https://llvm.org/bugs/show_bug.cgi?id=23143
Bug ID: 23143
Summary: MachineLICM register pressure calculation incorrect
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Common Code Generator Code
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
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*)
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