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Infer alignment of loads and increase their alignment when we can tell they are

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from the stack.  This allows us to compile stack-align.ll to:

_test:
	movsd	LCPI1_0, %xmm0
	movapd	%xmm0, %xmm1
***	andpd	4(%esp), %xmm1
	andpd	_G, %xmm0
	addsd	%xmm1, %xmm0
	movl	20(%esp), %eax
	movsd	%xmm0, (%eax)
	ret

instead of:

_test:
	movsd	LCPI1_0, %xmm0
**	movsd	4(%esp), %xmm1
**	andpd	%xmm0, %xmm1
	andpd	_G, %xmm0
	addsd	%xmm1, %xmm0
	movl	20(%esp), %eax
	movsd	%xmm0, (%eax)
	ret



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@46401 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-01-26 19:45:50 +00:00
parent 216f3f6522
commit 1329cb8d89
2 changed files with 55 additions and 4 deletions
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37
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -18,6 +18,7 @@
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetFrameInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
@ -4073,12 +4074,40 @@ bool DAGCombiner::CombineToPostIndexedLoadStore(SDNode *N) {
static unsigned InferAlignment(SDOperand Ptr, SelectionDAG &DAG) {
// If this is a direct reference to a stack slot, use information about the
// stack slot's alignment.
int FrameIdx = 1 << 31;
int64_t FrameOffset = 0;
if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Ptr)) {
return DAG.getMachineFunction().getFrameInfo()->
getObjectAlignment(FI->getIndex());
FrameIdx = FI->getIndex();
} else if (Ptr.getOpcode() == ISD::ADD &&
isa<ConstantSDNode>(Ptr.getOperand(1)) &&
isa<FrameIndexSDNode>(Ptr.getOperand(0))) {
FrameIdx = cast<FrameIndexSDNode>(Ptr.getOperand(0))->getIndex();
FrameOffset = Ptr.getConstantOperandVal(1);
}
if (FrameIdx != (1 << 31)) {
// FIXME: Handle FI+CST.
const MachineFrameInfo &MFI = *DAG.getMachineFunction().getFrameInfo();
if (MFI.isFixedObjectIndex(FrameIdx)) {
int64_t ObjectOffset = MFI.getObjectOffset(FrameIdx);
// The alignment of the frame index can be determined from its offset from
// the incoming frame position. If the frame object is at offset 32 and
// the stack is guaranteed to be 16-byte aligned, then we know that the
// object is 16-byte aligned.
unsigned StackAlign = DAG.getTarget().getFrameInfo()->getStackAlignment();
unsigned Align = MinAlign(ObjectOffset, StackAlign);
// Finally, the frame object itself may have a known alignment. Factor
// the alignment + offset into a new alignment. For example, if we know
// the FI is 8 byte aligned, but the pointer is 4 off, we really have a
// 4-byte alignment of the resultant pointer. Likewise align 4 + 4-byte
// offset = 4-byte alignment, align 4 + 1-byte offset = align 1, etc.
unsigned FIInfoAlign = MinAlign(MFI.getObjectAlignment(FrameIdx),
FrameOffset);
return std::max(Align, FIInfoAlign);
}
}
// FIXME: Handle FI+CST.
return 0;
}

22
test/CodeGen/X86/stack-align.ll Normal file
View File

@ -0,0 +1,22 @@
; RUN: llvm-as < %s | llc -relocation-model=static -mcpu=yonah | grep {andpd.*4(%esp), %xmm}
; The double argument is at 4(esp) which is 16-byte aligned, allowing us to
; fold the load into the andpd.
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"
@G = external global double
define void @test({ double, double }* byval %z, double* %P) {
entry:
%tmp = getelementptr { double, double }* %z, i32 0, i32 0 ; <double*> [#uses=1]
%tmp1 = load double* %tmp, align 8 ; <double> [#uses=1]
%tmp2 = tail call double @fabs( double %tmp1 ) ; <double> [#uses=1]
%tmp3 = load double* @G, align 16 ; <double> [#uses=1]
%tmp4 = tail call double @fabs( double %tmp3 ) ; <double> [#uses=1]
%tmp6 = add double %tmp4, %tmp2 ; <double> [#uses=1]
store double %tmp6, double* %P, align 8
ret void
}
declare double @fabs(double)