Clean up scavengeRegister() a bit to prefer available regs, which allows

the simplification of frame index register scavenging to not have to check
for available registers directly and instead just let scavengeRegister()
handle it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107880 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/PrologEpilogInserter.cpp b/lib/CodeGen/PrologEpilogInserter.cpp
index d1112d3c14aaaf50184087ab3ec62445c81c9106..3843b2537051ce0a64345518f932ef7634b2e03a 100644 (file)
--- a/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/lib/CodeGen/PrologEpilogInserter.cpp
@@ -885,21 +885,7 @@ void PEI::scavengeFrameVirtualRegs(MachineFunction &Fn) {
             // Scavenge a new scratch register
             CurrentVirtReg = Reg;
             const TargetRegisterClass *RC = Fn.getRegInfo().getRegClass(Reg);
-            const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
-            BitVector Candidates(TRI->getNumRegs());
-            RS->getRegsAvailable(RC, Candidates);
-
-            // If there are any registers available, use the one that's
-            // unused for the longest after this instruction. That increases
-            // the ability to reuse the value.
-            if (Candidates.any()) {
-              MachineBasicBlock::iterator UMI;
-              CurrentScratchReg = RS->findSurvivorReg(I, Candidates, 25, UMI);
-            } else {
-              // No register is "free". Scavenge a register.
-              CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
-            }
-
+            CurrentScratchReg = RS->scavengeRegister(RC, I, SPAdj);
             PrevValue = Value;
           }
           // replace this reference to the virtual register with the

diff --git a/lib/CodeGen/RegisterScavenging.cpp b/lib/CodeGen/RegisterScavenging.cpp
index 8a1ef5adf7909cd7fae1f90e78d6ea7309d7c17a..43b3fb642635149d4a00574b5e35266ea8a01d83 100644 (file)
--- a/lib/CodeGen/RegisterScavenging.cpp
+++ b/lib/CodeGen/RegisterScavenging.cpp
@@ -339,13 +339,16 @@ unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
       Candidates.reset(MO.getReg());
   }
 
+  // Try to find a register that's unused if there is one, as then we won't
+  // have to spill.
+  if ((Candidates & RegsAvailable).any())
+     Candidates &= RegsAvailable;
+
   // Find the register whose use is furthest away.
   MachineBasicBlock::iterator UseMI;
   unsigned SReg = findSurvivorReg(I, Candidates, 25, UseMI);
 
-  // If we found an unused register there is no reason to spill it. We have
-  // probably found a callee-saved register that has been saved in the
-  // prologue, but happens to be unused at this point.
+  // If we found an unused register there is no reason to spill it.
   if (!isAliasUsed(SReg))
     return SReg;