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Fix MachineSink to be able to sink instructions that use physical registers

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which have no defs anywhere in the function. In particular, this fixes sinking
of instructions that reference RIP on x86-64, which is currently being modeled
as a register.

llvm-svn: 82815
This commit is contained in:
Dan Gohman 2009-09-25 22:53:29 +00:00
parent 35078c311e
commit 7c98ffa2b6
2 changed files with 32 additions and 1 deletions
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15
lib/CodeGen/MachineSink.cpp
View File

@ -35,6 +35,7 @@ namespace {
class VISIBILITY_HIDDEN MachineSinking : public MachineFunctionPass {
const TargetMachine *TM;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
MachineFunction *CurMF; // Current MachineFunction
MachineRegisterInfo *RegInfo; // Machine register information
MachineDominatorTree *DT; // Machine dominator tree
@ -95,6 +96,7 @@ bool MachineSinking::runOnMachineFunction(MachineFunction &MF) {
CurMF = &MF;
TM = &CurMF->getTarget();
TII = TM->getInstrInfo();
TRI = TM->getRegisterInfo();
RegInfo = &CurMF->getRegInfo();
DT = &getAnalysis<MachineDominatorTree>();
@ -176,8 +178,19 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
// If this is a physical register use, we can't move it. If it is a def,
// we can move it, but only if the def is dead.
if (MO.isUse() || !MO.isDead())
if (MO.isUse()) {
// If the physreg has no defs anywhere, it's just an ambient register
// and we can freely move its uses.
if (!RegInfo->def_empty(Reg))
return false;
// Check for a def among the register's aliases too.
for (const unsigned *Alias = TRI->getAliasSet(Reg); *Alias; ++Alias)
if (!RegInfo->def_empty(*Alias))
return false;
} else if (!MO.isDead()) {
// A def that isn't dead. We can't move it.
return false;
}
} else {
// Virtual register uses are always safe to sink.
if (MO.isUse()) continue;

18
test/CodeGen/X86/sink.ll Normal file
View File

@ -0,0 +1,18 @@
; RUN: llc < %s -march=x86-64 -asm-verbose=false | FileCheck %s
; Currently, floating-point selects are lowered to CFG triangles.
; This means that one side of the select is always unconditionally
; evaluated, however with MachineSink we can sink the other side so
; that it's conditionally evaluated.
; CHECK: foo:
; CHECK-NEXT: divsd
; CHECK-NEXT: testb $1, %dil
; CHECK-NEXT: jne
define double @foo(double %x, double %y, i1 %c) nounwind {
%a = fdiv double %x, 3.2
%b = fdiv double %y, 3.3
%z = select i1 %c, double %a, double %b
ret double %z
}