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Re-enable elimination of unnecessary SUBREG_TO_REG instructions in

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LowerSubregs, and fix an x86-64 isel bug that this exposed.

SUBREG_TO_REG for x86-64 implicit zero extension is only safe for
isel to generate when the source is known to always have zeros in
the high 32 bits. The EXTRACT_SUBREG instruction does not clear
the high 32 bits.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@54444 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2008-08-07 02:54:50 +00:00
parent 865db4566e
commit e3d920699c
5 changed files with 46 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
lib/CodeGen/LowerSubregs.cpp
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@ -108,15 +108,20 @@ bool LowerSubregsInstructionPass::LowerSubregToReg(MachineInstr *MI) {
DOUT << "subreg: CONVERTING: " << *MI;
// Insert sub-register copy
const TargetRegisterClass *TRC0= TRI.getPhysicalRegisterRegClass(DstSubReg);
const TargetRegisterClass *TRC1= TRI.getPhysicalRegisterRegClass(InsReg);
TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
if (DstSubReg == InsReg) {
// No need to insert an identify copy instruction.
DOUT << "subreg: eliminated!";
} else {
// Insert sub-register copy
const TargetRegisterClass *TRC0= TRI.getPhysicalRegisterRegClass(DstSubReg);
const TargetRegisterClass *TRC1= TRI.getPhysicalRegisterRegClass(InsReg);
TII.copyRegToReg(*MBB, MI, DstSubReg, InsReg, TRC0, TRC1);
#ifndef NDEBUG
MachineBasicBlock::iterator dMI = MI;
DOUT << "subreg: " << *(--dMI);
#endif
}
DOUT << "\n";
MBB->erase(MI);