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Only use clairvoyance when defining a register, and then only if it has one use.

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This makes allocation independent on the ordering of use-def chains.

llvm-svn: 103935
This commit is contained in:
Jakob Stoklund Olesen 2010-05-17 04:50:57 +00:00
parent f7bef21e58
commit 40545bf117
2 changed files with 16 additions and 25 deletions
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27
lib/CodeGen/RegAllocFast.cpp
View File

@ -399,20 +399,6 @@ void RAFast::allocVirtReg(MachineInstr *MI, LiveRegEntry &LRE, unsigned Hint) {
!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 @@ RAFast::defineVirtReg(MachineInstr *MI, unsigned OpNum,
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;

14
test/CodeGen/PowerPC/2007-04-30-InlineAsmEarlyClobber.ll
View File

@ -1,15 +1,11 @@
; RUN: llc < %s | FileCheck %s
; RUN: llc < %s -regalloc=local | FileCheck -check-prefix=LOCAL %s
; RUN: llc < %s -regalloc=fast | FileCheck -check-prefix=FAST %s
; RUN: llc < %s -regalloc=local | FileCheck %s
; RUN: llc < %s -regalloc=fast | FileCheck %s
; The first argument of subfc must not be the same as any other register.
; CHECK: subfc r3,r5,r4
; CHECK: subfze r4,r6
; LOCAL: subfc r6,r5,r4
; LOCAL: subfze r3,r3
; FAST: subfc r3,r5,r4
; FAST: subfze r4,r6
; CHECK: subfc [[REG:r.]],
; CHECK-NOT: [[REG]]
; CHECK: InlineAsm End
; PR1357
target datalayout = "E-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64"