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When we look at instructions to convert to setting the 's' flag, we need to look

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at more than those which define CPSR. You can have this situation:

(1)  subs  ...
(2)  sub   r6, r5, r4
(3)  movge ...
(4)  cmp   r6, 0
(5)  movge ...

We cannot convert (2) to "subs" because (3) is using the CPSR set by
(1). There's an analogous situation here:

(1)  sub   r1, r2, r3
(2)  sub   r4, r5, r6
(3)  cmp   r4, ...
(5)  movge ...
(6)  cmp   r1, ...
(7)  movge ...

We cannot convert (1) to "subs" because of the intervening use of CPSR.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117950 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling
2010-11-01 20:41:43 +00:00
parent a37d5cf342
commit 40a5eb18b0
4 changed files with 23 additions and 18 deletions
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8
lib/Target/ARM/ARMBaseInstrInfo.cpp
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@@ -21,7 +21,6 @@
#include "llvm/Constants.h"
#include "llvm/Function.h"
#include "llvm/GlobalValue.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
@@ -34,6 +33,7 @@
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
static cl::opt<bool>
@@ -1557,10 +1557,10 @@ OptimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, int CmpMask,
for (unsigned IO = 0, EO = Instr.getNumOperands(); IO != EO; ++IO) {
const MachineOperand &MO = Instr.getOperand(IO);
if (!MO.isReg() || !MO.isDef()) continue;
if (!MO.isReg()) continue;
// This instruction modifies CPSR before the one we want to change. We
// can't do this transformation.
// This instruction modifies or uses CPSR after the one we want to
// change. We can't do this transformation.
if (MO.getReg() == ARM::CPSR)
return false;
}