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[PowerPC][ELFv2ABI] Allocate parameter area on-demand to reduce stack…
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… frame size

This patch reduces the stack frame size by not allocating the parameter area if
it is not required. In the current implementation LowerFormalArguments_64SVR4
already handles the parameter area, but LowerCall_64SVR4 does not
(when calculating the stack frame size). What this patch does is make
LowerCall_64SVR4 consistent with LowerFormalArguments_64SVR4.

Committing on behalf of Hiroshi Inoue.

Differential Revision: https://reviews.llvm.org/D29881

llvm-svn: 296771
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@nemanjai
nemanjai committed Mar 2, 2017
1 parent 21bef2c commit db8425e
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Showing 2 changed files with 129 additions and 5 deletions.
48 changes: 43 additions & 5 deletions llvm/lib/Target/PowerPC/PPCISelLowering.cpp
View file
Expand Up @@ -5147,10 +5147,30 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
};

const unsigned NumGPRs = array_lengthof(GPR);
const unsigned NumFPRs = 13;
const unsigned NumFPRs = useSoftFloat() ? 0 : 13;
const unsigned NumVRs = array_lengthof(VR);
const unsigned NumQFPRs = NumFPRs;

// On ELFv2, we can avoid allocating the parameter area if all the arguments
// can be passed to the callee in registers.
// For the fast calling convention, there is another check below.
// Note: keep consistent with LowerFormalArguments_64SVR4()
bool HasParameterArea = !isELFv2ABI || isVarArg || CallConv == CallingConv::Fast;
if (!HasParameterArea) {
unsigned ParamAreaSize = NumGPRs * PtrByteSize;
unsigned AvailableFPRs = NumFPRs;
unsigned AvailableVRs = NumVRs;
unsigned NumBytesTmp = NumBytes;
for (unsigned i = 0; i != NumOps; ++i) {
if (Outs[i].Flags.isNest()) continue;
if (CalculateStackSlotUsed(Outs[i].VT, Outs[i].ArgVT, Outs[i].Flags,
PtrByteSize, LinkageSize, ParamAreaSize,
NumBytesTmp, AvailableFPRs, AvailableVRs,
Subtarget.hasQPX()))
HasParameterArea = true;
}
}

// When using the fast calling convention, we don't provide backing for
// arguments that will be in registers.
unsigned NumGPRsUsed = 0, NumFPRsUsed = 0, NumVRsUsed = 0;
Expand Down Expand Up @@ -5218,13 +5238,18 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(

unsigned NumBytesActuallyUsed = NumBytes;

// The prolog code of the callee may store up to 8 GPR argument registers to
// In the old ELFv1 ABI,
// the prolog code of the callee may store up to 8 GPR argument registers to
// the stack, allowing va_start to index over them in memory if its varargs.
// Because we cannot tell if this is needed on the caller side, we have to
// conservatively assume that it is needed. As such, make sure we have at
// least enough stack space for the caller to store the 8 GPRs.
// FIXME: On ELFv2, it may be unnecessary to allocate the parameter area.
NumBytes = std::max(NumBytes, LinkageSize + 8 * PtrByteSize);
// In the ELFv2 ABI, we allocate the parameter area iff a callee
// really requires memory operands, e.g. a vararg function.
if (HasParameterArea)
NumBytes = std::max(NumBytes, LinkageSize + 8 * PtrByteSize);
else
NumBytes = LinkageSize;

// Tail call needs the stack to be aligned.
if (getTargetMachine().Options.GuaranteedTailCallOpt &&
Expand Down Expand Up @@ -5443,6 +5468,8 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
if (CallConv == CallingConv::Fast)
ComputePtrOff();

assert(HasParameterArea &&
"Parameter area must exist to pass an argument in memory.");
LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
true, isTailCall, false, MemOpChains,
TailCallArguments, dl);
Expand Down Expand Up @@ -5528,6 +5555,8 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
PtrOff = DAG.getNode(ISD::ADD, dl, PtrVT, PtrOff, ConstFour);
}

assert(HasParameterArea &&
"Parameter area must exist to pass an argument in memory.");
LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
true, isTailCall, false, MemOpChains,
TailCallArguments, dl);
Expand Down Expand Up @@ -5562,6 +5591,8 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
// GPRs when within range. For now, we always put the value in both
// locations (or even all three).
if (isVarArg) {
assert(HasParameterArea &&
"Parameter area must exist if we have a varargs call.");
// We could elide this store in the case where the object fits
// entirely in R registers. Maybe later.
SDValue Store =
Expand Down Expand Up @@ -5594,6 +5625,8 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
if (CallConv == CallingConv::Fast)
ComputePtrOff();

assert(HasParameterArea &&
"Parameter area must exist to pass an argument in memory.");
LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
true, isTailCall, true, MemOpChains,
TailCallArguments, dl);
Expand All @@ -5614,6 +5647,8 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
case MVT::v4i1: {
bool IsF32 = Arg.getValueType().getSimpleVT().SimpleTy == MVT::v4f32;
if (isVarArg) {
assert(HasParameterArea &&
"Parameter area must exist if we have a varargs call.");
// We could elide this store in the case where the object fits
// entirely in R registers. Maybe later.
SDValue Store =
Expand Down Expand Up @@ -5646,6 +5681,8 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
if (CallConv == CallingConv::Fast)
ComputePtrOff();

