[llvm] [RISCV] Don't add duplicate Zilsd hints. (PR #169554)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

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

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

This matches what ARM does. I'm not sure if there are any bad effects from the duplicate hints. I have seen the duplicates hints in the debug output and confirmed this removes them.

---
Full diff: https://github.com/llvm/llvm-project/pull/169554.diff


1 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp (+4-2) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp b/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
index a5aef4bea46ab..d802d19a0edcb 100644
--- a/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVRegisterInfo.cpp
@@ -869,6 +869,7 @@ bool RISCVRegisterInfo::getRegAllocationHints(
   unsigned HintType = Hint.first;
   Register Partner = Hint.second;
 
+  MCRegister TargetReg;
   if (HintType == RISCVRI::RegPairEven || HintType == RISCVRI::RegPairOdd) {
     // Check if we want the even or odd register of a consecutive pair
     bool WantOdd = (HintType == RISCVRI::RegPairOdd);
@@ -877,7 +878,7 @@ bool RISCVRegisterInfo::getRegAllocationHints(
     if (Partner.isVirtual() && VRM && VRM->hasPhys(Partner)) {
       MCRegister PartnerPhys = VRM->getPhys(Partner);
       // Calculate the exact register we need for consecutive pairing
-      MCRegister TargetReg = PartnerPhys.id() + (WantOdd ? 1 : -1);
+      TargetReg = PartnerPhys.id() + (WantOdd ? 1 : -1);
 
       // Verify it's valid and available
       if (RISCV::GPRRegClass.contains(TargetReg) &&
@@ -888,7 +889,8 @@ bool RISCVRegisterInfo::getRegAllocationHints(
     // Second priority: Try to find consecutive register pairs in the allocation
     // order
     for (MCPhysReg PhysReg : Order) {
-      if (!PhysReg)
+      // Don't add the hint if we already added above.
+      if (TargetReg == PhysReg)
         continue;
 
       unsigned RegNum = getEncodingValue(PhysReg);

``````````

</details>


https://github.com/llvm/llvm-project/pull/169554