[MIR-Canon] Skip the first N vreg names lazily.

[plotfi]

Summary

This consolidates the vreg skip code into one function (SkipVRegs()). SkipVRegs() now knows if it should skip as if it is the first initialization or subsequent skips.

[compnerd]

llvm/lib/CodeGen/MIRCanonicalizerPass.cpp

483 ↗

(On Diff #202368)

Why not just initialize in the initializer list?

[plotfi]

llvm/lib/CodeGen/MIRCanonicalizerPass.cpp

483 ↗

(On Diff #202368)

I can do that too.

[plotfi]

using initializer list.

llvm/trunk/lib/CodeGen/MIRCanonicalizerPass.cpp

 }
 
 namespace {
 class NamedVRegCursor {
   MachineRegisterInfo &MRI;
   unsigned virtualVRegNumber;
 
 public:
-  NamedVRegCursor(MachineRegisterInfo &MRI) : MRI(MRI) {
-    unsigned VRegGapIndex = 0;
-    const unsigned VR_GAP = (++VRegGapIndex * 1000);
-
-    unsigned I = MRI.createIncompleteVirtualRegister();
-    const unsigned E = (((I + VR_GAP) / VR_GAP) + 1) * VR_GAP;
-
-    virtualVRegNumber = E;
-  }
+  NamedVRegCursor(MachineRegisterInfo &MRI) : MRI(MRI), virtualVRegNumber(0) {}
 
   void SkipVRegs() {
     unsigned VRegGapIndex = 1;
+    if (!virtualVRegNumber) {
+      VRegGapIndex = 0;
+      virtualVRegNumber = MRI.createIncompleteVirtualRegister();
+    }
     const unsigned VR_GAP = (++VRegGapIndex * 1000);
 
     unsigned I = virtualVRegNumber;
     const unsigned E = (((I + VR_GAP) / VR_GAP) + 1) * VR_GAP;
 
     virtualVRegNumber = E;
   }
 
   unsigned getVirtualVReg() const { return virtualVRegNumber; }
 
   unsigned incrementVirtualVReg(unsigned incr = 1) {
     virtualVRegNumber += incr;
     return virtualVRegNumber;
   }
 
   unsigned createVirtualRegister(unsigned VReg) {
+    if (!virtualVRegNumber)
+      SkipVRegs();
     std::string S;
     raw_string_ostream OS(S);
     OS << "namedVReg" << (virtualVRegNumber & ~0x80000000);
     OS.flush();
     virtualVRegNumber++;
     if (auto RC = MRI.getRegClassOrNull(VReg))
       return MRI.createVirtualRegister(RC, OS.str());
     return MRI.createGenericVirtualRegister(MRI.getType(VReg), OS.str());

llvm/trunk/test/CodeGen/MIR/AArch64/multiple-lhs-operands.mir

 # RUN: llc -mtriple=aarch64-none-linux-gnu -run-pass none -o - %s | FileCheck %s
 # This test ensures that the MIR parser can parse multiple register machine
 # operands before '='.
 
+# This tests that a MIR file with no vregs does not get altered by mir-canon.
+# RUN: llc -mtriple=aarch64 -o - -run-pass mir-canonicalizer -verify-machineinstrs %s
+
 --- |
 
   declare void @foo()
 
   define void @trivial_fp_func() {
   entry:
     call void @foo()
     ret void