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Mark rematerialized super/sub registers as dead.

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When we're rematerializing into a not-quite-right register we already add the
real definition as an imp-def, but we should also be marking the "official"
register as dead, since nothing else is going to use it as a result of this
remat.

Not doing this can affect pressure tracking.

rdar://problem/14158833

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184002 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Tim Northover 2013-06-14 20:22:21 +00:00
parent d5d7410982
commit 89dbe97442
2 changed files with 24 additions and 0 deletions
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1
lib/CodeGen/RegisterCoalescer.cpp
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@ -843,6 +843,7 @@ bool RegisterCoalescer::reMaterializeTrivialDef(CoalescerPair &CP,
// been asked for. If so it must implicitly define the whole thing.
assert(TargetRegisterInfo::isPhysicalRegister(DstReg) &&
"Only expect virtual or physical registers in remat");
NewMI->getOperand(0).setIsDead(true);
NewMI->addOperand(MachineOperand::CreateReg(CopyDstReg,
true /*IsDef*/,
true /*IsImp*/,

23
test/CodeGen/X86/remat-phys-dead.ll Normal file
View File

@ -0,0 +1,23 @@
; REQUIRES: asserts
; RUN: llc -mtriple=x86_64-apple-darwin -debug -o /dev/null < %s 2>&1 | FileCheck %s
; We need to make sure that rematerialization into a physical register marks the
; super- or sub-register as dead after this rematerialization since only the
; original register is actually used later. Largely irrelevant for a trivial
; example like this, since EAX is never used again, but easy to test.
define i8 @test_remat() {
ret i8 0
; CHECK: REGISTER COALESCING
; CHECK: Remat: %EAX<def,dead> = MOV32r0 %EFLAGS<imp-def,dead>, %AL<imp-def>
}
; On the other hand, if it's already the correct width, we really shouldn't be
; marking the definition register as dead.
define i32 @test_remat32() {
ret i32 0
; CHECK: REGISTER COALESCING
; CHECK: Remat: %EAX<def> = MOV32r0 %EFLAGS<imp-def,dead>
}