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Implement the ldr-pseudo opcode for ARM assembly

The ldr-pseudo opcode is a convenience for loading 32-bit constants.
It is converted into a pc-relative load from a constant pool. For
example,

  ldr r0, =0x10001
  ldr r1, =bar

will generate this output in the final assembly

  ldr r0, .Ltmp0
  ldr r1, .Ltmp1
  ...
  .Ltmp0: .long 0x10001
  .Ltmp1: .long bar

Sketch of the LDR pseudo implementation:
  Keep a map from Section => ConstantPool

  When parsing ldr r0, =val
    parse val as an MCExpr
    get ConstantPool for current Section
    Label = CreateTempSymbol()
    remember val in ConstantPool at next free slot
    add operand to ldr that is MCSymbolRef of Label

  On finishParse() callback
    Write out all non-empty constant pools
    for each Entry in ConstantPool
      Emit Entry.Label
      Emit Entry.Value

Possible improvements to be added in a later patch:
  1. Does not convert load of small constants to mov
     (e.g. ldr r0, =0x1 => mov r0, 0x1)
  2. Does reuse constant pool entries for same constant

The implementation was tested for ARM, Thumb1, and Thumb2 targets on
linux and darwin.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197708 91177308-0d34-0410-b5e6-96231b3b80d8
  • Loading branch information...
dmpots committed Dec 19, 2013
1 parent 6075fa1 commit 0fa193b08627927ccaa0804a34d80480894614b8
@@ -36,6 +36,7 @@
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/SourceMgr.h"
@@ -50,11 +51,69 @@ class ARMOperand;

enum VectorLaneTy { NoLanes, AllLanes, IndexedLane };

// A class to keep track of assembler-generated constant pools that are use to
// implement the ldr-pseudo.
class ConstantPool {
typedef SmallVector<std::pair<MCSymbol *, const MCExpr *>, 4> EntryVecTy;
EntryVecTy Entries;

public:
// Initialize a new empty constant pool
ConstantPool() { }

// Add a new entry to the constant pool in the next slot.
// \param Value is the new entry to put in the constant pool.
//
// \returns a MCExpr that references the newly inserted value
const MCExpr *addEntry(const MCExpr *Value, MCContext &Context) {
MCSymbol *CPEntryLabel = Context.CreateTempSymbol();

Entries.push_back(std::make_pair(CPEntryLabel, Value));
return MCSymbolRefExpr::Create(CPEntryLabel, Context);
}

// Emit the contents of the constant pool using the provided streamer.
void emitEntries(MCStreamer &Streamer) const {
Streamer.EmitCodeAlignment(4); // align to 4-byte address
Streamer.EmitDataRegion(MCDR_DataRegion);
for (EntryVecTy::const_iterator I = Entries.begin(), E = Entries.end();
I != E; ++I) {
Streamer.EmitLabel(I->first);
Streamer.EmitValue(I->second, 4);
}
Streamer.EmitDataRegion(MCDR_DataRegionEnd);
}
};

// Map type used to keep track of per-Section constant pools used by the
// ldr-pseudo opcode. The map associates a section to its constant pool. The
// constant pool is a vector of (label, value) pairs. When the ldr
// pseudo is parsed we insert a new (label, value) pair into the constant pool
// for the current section and add MCSymbolRefExpr to the new label as
// an opcode to the ldr. After we have parsed all the user input we
// output the (label, value) pairs in each constant pool at the end of the
// section.
typedef std::map<const MCSection *, ConstantPool> ConstantPoolMapTy;

class ARMAsmParser : public MCTargetAsmParser {
MCSubtargetInfo &STI;
MCAsmParser &Parser;
const MCInstrInfo &MII;
const MCRegisterInfo *MRI;
ConstantPoolMapTy ConstantPools;

// Assembler created constant pools for ldr pseudo
ConstantPool *getConstantPool(const MCSection *Section) {
ConstantPoolMapTy::iterator CP = ConstantPools.find(Section);
if (CP == ConstantPools.end())
return 0;

return &CP->second;
}

ConstantPool &getOrCreateConstantPool(const MCSection *Section) {
return ConstantPools[Section];
}

