Extended Description

The new test test/CodeGen/X86/licm-regpressure.ll shows this behavior (currently marked as XFAIL). MachineLICM assumes that it is hoisting all of the GEPs out of the loop under in a low pressure situation, when indeed there is register pressure.

The cause here is that the RegLimit (for the RegClass GR64) is 12, but each instruction is assumed to have a cost of only 1.

The problem seems to be that MachineLICM isn't considering the regmasks, i.e. the registers clobbered by the call.

IR leading to the bad behavior:

%struct.A = type { i32, i32, i32, i32, i32, i32, i32 }

define void @​test(i1 %b, %struct.A* %a) nounwind {
entry:
br label %loop-header

loop-header:
br label %loop-body

loop-body:
%0 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 0
%1 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 1
%2 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 2
%3 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 3
%4 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 4
%5 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 5
%6 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 6
call void @​assign(i32* %0)
call void @​assign(i32* %1)
call void @​assign(i32* %2)
call void @​assign(i32* %3)
call void @​assign(i32* %4)
call void @​assign(i32* %5)
call void @​assign(i32* %6)
br i1 %b, label %loop-body, label %loop-exit

loop-exit:
ret void
}

declare void @​assign(i32*)