assert(HasParameterArea &&
"Parameter area must exist to pass an argument in memory.");
LowerMemOpCallTo(DAG, MF, Chain, Arg, PtrOff, SPDiff, ArgOffset,
true, isTailCall, true, MemOpChains,
TailCallArguments, dl);
Expand All @@ -5660,7 +5697,8 @@ SDValue PPCTargetLowering::LowerCall_64SVR4(
}
}

assert(NumBytesActuallyUsed == ArgOffset);
assert((!HasParameterArea || NumBytesActuallyUsed == ArgOffset) &&
"mismatch in size of parameter area");
(void)NumBytesActuallyUsed;

if (!MemOpChains.empty())
Expand Down
86 changes: 86 additions & 0 deletions llvm/test/CodeGen/PowerPC/stacksize.ll
View file
@@ -0,0 +1,86 @@
; For ELFv2 ABI, we can avoid allocating the parameter area in the stack frame of the caller function
; if all the arguments can be passed to the callee in registers.
; For ELFv1 ABI, we always need to allocate the parameter area.

; Tests for ELFv2 ABI
; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu -target-abi elfv2 < %s | FileCheck %s -check-prefix=PPC64-ELFV2
; RUN: llc -verify-machineinstrs -mtriple=powerpc64-unknown-linux-gnu -target-abi elfv2 < %s | FileCheck %s -check-prefix=PPC64-ELFV2

; Tests for ELFv1 ABI
; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu -target-abi elfv1 < %s | FileCheck %s -check-prefix=PPC64-ELFV1
; RUN: llc -verify-machineinstrs -mtriple=powerpc64-unknown-linux-gnu -target-abi elfv1 < %s | FileCheck %s -check-prefix=PPC64-ELFV1

; If the callee has at most eight integer args, parameter area can be ommited for ELFv2 ABI.

; PPC64-ELFV2-LABEL: WithoutParamArea1:
; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV2: stdu 1, -32(1)
; PPC64-ELFV2: addi 1, 1, 32
; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1-LABEL: WithoutParamArea1:
; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1: stdu 1, -112(1)
; PPC64-ELFV1: addi 1, 1, 112
; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
define signext i32 @WithoutParamArea1(i32 signext %a) local_unnamed_addr #0 {
entry:
%call = tail call signext i32 @onearg(i32 signext %a) #2
ret i32 %call
}

; PPC64-ELFV2-LABEL: WithoutParamArea2:
; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV2: stdu 1, -32(1)
; PPC64-ELFV2: addi 1, 1, 32
; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1-LABEL: WithoutParamArea2:
; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1: stdu 1, -112(1)
; PPC64-ELFV1: addi 1, 1, 112
; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
define signext i32 @WithoutParamArea2(i32 signext %a) local_unnamed_addr #0 {
entry:
%call = tail call signext i32 @eightargs(i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a) #2
ret i32 %call
}

; If the callee has more than eight integer args or variable number of args,
; parameter area cannot be ommited even for ELFv2 ABI

; PPC64-ELFV2-LABEL: WithParamArea1:
; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV2: stdu 1, -96(1)
; PPC64-ELFV2: addi 1, 1, 96
; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1-LABEL: WithParamArea1:
; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1: stdu 1, -112(1)
; PPC64-ELFV1: addi 1, 1, 112
; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
define signext i32 @WithParamArea1(i32 signext %a) local_unnamed_addr #0 {
entry:
%call = tail call signext i32 (i32, ...) @varargs(i32 signext %a, i32 signext %a) #2
ret i32 %call
}

; PPC64-ELFV2-LABEL: WithParamArea2:
; PPC64-ELFV2-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV2: stdu 1, -112(1)
; PPC64-ELFV2: addi 1, 1, 112
; PPC64-ELFV2-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1-LABEL: WithParamArea2:
; PPC64-ELFV1-NOT: stw {{[0-9]+}}, -{{[0-9]+}}(1)
; PPC64-ELFV1: stdu 1, -128(1)
; PPC64-ELFV1: addi 1, 1, 128
; PPC64-ELFV1-NOT: lwz {{[0-9]+}}, -{{[0-9]+}}(1)
define signext i32 @WithParamArea2(i32 signext %a) local_unnamed_addr #0 {
entry:
%call = tail call signext i32 @nineargs(i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a, i32 signext %a) #2
ret i32 %call
}

declare signext i32 @onearg(i32 signext) local_unnamed_addr #1
declare signext i32 @eightargs(i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext) local_unnamed_addr #1
declare signext i32 @nineargs(i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext, i32 signext) local_unnamed_addr #1
declare signext i32 @varargs(i32 signext, ...) local_unnamed_addr #1

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