ARMTargetStreamer &getTargetStreamer() {
MCTargetStreamer &TS = getParser().getStreamer().getTargetStreamer();
@@ -296,7 +355,7 @@ class ARMAsmParser : public MCTargetAsmParser {
MCStreamer &Out, unsigned &ErrorInfo,
bool MatchingInlineAsm);
void onLabelParsed(MCSymbol *Symbol);

void finishParse();
};
} // end anonymous namespace

@@ -4656,6 +4715,24 @@ bool ARMAsmParser::parseOperand(SmallVectorImpl<MCParsedAsmOperand*> &Operands,
Operands.push_back(ARMOperand::CreateImm(ExprVal, S, E));
return false;
}
case AsmToken::Equal: {
if (Mnemonic != "ldr") // only parse for ldr pseudo (e.g. ldr r0, =val)
return Error(Parser.getTok().getLoc(), "unexpected token in operand");

const MCSection *Section =
getParser().getStreamer().getCurrentSection().first;
assert(Section);
Parser.Lex(); // Eat '='
const MCExpr *SubExprVal;
if (getParser().parseExpression(SubExprVal))
return true;
E = SMLoc::getFromPointer(Parser.getTok().getLoc().getPointer() - 1);

const MCExpr *CPLoc =
getOrCreateConstantPool(Section).addEntry(SubExprVal, getContext());
Operands.push_back(ARMOperand::CreateImm(CPLoc, S, E));
return false;
}
}
}

@@ -8396,3 +8473,18 @@ unsigned ARMAsmParser::validateTargetOperandClass(MCParsedAsmOperand *AsmOp,
}
return Match_InvalidOperand;
}

void ARMAsmParser::finishParse() {
// Dump contents of assembler constant pools.
MCStreamer &Streamer = getParser().getStreamer();
for (ConstantPoolMapTy::iterator CPI = ConstantPools.begin(),
CPE = ConstantPools.end();
CPI != CPE; ++CPI) {
const MCSection *Section = CPI->first;
ConstantPool &CP = CPI->second;

// Dump assembler constant pools at the end of the section.
Streamer.SwitchSection(Section);
CP.emitEntries(Streamer);
}
}
@@ -0,0 +1,241 @@
@ This test has a partner (ldr-pseudo.s) that contains matching
@ tests for the ldr-pseudo on linux targets. We need separate files
@ because the syntax for switching sections and temporary labels differs
@ between darwin and linux. Any tests added here should have a matching
@ test added there.

@RUN: llvm-mc -triple armv7-apple-darwin %s | FileCheck %s
@RUN: llvm-mc -triple thumbv5-apple-darwin %s | FileCheck %s
@RUN: llvm-mc -triple thumbv7-apple-darwin %s | FileCheck %s

@
@ Check that large constants are converted to ldr from constant pool
@
@ simple test
.section __TEXT,b,regular,pure_instructions
@ CHECK-LABEL: f3:
f3:
ldr r0, =0x10001
@ CHECK: ldr r0, Ltmp0

@ loading multiple constants
.section __TEXT,c,regular,pure_instructions
@ CHECK-LABEL: f4:
f4:
ldr r0, =0x10002
@ CHECK: ldr r0, Ltmp1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
ldr r0, =0x10003
@ CHECK: ldr r0, Ltmp2
adds r0, r0, #1
adds r0, r0, #1

@ TODO: the same constants should have the same constant pool location
.section __TEXT,d,regular,pure_instructions
@ CHECK-LABEL: f5:
f5:
ldr r0, =0x10004
@ CHECK: ldr r0, Ltmp3
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
ldr r0, =0x10004
@ CHECK: ldr r0, Ltmp4
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1

@ a section defined in multiple pieces should be merged and use a single constant pool
.section __TEXT,e,regular,pure_instructions
@ CHECK-LABEL: f6:
f6:
ldr r0, =0x10006
@ CHECK: ldr r0, Ltmp5
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1

.section __TEXT,f,regular,pure_instructions
@ CHECK-LABEL: f7:
f7:
adds r0, r0, #1
adds r0, r0, #1
adds r0, r0, #1

.section __TEXT,e,regular,pure_instructions
@ CHECK-LABEL: f8:
f8:
adds r0, r0, #1
ldr r0, =0x10007
@ CHECK: ldr r0, Ltmp6
adds r0, r0, #1
adds r0, r0, #1

