From 2be0fae98c54ff6b0e7a53ee1d01b5a402eaa51e Mon Sep 17 00:00:00 2001 From: Andrew Trick Date: Thu, 6 Feb 2014 19:20:41 +0000 Subject: Track register pressure a bit more carefully (weird corner case). This solves a problem where a def machine operand has no uses but has not been marked dead. In this case, the initial RP analysis was being extra precise and determining from LiveIntervals the the register was actually dead. This caused us to omit the register from the RP tracker's block live out. That's all good, but the per-instruction summary still accounted for it as a valid def. This could cause an assertion in the tracker later when we underflow pressure. This is from a bug report on an out-of-tree target. It is not reproducible on well-behaved targets. I'm just making an obvious fix without unit test. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200941 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/RegisterPressure.cpp | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/CodeGen/RegisterPressure.cpp b/lib/CodeGen/RegisterPressure.cpp index 092ecdd9bb..249789a4b1 100644 --- a/lib/CodeGen/RegisterPressure.cpp +++ b/lib/CodeGen/RegisterPressure.cpp @@ -506,7 +506,14 @@ bool RegPressureTracker::recede(SmallVectorImpl *LiveUses, DeadDef = LRQ.isDeadDef(); } } - if (!DeadDef) { + if (DeadDef) { + // LiveIntervals knows this is a dead even though it's MachineOperand is + // not flagged as such. Since this register will not be recorded as + // live-out, increase its PDiff value to avoid underflowing pressure. + if (PDiff) + PDiff->addPressureChange(Reg, false, MRI); + } + else { if (LiveRegs.erase(Reg)) decreaseRegPressure(Reg); else -- cgit v1.2.3