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LowerSubregsInstructionPass::LowerExtract should not extend the live range of registers.

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When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the
kill flag to the place where the sub-register is killed. This can accidentally
overlap with the use of a sibling sub-register, and we have trouble.

In the test case we have this code:

Live Ins: %R0 %R1 %R2
	%R2L<def> = EXTRACT_SUBREG %R2<kill>, 1
	%R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0]
	%R1L<def> = EXTRACT_SUBREG %R1<kill>, 1
	%R0L<def> = EXTRACT_SUBREG %R0<kill>, 1
	%R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def>

subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1
subreg: eliminated!
subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def>

The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H:

*** Bad machine code: Redefining a live physical register ***
- function:    f
- basic block:  0x18358c0 (#0)
- instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0]
Register R2H was defined but already live.

The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating
it completely:

subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1
subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill>

Note that these IMPLICIT_DEF instructions survive to the asm output. It is
necessary to fix the stack-color-with-reg test case because of that.

llvm-svn: 78093
This commit is contained in:
Jakob Stoklund Olesen 2009-08-04 20:01:11 +00:00
parent 9824928578
commit 434f6a8d64
3 changed files with 27 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
lib/CodeGen/LowerSubregs.cpp
View File

@ -103,7 +103,7 @@ bool LowerSubregsInstructionPass::LowerExtract(MachineInstr *MI) {
MachineFunction &MF = *MBB->getParent();
const TargetRegisterInfo &TRI = *MF.getTarget().getRegisterInfo();
const TargetInstrInfo &TII = *MF.getTarget().getInstrInfo();
assert(MI->getOperand(0).isReg() && MI->getOperand(0).isDef() &&
MI->getOperand(1).isReg() && MI->getOperand(1).isUse() &&
MI->getOperand(2).isImm() && "Malformed extract_subreg");
@ -117,23 +117,20 @@ bool LowerSubregsInstructionPass::LowerExtract(MachineInstr *MI) {
"Extract supperg source must be a physical register");
assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
"Extract destination must be in a physical register");
DOUT << "subreg: CONVERTING: " << *MI;
if (SrcReg == DstReg) {
// No need to insert an identify copy instruction.
// No need to insert an identity copy instruction.
if (MI->getOperand(1).isKill()) {
// We must make sure the super-register gets killed.Replace the
// instruction with IMPLICIT_DEF.
MI->setDesc(TII.get(TargetInstrInfo::IMPLICIT_DEF));
MI->RemoveOperand(2); // SubIdx
DOUT << "subreg: replace by: " << *MI;
return true;
}
DOUT << "subreg: eliminated!";
// Find the kill of the destination register's live range, and insert
// a kill of the source register at that point.
if (MI->getOperand(1).isKill() && !MI->getOperand(0).isDead())
for (MachineBasicBlock::iterator MII =
next(MachineBasicBlock::iterator(MI));
MII != MBB->end(); ++MII)
if (MII->killsRegister(DstReg, &TRI)) {
MII->addRegisterKilled(SuperReg, &TRI, /*AddIfNotFound=*/true);
DOUT << "\nsubreg: killed here: " << *MII;
break;
}
} else {
// Insert copy
const TargetRegisterClass *TRCS = TRI.getPhysicalRegisterRegClass(DstReg);

15
test/CodeGen/Blackfin/2009-08-04-LowerExtract-Live.ll Normal file
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@ -0,0 +1,15 @@
; RUN: llvm-as < %s | llc -march=bfin -join-liveintervals=0 -verify-machineinstrs
; Provoke an error in LowerSubregsPass::LowerExtract where the live range of a
; super-register is illegally extended.
define i16 @f(i16 %x1, i16 %x2, i16 %x3, i16 %x4) {
%y1 = add i16 %x1, 1
%y2 = add i16 %x2, 2
%y3 = add i16 %x3, 3
%y4 = add i16 %x4, 4
%z12 = add i16 %y1, %y2
%z34 = add i16 %y3, %y4
%p = add i16 %z12, %z34
ret i16 %p
}

2
test/CodeGen/X86/stack-color-with-reg.ll
View File

@ -1,7 +1,7 @@
; RUN: llvm-as < %s | llc -mtriple=x86_64-apple-darwin10 -relocation-model=pic -disable-fp-elim -color-ss-with-regs -stats -info-output-file - > %t
; RUN: grep stackcoloring %t | grep "loads eliminated"
; RUN: grep stackcoloring %t | grep "stack slot refs replaced with reg refs" | grep 5
; RUN: grep asm-printer %t | grep 175
; RUN: grep asm-printer %t | grep 180
type { [62 x %struct.Bitvec*] } ; type %0
type { i8* } ; type %1