-1) 
- (modified) clang/lib/AST/ExprConstant.cpp (+30) 
- (modified) clang/test/Sema/constant_builtins_vector.cpp (+5) 


``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8bd06fadfdc984..16a151da38bb5d 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -370,6 +370,7 @@ Non-comprehensive list of changes in this release
 - ``__builtin_reduce_mul`` function can now be used in constant expressions.
 - ``__builtin_reduce_and`` function can now be used in constant expressions.
 - ``__builtin_reduce_or`` and ``__builtin_reduce_xor`` functions can now be used in constant expressions.
+- ``__builtin_elementwise_popcount`` function can now be used in constant expressions.
 
 New Compiler Flags
 ------------------
diff --git a/clang/include/clang/Basic/Builtins.td b/clang/include/clang/Basic/Builtins.td
index 83c90b3d6e681b..246250442ef62c 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -1354,7 +1354,7 @@ def ElementwiseLog10 : Builtin {
 
 def ElementwisePopcount : Builtin {
   let Spellings = ["__builtin_elementwise_popcount"];
-  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Attributes = [NoThrow, Const, CustomTypeChecking, Constexpr];
   let Prototype = "void(...)";
 }
 
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index c6a210459240a8..8a3ced30be9440 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -11005,6 +11005,7 @@ namespace {
     bool VisitUnaryImag(const UnaryOperator *E);
     bool VisitBinaryOperator(const BinaryOperator *E);
     bool VisitUnaryOperator(const UnaryOperator *E);
+    bool VisitCallExpr(const CallExpr *E);
     bool VisitConvertVectorExpr(const ConvertVectorExpr *E);
     bool VisitShuffleVectorExpr(const ShuffleVectorExpr *E);
 
@@ -11302,6 +11303,35 @@ static bool handleVectorElementCast(EvalInfo &Info, const FPOptions FPO,
   return false;
 }
 
+bool VectorExprEvaluator::VisitCallExpr(const CallExpr *E) {
+  if (!IsConstantEvaluatedBuiltinCall(E))
+    return ExprEvaluatorBaseTy::VisitCallExpr(E);
+
+  switch (E->getBuiltinCallee()) {
+  default:
+    return false;
+  case Builtin::BI__builtin_elementwise_popcount: {
+    APValue Source;
+    if (!EvaluateAsRValue(Info, E->getArg(0), Source))
+      return false;
+
+    QualType DestTy = E->getType()->castAs<VectorType>()->getElementType();
+    unsigned SourceLen = Source.getVectorLength();
+    SmallVector<APValue, 4> ResultElements;
+    ResultElements.reserve(SourceLen);
+
+    for (unsigned EltNum = 0; EltNum < SourceLen; ++EltNum) {
+      APSInt Elt = Source.getVectorElt(EltNum).getInt();
+      ResultElements.push_back(
+          APValue(APSInt(APInt(Info.Ctx.getIntWidth(DestTy), Elt.popcount()),
+                         DestTy->isUnsignedIntegerOrEnumerationType())));
+    }
+
+    return Success(APValue(ResultElements.data(), ResultElements.size()), E);
+  }
+  }
+}
+
 bool VectorExprEvaluator::VisitConvertVectorExpr(const ConvertVectorExpr *E) {
   APValue Source;
   QualType SourceVecType = E->getSrcExpr()->getType();
diff --git a/clang/test/Sema/constant_builtins_vector.cpp b/clang/test/Sema/constant_builtins_vector.cpp
index e84d09b24672b4..76d8bdfda3690a 100644
--- a/clang/test/Sema/constant_builtins_vector.cpp
+++ b/clang/test/Sema/constant_builtins_vector.cpp
@@ -797,3 +797,8 @@ static_assert(__builtin_reduce_xor((vector4int){(int)0x11111111, (int)0x22222222
 static_assert(__builtin_reduce_xor((vector4long){(long long)0x1111111111111111L, (long long)0x2222222222222222L, (long long)0x4444444444444444L, (long long)0x8888888888888888L}) == (long long)0xFFFFFFFFFFFFFFFFL);
 static_assert(__builtin_reduce_xor((vector4uint){0x11111111U, 0x22222222U, 0x44444444U, 0x88888888U}) == 0xFFFFFFFFU);
 static_assert(__builtin_reduce_xor((vector4ulong){0x1111111111111111UL, 0x2222222222222222UL, 0x4444444444444444UL, 0x8888888888888888UL}) == 0xFFFFFFFFFFFFFFFFUL);
+
+static_assert(__builtin_reduce_add(__builtin_elementwise_popcount((vector4int){1, 2, 3, 4})) == 5);
+static_assert(__builtin_reduce_add(__builtin_elementwise_popcount((vector4int){0, 0xF0F0, ~0, ~0xF0F0})) == 16 * sizeof(int));
+static_assert(__builtin_reduce_add(__builtin_elementwise_popcount((vector4long){1L, 2L, 3L, 4L})) == 5L);
+static_assert(__builtin_reduce_add(__builtin_elementwise_popcount((vector4long){0L, 0xF0F0L, ~0L, ~0xF0F0L})) == 16 * sizeof(long long));

``````````

</details>


https://github.com/llvm/llvm-project/pull/117473