[llvm] [CodeGen] Allocate RegAllocHints map lazily (PR #102186)

[Craig Topper via llvm-commits]

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@@ -801,6 +801,7 @@ class MachineRegisterInfo {
   /// of an earlier hint it will be overwritten.
   void setRegAllocationHint(Register VReg, unsigned Type, Register PrefReg) {
     assert(VReg.isVirtual());
+    RegAllocHints.grow(Register::index2VirtReg(getNumVirtRegs()));
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topperc wrote:

Should this be `getNumVirtRegs() - 1`? `grow` expects an index. getNumVRegs() is one past the largest index. Or maybe we could use `resize`?

https://github.com/llvm/llvm-project/pull/102186