[clang] functions with the 'const' or 'pure' attribute must always return.

As described in
* https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute
* https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-const-function-attribute

An `__attribute__((pure))` function must always return, as well as an `__attribute__((const))` function.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D96960

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 405b4d2..992e873 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1994,9 +1994,14 @@ void CodeGenModule::ConstructAttributeList(
     if (TargetDecl->hasAttr<ConstAttr>()) {
       FuncAttrs.addAttribute(llvm::Attribute::ReadNone);
       FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);
+      // gcc specifies that 'const' functions have greater restrictions than
+      // 'pure' functions, so they also cannot have infinite loops.
+      FuncAttrs.addAttribute(llvm::Attribute::WillReturn);
     } else if (TargetDecl->hasAttr<PureAttr>()) {
       FuncAttrs.addAttribute(llvm::Attribute::ReadOnly);
       FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);
+      // gcc specifies that 'pure' functions cannot have infinite loops.
+      FuncAttrs.addAttribute(llvm::Attribute::WillReturn);
     } else if (TargetDecl->hasAttr<NoAliasAttr>()) {
       FuncAttrs.addAttribute(llvm::Attribute::ArgMemOnly);
       FuncAttrs.addAttribute(llvm::Attribute::NoUnwind);