[RISCV] Guard the alternative static chain register use on ILP32E/LP64E (#142715)

Asserts the use of t3(x28) as the static chain register when branch control flow protection is enabled with ILP32E/LP64E, because such register is not present within the ABI.

Author: jaidTw

llvm/lib/Target/RISCV/RISCVCallingConv.cpp

@@ -333,15 +333,23 @@ bool llvm::CC_RISCV(unsigned ValNo, MVT ValVT, MVT LocVT,
   unsigned XLen = Subtarget.getXLen();
   MVT XLenVT = Subtarget.getXLenVT();
 
-  // Static chain parameter must not be passed in normal argument registers,
-  // so we assign t2/t3 for it as done in GCC's __builtin_call_with_static_chain
-  bool HasCFBranch =
-      Subtarget.hasStdExtZicfilp() &&
-      MF.getFunction().getParent()->getModuleFlag("cf-protection-branch");
-  // Normal: t2, Branch control flow protection: t3
-  const auto StaticChainReg = HasCFBranch ? RISCV::X28 : RISCV::X7;
-
   if (ArgFlags.isNest()) {
+    // Static chain parameter must not be passed in normal argument registers,
+    // so we assign t2/t3 for it as done in GCC's
+    // __builtin_call_with_static_chain
+    bool HasCFBranch =
+        Subtarget.hasStdExtZicfilp() &&
+        MF.getFunction().getParent()->getModuleFlag("cf-protection-branch");
+
+    // Normal: t2, Branch control flow protection: t3
+    const auto StaticChainReg = HasCFBranch ? RISCV::X28 : RISCV::X7;
+
+    RISCVABI::ABI ABI = Subtarget.getTargetABI();
+    if (HasCFBranch &&
+        (ABI == RISCVABI::ABI_ILP32E || ABI == RISCVABI::ABI_LP64E))
+      reportFatalUsageError(
+          "Nested functions with control flow protection are not "
+          "usable with ILP32E or LP64E ABI.");
     if (MCRegister Reg = State.AllocateReg(StaticChainReg)) {
       State.addLoc(CCValAssign::getReg(ValNo, ValVT, Reg, LocVT, LocInfo));
       return false;

llvm/test/CodeGen/RISCV/nest-register.ll

@@ -5,6 +5,8 @@
 ; RUN:   | FileCheck -check-prefix=RV64I %s
 ; RUN: llc -mtriple=riscv64 -mattr=+experimental-zicfilp -verify-machineinstrs < %s \
 ; RUN:   | FileCheck -check-prefix=RV64I-ZICFILP %s
+; RUN: not llc -mtriple=riscv64 -target-abi=lp64e -mattr=+experimental-zicfilp \
+; RUN:   -verify-machineinstrs < %s 2>&1 | FileCheck -check-prefix=LP64E-ZICFILP %s
 
 ; Tests that the 'nest' parameter attribute causes the relevant parameter to be
 ; passed in the right register.
@@ -63,6 +65,7 @@ define ptr @nest_caller(ptr %arg) nounwind {
   ret ptr %result
 }
 
+; LP64E-ZICFILP: LLVM ERROR: Nested functions with control flow protection are not usable with ILP32E or LP64E ABI.
 !llvm.module.flags = !{!0}
 
 !0 = !{i32 8, !"cf-protection-branch", i32 1}