From 65eb2f394cd8ee7aaee0ea9b5e0ed76407347f30 Mon Sep 17 00:00:00 2001 From: Mikael Holmen Date: Wed, 4 Oct 2017 06:06:31 +0000 Subject: [UnreachableBlockElim] Use COPY if PHI input is undef Summary: If we have %vreg0 = PHI %vreg2, , %vreg3, ; GR32:%vreg0,%vreg2,%vreg3 %vreg3 = ADD32ri8 %vreg0, 1, %EFLAGS; GR32:%vreg3,%vreg0 then we can't just change %vreg0 into %vreg3, since %vreg2 is actually undef. We would have to also copy the undef flag to be able to change the register. Instead we deal with this case like other cases where we can't just replace the register: we insert a COPY. The code creating the COPY already copied all flags from the PHI input, so the undef flag will be transferred as it should. Reviewers: kparzysz Reviewed By: kparzysz Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D38235 llvm-svn: 314879 --- llvm/lib/CodeGen/UnreachableBlockElim.cpp | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'llvm/lib/CodeGen/UnreachableBlockElim.cpp') diff --git a/llvm/lib/CodeGen/UnreachableBlockElim.cpp b/llvm/lib/CodeGen/UnreachableBlockElim.cpp index 407fd9b162e..bdd25f29aea 100644 --- a/llvm/lib/CodeGen/UnreachableBlockElim.cpp +++ b/llvm/lib/CodeGen/UnreachableBlockElim.cpp @@ -207,11 +207,12 @@ bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) { MachineRegisterInfo &MRI = F.getRegInfo(); unsigned InputSub = Input.getSubReg(); if (InputSub == 0 && - MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg))) { + MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg)) && + !Input.isUndef()) { MRI.replaceRegWith(OutputReg, InputReg); } else { // The input register to the PHI has a subregister or it can't be - // constrained to the proper register class: + // constrained to the proper register class or it is undef: // insert a COPY instead of simply replacing the output // with the input. const TargetInstrInfo *TII = F.getSubtarget().getInstrInfo(); -- cgit v1.2.3