Only use clairvoyance when defining a register, and then only if it has one use.
This makes allocation independent on the ordering of use-def chains.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103935 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocFast.cpp b/lib/CodeGen/RegAllocFast.cpp
index 9449780..04aa47e 100644
--- a/lib/CodeGen/RegAllocFast.cpp
+++ b/lib/CodeGen/RegAllocFast.cpp
@@ -399,20 +399,6 @@
!Allocatable.test(Hint)))
Hint = 0;
- // If there is no hint, peek at the first use of this register.
- if (!Hint && !MRI->use_nodbg_empty(VirtReg)) {
- MachineInstr &MI = *MRI->use_nodbg_begin(VirtReg);
- unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
- // Copy to physreg -> use physreg as hint.
- if (TII->isMoveInstr(MI, SrcReg, DstReg, SrcSubReg, DstSubReg) &&
- SrcReg == VirtReg && TargetRegisterInfo::isPhysicalRegister(DstReg) &&
- RC->contains(DstReg) && !UsedInInstr.test(DstReg) &&
- Allocatable.test(DstReg)) {
- Hint = DstReg;
- DEBUG(dbgs() << "%reg" << VirtReg << " gets hint from " << MI);
- }
- }
-
// Take hint when possible.
if (Hint) {
assert(RC->contains(Hint) && !UsedInInstr.test(Hint) &&
@@ -543,9 +529,18 @@
bool New;
tie(LRI, New) = LiveVirtRegs.insert(std::make_pair(VirtReg, LiveReg()));
LiveReg &LR = LRI->second;
- if (New)
+ if (New) {
+ // If there is no hint, peek at the only use of this register.
+ if ((!Hint || !TargetRegisterInfo::isPhysicalRegister(Hint)) &&
+ MRI->hasOneNonDBGUse(VirtReg)) {
+ unsigned SrcReg, DstReg, SrcSubReg, DstSubReg;
+ // It's a copy, use the destination register as a hint.
+ if (TII->isMoveInstr(*MRI->use_nodbg_begin(VirtReg),
+ SrcReg, DstReg, SrcSubReg, DstSubReg))
+ Hint = DstReg;
+ }
allocVirtReg(MI, *LRI, Hint);
- else
+ } else
addKillFlag(LR); // Kill before redefine.
assert(LR.PhysReg && "Register not assigned");
LR.LastUse = MI;