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avoid going through a stack slot to convert from fpstack to xmm reg

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if we are just going to store it back anyway.  This improves things 
like:
double foo();
void bar(double *P) { *P = foo(); }



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45399 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-12-29 06:41:28 +00:00
parent 3c87285af6
commit 112dedc520
3 changed files with 54 additions and 29 deletions
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21
lib/Target/X86/README.txt
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@ -1636,24 +1636,3 @@ a stride-4 IV, would would allow all the scales in the loop to go away.
This would result in smaller code and more efficient microops.
//===---------------------------------------------------------------------===//
We should be smarter about conversion from fpstack to XMM regs.
double foo();
void bar(double *P) { *P = foo(); }
We compile that to:
_bar:
subl $12, %esp
call L_foo$stub
fstpl (%esp)
movl 16(%esp), %eax
movsd (%esp), %xmm0
movsd %xmm0, (%eax)
addl $12, %esp
ret
for example. The magic to/from the stack is unneeded.
//===---------------------------------------------------------------------===//

47
lib/Target/X86/X86ISelLowering.cpp
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@ -33,7 +33,6 @@
#include "llvm/CodeGen/SelectionDAG.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/ADT/SmallSet.h"
@ -812,7 +811,6 @@ LowerCallResult(SDOperand Chain, SDOperand InFlag, SDNode *TheCall,
CCState CCInfo(CallingConv, isVarArg, getTargetMachine(), RVLocs);
CCInfo.AnalyzeCallResult(TheCall, RetCC_X86);
SmallVector<SDOperand, 8> ResultVals;
// Copy all of the result registers out of their specified physreg.
@ -838,17 +836,50 @@ LowerCallResult(SDOperand Chain, SDOperand InFlag, SDNode *TheCall,
// an XMM register.
if ((X86ScalarSSEf32 && RVLocs[0].getValVT() == MVT::f32) ||
(X86ScalarSSEf64 && RVLocs[0].getValVT() == MVT::f64)) {
SDOperand StoreLoc;
const Value *SrcVal = 0;
int SrcValOffset = 0;
// Determine where to store the value. If the call result is directly
// used by a store, see if we can store directly into the location. In
// this case, we'll end up producing a fst + movss[load] + movss[store] to
// the same location, and the two movss's will be nuked as dead. This
// optimizes common things like "*D = atof(..)" to not need an
// intermediate stack slot.
if (SDOperand(TheCall, 0).hasOneUse() &&
SDOperand(TheCall, 1).hasOneUse()) {
// Ok, we have one use of the value and one use of the chain. See if
// they are the same node: a store.
if (StoreSDNode *N = dyn_cast<StoreSDNode>(*TheCall->use_begin())) {
if (N->getChain().Val == TheCall && N->getValue().Val == TheCall &&
!N->isVolatile() && !N->isTruncatingStore() &&
N->getAddressingMode() == ISD::UNINDEXED) {
StoreLoc = N->getBasePtr();
SrcVal = N->getSrcValue();
SrcValOffset = N->getSrcValueOffset();
}
}
}
// If we weren't able to optimize the result, just create a temporary
// stack slot.
if (StoreLoc.Val == 0) {
MachineFunction &MF = DAG.getMachineFunction();
int SSFI = MF.getFrameInfo()->CreateStackObject(8, 8);
StoreLoc = DAG.getFrameIndex(SSFI, getPointerTy());
}
// FIXME: Currently the FST is flagged to the FP_GET_RESULT. This
// shouldn't be necessary except that RFP cannot be live across
// multiple blocks. When stackifier is fixed, they can be uncoupled.
MachineFunction &MF = DAG.getMachineFunction();
int SSFI = MF.getFrameInfo()->CreateStackObject(8, 8);
SDOperand StackSlot = DAG.getFrameIndex(SSFI, getPointerTy());
// multiple blocks (which could happen if a select gets lowered into
// multiple blocks and scheduled in between them). When stackifier is
// fixed, they can be uncoupled.
SDOperand Ops[] = {
Chain, RetVal, StackSlot, DAG.getValueType(RVLocs[0].getValVT()), InFlag
Chain, RetVal, StoreLoc, DAG.getValueType(RVLocs[0].getValVT()), InFlag
};
Chain = DAG.getNode(X86ISD::FST, MVT::Other, Ops, 5);
RetVal = DAG.getLoad(RVLocs[0].getValVT(), Chain, StackSlot, NULL, 0);
RetVal = DAG.getLoad(RVLocs[0].getValVT(), Chain,
StoreLoc, SrcVal, SrcValOffset);
Chain = RetVal.getValue(1);
}
ResultVals.push_back(RetVal);

15
test/CodeGen/X86/fp-stack-ret-store.ll Normal file
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@ -0,0 +1,15 @@
; RUN: llvm-as < %s | llc | not grep movss
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i686-apple-darwin8"
; This should store directly into P from the FP stack. It should not
; go through a stack slot to get there.
define void @bar(double* %P) {
entry:
%tmp = tail call double (...)* @foo( ) ; <double> [#uses=1]
store double %tmp, double* %P, align 8
ret void
}
declare double @foo(...)