[PATCH] D132181: [X86][AArch64][NFC] Simplify querying used argument registers

[Bill Wendling via Phabricator via llvm-commits]

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Registers used for arguments are listed as "live-ins" into the starting
basic block. This means we don't have to go through a potentially
expensive search through all possible argument registers when we only
care about used argument registers.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D132181

Files:
  llvm/lib/CodeGen/PrologEpilogInserter.cpp


Index: llvm/lib/CodeGen/PrologEpilogInserter.cpp
===================================================================
--- llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -1206,6 +1206,11 @@
             UsedRegs.set(Reg);
         }
 
+  // Get a list of registers that are used.
+  BitVector LiveIns(TRI.getNumRegs());
+  for (const auto &LI : MF.front().liveins())
+    LiveIns.set(LI.PhysReg);
+
   BitVector RegsToZero(TRI.getNumRegs());
   for (MCRegister Reg : AllocatableSet.set_bits()) {
     // Skip over fixed registers.
@@ -1221,8 +1226,14 @@
       continue;
 
     // Want only registers used for arguments.
-    if (OnlyArg && !TRI.isArgumentRegister(MF, Reg))
-      continue;
+    if (OnlyArg) {
+      if (OnlyUsed) {
+        if (!LiveIns[Reg])
+          continue;
+      } else if (!TRI.isArgumentRegister(MF, Reg)) {
+        continue;
+      }
+    }
 
     RegsToZero.set(Reg);
   }


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