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AArch64: refactor frame handling to use movz/movk for overlarge offsets.

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In the near future litpools will be in a different section, which means that
any access to them is at least two instructions. This makes the case for a
movz/movk pair (if total offset <= 32-bits) even more compelling.

llvm-svn: 175257
This commit is contained in:
Tim Northover 2013-02-15 09:33:26 +00:00
parent ce14af1162
commit 9f3ff5cc4c
2 changed files with 42 additions and 28 deletions
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39
lib/Target/AArch64/AArch64InstrInfo.cpp
View File

@ -623,18 +623,35 @@ void llvm::emitRegUpdate(MachineBasicBlock &MBB,
else if (abs(NumBytes) & ~0xffffff) {
// Generically, we have to materialize the offset into a temporary register
// and subtract it. There are a couple of ways this could be done, for now
// we'll go for a literal-pool load.
MachineFunction &MF = *MBB.getParent();
MachineConstantPool *MCP = MF.getConstantPool();
const Constant *C
= ConstantInt::get(Type::getInt64Ty(MF.getFunction()->getContext()),
abs(NumBytes));
unsigned CPI = MCP->getConstantPoolIndex(C, 8);
// we'll use a movz/movk or movn/movk sequence.
uint64_t Bits = static_cast<uint64_t>(abs(NumBytes));
BuildMI(MBB, MBBI, dl, TII.get(AArch64::MOVZxii), ScratchReg)
.addImm(0xffff & Bits).addImm(0)
.setMIFlags(MIFlags);
// LDR xTMP, .LITPOOL
BuildMI(MBB, MBBI, dl, TII.get(AArch64::LDRx_lit), ScratchReg)
.addConstantPoolIndex(CPI)
.setMIFlag(MIFlags);
Bits >>= 16;
if (Bits & 0xffff) {
BuildMI(MBB, MBBI, dl, TII.get(AArch64::MOVKxii), ScratchReg)
.addReg(ScratchReg)
.addImm(0xffff & Bits).addImm(1)
.setMIFlags(MIFlags);
}
Bits >>= 16;
if (Bits & 0xffff) {
BuildMI(MBB, MBBI, dl, TII.get(AArch64::MOVKxii), ScratchReg)
.addReg(ScratchReg)
.addImm(0xffff & Bits).addImm(2)
.setMIFlags(MIFlags);
}
Bits >>= 16;
if (Bits & 0xffff) {
BuildMI(MBB, MBBI, dl, TII.get(AArch64::MOVKxii), ScratchReg)
.addReg(ScratchReg)
.addImm(0xffff & Bits).addImm(3)
.setMIFlags(MIFlags);
}
// ADD DST, SRC, xTMP (, lsl #0)
unsigned AddOp = NumBytes > 0 ? AArch64::ADDxxx_uxtx : AArch64::SUBxxx_uxtx;

31
test/CodeGen/AArch64/large-frame.ll
View File

@ -11,17 +11,22 @@ define void @test_bigframe() {
%var3 = alloca i8, i32 20000000
; CHECK: sub sp, sp, #496
; CHECK: str x30, [sp, #488]
; CHECK: ldr [[FRAMEOFFSET:x[0-9]+]], [[FRAMEOFFSET_CPI:.LCPI0_[0-9]+]]
; CHECK: sub sp, sp, [[FRAMEOFFSET]]
; Total adjust is 39999536
; CHECK: movz [[SUBCONST:x[0-9]+]], #22576
; CHECK: movk [[SUBCONST]], #610, lsl #16
; CHECK: sub sp, sp, [[SUBCONST]]
; CHECK: ldr [[VAR1OFFSET:x[0-9]+]], [[VAR1LOC_CPI:.LCPI0_[0-9]+]]
; Total offset is 20000024
; CHECK: movz [[VAR1OFFSET:x[0-9]+]], #11544
; CHECK: movk [[VAR1OFFSET]], #305, lsl #16
; CHECK: add {{x[0-9]+}}, sp, [[VAR1OFFSET]]
store volatile i8* %var1, i8** @addr
%var1plus2 = getelementptr i8* %var1, i32 2
store volatile i8* %var1plus2, i8** @addr
; CHECK: ldr [[VAR2OFFSET:x[0-9]+]], [[VAR2LOC_CPI:.LCPI0_[0-9]+]]
; CHECK: movz [[VAR2OFFSET:x[0-9]+]], #11528
; CHECK: movk [[VAR2OFFSET]], #305, lsl #16
; CHECK: add {{x[0-9]+}}, sp, [[VAR2OFFSET]]
store volatile i8* %var2, i8** @addr
@ -33,18 +38,10 @@ define void @test_bigframe() {
%var3plus2 = getelementptr i8* %var3, i32 2
store volatile i8* %var3plus2, i8** @addr
; CHECK: ldr [[FRAMEOFFSET:x[0-9]+]], [[FRAMEOFFSET_CPI]]
; CHECK: add sp, sp, [[FRAMEOFFSET]]
; CHECK: movz [[ADDCONST:x[0-9]+]], #22576
; CHECK: movk [[ADDCONST]], #610, lsl #16
; CHECK: add sp, sp, [[ADDCONST]]
ret void
; CHECK: [[FRAMEOFFSET_CPI]]:
; CHECK-NEXT: 39999536
; CHECK: [[VAR1LOC_CPI]]:
; CHECK-NEXT: 20000024
; CHECK: [[VAR2LOC_CPI]]:
; CHECK-NEXT: 20000008
}
define void @test_mediumframe() {
@ -103,10 +100,10 @@ define void @test_tempallocation([8 x i64] %val) nounwind {
; CHECK-NEXT: stp x19, x20, [sp,
; Make sure we don't trash an argument register
; CHECK-NOT: ldr {{x[0-7]}}, .LCPI1
; CHECK-NOT: movz {{x[0-7],}}
; CHECK: sub sp, sp,
; CHECK-NOT: ldr {{x[0-7]}}, .LCPI1
; CHECK-NOT: movz {{x[0-7],}}
; CHECK: bl use_addr
call void @use_addr(i8* %var)