[InlineSpiller] Drop unused elements in Virt2SiblingsMap. NFC

[csstormq]

No description provided.

[llvmbot]

@llvm/pr-subscribers-llvm-regalloc

Author: None (csstormq)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/147866.diff

1 Files Affected:

• (modified) llvm/lib/CodeGen/InlineSpiller.cpp (+1-1)

diff --git a/llvm/lib/CodeGen/InlineSpiller.cpp b/llvm/lib/CodeGen/InlineSpiller.cpp
index ee08dc42dce57..18ec0bc1c050c 100644
--- a/llvm/lib/CodeGen/InlineSpiller.cpp
+++ b/llvm/lib/CodeGen/InlineSpiller.cpp
@@ -1657,7 +1657,7 @@ void HoistSpillHelper::hoistAllSpills() {
   for (unsigned i = 0, e = MRI.getNumVirtRegs(); i != e; ++i) {
     Register Reg = Register::index2VirtReg(i);
     Register Original = VRM.getPreSplitReg(Reg);
-    if (!MRI.def_empty(Reg))
+    if (!MRI.def_empty(Reg) && Original.id())
       Virt2SiblingsMap[Original].insert(Reg);
   }
 

[arsenm]

I don't understand this. 0 isn't an invalid register index, it's the first valid virtual register index.

[csstormq]

I don't understand this. 0 isn't an invalid register index, it's the first valid virtual register index.

@arsenm , thanks for your review. In my opinion, the key of Virt2SiblingsMap (the original register) should always hold the equal value as its corresponding value (the sibling register). However, the getPreSplitReg function returns 0, register number rather than register index, when encountering a register that was not created by splitting. Consequently, Virt2SiblingsMap[0] ends up storing registers with differing values, which directly contradicts the map's design principle.

[arsenm]

However, the getPreSplitReg function returns 0, register number rather than register index, when encountering a register that was not created by splitting.

As in Register()? You shouldn't be checking against .id() == 0 for that case, rely on bool conversion?

[csstormq]

As in Register()? You shouldn't be checking against .id() == 0 for that case, rely on bool conversion?

Thanks for the advice. I’ve updated the code accordingly.