[llvm] [RISCV] Convert an assertion to an if condition in getRegAllocationHints (PR #85998)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

With GPR pairs from Zdinx, we can't guarantee there are no subregisters on integer instruction operands. I've been able to get these assertions to fire after some other recent PRs.

I've added a FIXME to support this properly. I just wanted to prevent the assertion failure for now.

No test case because my other patch that allowed me to fail the assert hasn't been approved yet, and I don't know for that that patch is required to hit this assert. It's just want exposed it for me. So I think this patch is a good precaution regardless.

---
Full diff: https://github.com/llvm/llvm-project/pull/85998.diff


1 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp (+5-2) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp b/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
index 10bf1e88d74146..952d17468da590 100644
--- a/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
@@ -741,8 +741,11 @@ bool RISCVRegisterInfo::getRegAllocationHints(
                         bool NeedGPRC) -> void {
     Register Reg = MO.getReg();
     Register PhysReg = Reg.isPhysical() ? Reg : Register(VRM->getPhys(Reg));
-    if (PhysReg && (!NeedGPRC || RISCV::GPRCRegClass.contains(PhysReg))) {
-      assert(!MO.getSubReg() && !VRRegMO.getSubReg() && "Unexpected subreg!");
+    // TODO: Support GPRPair subregisters? Need to be careful with even/odd
+    // registers. If the virtual register is an odd register of a pair and the
+    // physical register is even (or vice versa), we should not add the hint.
+    if (PhysReg && (!NeedGPRC || RISCV::GPRCRegClass.contains(PhysReg)) &&
+        !MO.getSubReg() && !VRRegMO.getSubReg()) {
       if (!MRI->isReserved(PhysReg) && !is_contained(Hints, PhysReg))
         TwoAddrHints.insert(PhysReg);
     }

``````````

</details>


https://github.com/llvm/llvm-project/pull/85998