@
@ Check that symbols can be loaded using ldr pseudo
@

@ load an undefined symbol
.section __TEXT,g,regular,pure_instructions
@ CHECK-LABEL: f9:
f9:
ldr r0, =foo
@ CHECK: ldr r0, Ltmp7

@ load a symbol from another section
.section __TEXT,h,regular,pure_instructions
@ CHECK-LABEL: f10:
f10:
ldr r0, =f5
@ CHECK: ldr r0, Ltmp8

@ load a symbol from the same section
.section __TEXT,i,regular,pure_instructions
@ CHECK-LABEL: f11:
f11:
ldr r0, =f12
@ CHECK: ldr r0, Ltmp9

@ CHECK-LABEL: f12:
f12:
adds r0, r0, #1
adds r0, r0, #1

.section __TEXT,j,regular,pure_instructions
@ mix of symbols and constants
@ CHECK-LABEL: f13:
f13:
adds r0, r0, #1
adds r0, r0, #1
ldr r0, =0x101
@ CHECK: ldr r0, Ltmp10
adds r0, r0, #1
adds r0, r0, #1
ldr r0, =bar
@ CHECK: ldr r0, Ltmp11
adds r0, r0, #1
adds r0, r0, #1
@
@ Check for correct usage in other contexts
@

@ usage in macro
.macro useit_in_a_macro
ldr r0, =0x10008
ldr r0, =baz
.endm
.section __TEXT,k,regular,pure_instructions
@ CHECK-LABEL: f14:
f14:
useit_in_a_macro
@ CHECK: ldr r0, Ltmp12
@ CHECK: ldr r0, Ltmp13

@ usage with expressions
.section __TEXT,l,regular,pure_instructions
@ CHECK-LABEL: f15:
f15:
ldr r0, =0x10001+8
@ CHECK: ldr r0, Ltmp14
adds r0, r0, #1
ldr r0, =bar+4
@ CHECK: ldr r0, Ltmp15
adds r0, r0, #1

@
@ Constant Pools
@
@ CHECK: .section __TEXT,b,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp0:
@ CHECK: .long 65537
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,c,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp1:
@ CHECK: .long 65538
@ CHECK-LABEL: Ltmp2:
@ CHECK: .long 65539
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,d,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp3:
@ CHECK: .long 65540
@ CHECK-LABEL: Ltmp4:
@ CHECK: .long 65540
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,e,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp5:
@ CHECK: .long 65542
@ CHECK-LABEL: Ltmp6:
@ CHECK: .long 65543
@ CHECK: .end_data_region

@ Should not switch to section because it has no constant pool
@ CHECK-NOT: .section __TEXT,f,regular,pure_instructions

@ CHECK: .section __TEXT,g,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp7:
@ CHECK: .long foo
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,h,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp8:
@ CHECK: .long f5
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,i,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp9:
@ CHECK: .long f12
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,j,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp10:
@ CHECK: .long 257
@ CHECK-LABEL: Ltmp11:
@ CHECK: .long bar
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,k,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp12:
@ CHECK: .long 65544
@ CHECK-LABEL: Ltmp13:
@ CHECK: .long baz
@ CHECK: .end_data_region

@ CHECK: .section __TEXT,l,regular,pure_instructions
@ CHECK: .align 2
@ CHECK: .data_region
@ CHECK-LABEL: Ltmp14:
@ CHECK: .long 65545
@ CHECK-LABEL: Ltmp15:
@ CHECK: .long bar+4
@ CHECK: .end_data_region
@@ -0,0 +1,17 @@
@RUN: not llvm-mc -triple=armv7-unknown-linux-gnueabi -filetype=obj %s -o %t1 2> %t2
@RUN: cat %t2 | FileCheck %s
@RUN: not llvm-mc -triple=armv7-darwin-apple -filetype=obj %s -o %t1_darwin 2> %t2_darwin
@RUN: cat %t2_darwin | FileCheck %s

@These tests look for errors that should be reported for invalid object layout
@with the ldr pseudo. They are tested separately from parse errors because they
@only trigger when the file has successfully parsed and the object file is about
@to be written out.

.text
foo:
ldr r0, =0x101
.space 8000
@ CHECK: error: out of range pc-relative fixup value
@ CHECK: ldr r0, =0x101
@ CHECK: ^
Oops, something went wrong.

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