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Do not fold away subreg_to_reg if the source register has a sub-register index. That means the source register is taking a sub-register of a larger register. e.g. On x86

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%RAX<def> = ...
%RAX<def> = SUBREG_TO_REG 0, %EAX:3<kill>, 3
The first def is defining RAX, not EAX so the top bits were not zero-extended.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67511 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2009-03-23 07:19:58 +00:00
parent a8bd27ff66
commit 7d6d4b360f
2 changed files with 34 additions and 3 deletions
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12
lib/CodeGen/LowerSubregs.cpp
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@ -165,11 +165,12 @@ bool LowerSubregsInstructionPass::LowerSubregToReg(MachineInstr *MI) {
unsigned DstReg = MI->getOperand(0).getReg();
unsigned InsReg = MI->getOperand(2).getReg();
unsigned SubIdx = MI->getOperand(3).getImm();
unsigned InsSIdx = MI->getOperand(2).getSubReg();
unsigned SubIdx = MI->getOperand(3).getImm();
assert(SubIdx != 0 && "Invalid index for insert_subreg");
unsigned DstSubReg = TRI.getSubReg(DstReg, SubIdx);
assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
"Insert destination must be in a physical register");
assert(TargetRegisterInfo::isPhysicalRegister(InsReg) &&
@ -177,8 +178,13 @@ bool LowerSubregsInstructionPass::LowerSubregToReg(MachineInstr *MI) {
DOUT << "subreg: CONVERTING: " << *MI;
if (DstSubReg == InsReg) {
if (DstSubReg == InsReg && InsSIdx == 0) {
// No need to insert an identify copy instruction.
// Watch out for case like this:
// %RAX<def> = ...
// %RAX<def> = SUBREG_TO_REG 0, %EAX:3<kill>, 3
// The first def is defining RAX, not EAX so the top bits were not
// zero extended.
DOUT << "subreg: eliminated!";
} else {
// Insert sub-register copy