Commit e0ea7cf2 authored by Tim Northover's avatar Tim Northover
Browse files

Merging r259228: 

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r259228 | tnorthover | 2016-01-29 11:18:46 -0800 (Fri, 29 Jan 2016) | 13 lines

ARM: don't mangle DAG constant if it has more than one use

The basic optimisation was to convert (mul $LHS, $complex_constant) into
roughly "(shl (mul $LHS, $simple_constant), $simple_amt)" when it was expected
to be cheaper. The original logic checks that the mul only has one use (since
we're mangling $complex_constant), but when used in even more complex
addressing modes there may be an outer addition that can pick up the wrong
value too.

I *think* the ARM addressing-mode problem is actually unreachable at the
moment, but that depends on complex assessments of the profitability of
pre-increment addressing modes so I've put a real check in there instead of an
assertion.
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llvm-svn: 259247
parent 99317a9d

llvm/lib/Target/ARM/ARMISelDAGToDAG.cpp

+2 −2
Original line number Diff line number Diff line
@@ -747,7 +747,7 @@ bool ARMDAGToDAGISel::SelectLdStSOReg(SDValue N, SDValue &Base, SDValue &Offset, 


  // If Offset is a multiply-by-constant and it's profitable to extract a shift

  // and use it in a shifted operand do so.

  if (Offset.getOpcode() == ISD::MUL) {

  if (Offset.getOpcode() == ISD::MUL && N.hasOneUse()) {

    unsigned PowerOfTwo = 0;

    SDValue NewMulConst;

    if (canExtractShiftFromMul(Offset, 31, PowerOfTwo, NewMulConst)) {
@@ -1422,7 +1422,7 @@ bool ARMDAGToDAGISel::SelectT2AddrModeSoReg(SDValue N, 


  // If OffReg is a multiply-by-constant and it's profitable to extract a shift

  // and use it in a shifted operand do so.

  if (OffReg.getOpcode() == ISD::MUL) {

  if (OffReg.getOpcode() == ISD::MUL && N.hasOneUse()) {

    unsigned PowerOfTwo = 0;

    SDValue NewMulConst;

    if (canExtractShiftFromMul(OffReg, 3, PowerOfTwo, NewMulConst)) {

llvm/test/CodeGen/ARM/shifter_operand.ll

+17 −0
Original line number Diff line number Diff line
@@ -239,3 +239,20 @@ define void @test_well_formed_dag(i32 %in1, i32 %in2, i32* %addr) { 
  store i32 %add, i32* %addr

  ret void

}



define { i32, i32 } @test_multi_use_add(i32 %base, i32 %offset) {

; CHECK-LABEL: test_multi_use_add:

; CHECK-THUMB: movs [[CONST:r[0-9]+]], #28

; CHECK-THUMB: movt [[CONST]], #1



  %prod = mul i32 %offset, 65564

  %sum = add i32 %base, %prod



  %ptr = inttoptr i32 %sum to i32*

  %loaded = load i32, i32* %ptr



  %ret.tmp = insertvalue { i32, i32 } undef, i32 %sum, 0

  %ret = insertvalue { i32, i32 } %ret.tmp, i32 %loaded, 1



  ret { i32, i32 } %ret

}