[llvm] r177338 - Fix PPC unaligned 64-bit loads and stores

Hal Finkel hfinkel at anl.gov
Tue Mar 19 01:26:11 PDT 2013


----- Original Message -----
> From: "Hal Finkel" <hfinkel at anl.gov>
> To: llvm-commits at cs.uiuc.edu
> Sent: Monday, March 18, 2013 6:00:58 PM
> Subject: [llvm] r177338 - Fix PPC unaligned 64-bit loads and stores
> 
> Author: hfinkel
> Date: Mon Mar 18 18:00:58 2013
> New Revision: 177338
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=177338&view=rev
> Log:
> Fix PPC unaligned 64-bit loads and stores
> 
> PPC64 supports unaligned loads and stores of 64-bit values, but
> in order to use the r+i forms, the offset must be a multiple of 4.
> Unfortunately, this cannot always be determined by examining the
> immediate itself because it might be available only via a TOC entry.

I forgot to add that the credit for diagnosing the problem goes to Bill Schmidt. This was non-trivial because the bug was only observable as a linker error message like this:
/usr/bin/ld: Output/ldecod.llvm.o: error: relocation R_PPC64_TOC16_LO_DS not a multiple of 4

 -Hal

> 
> In order to get around this issue, we additionally predicate the
> selection of the r+i form on the alignment of the load or store
> (forcing it to be at least 4 in order to select the r+i form).
> 
> Added:
>     llvm/trunk/test/CodeGen/PowerPC/unal4-std.ll
> Modified:
>     llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp
>     llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td
>     llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td
> 
> Modified: llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp?rev=177338&r1=177337&r2=177338&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp (original)
> +++ llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp Mon Mar 18
> 18:00:58 2013
> @@ -1183,13 +1183,15 @@ bool PPCTargetLowering::getPreIndexedAdd
>  
>    SDValue Ptr;
>    EVT VT;
> +  unsigned Alignment;
>    if (LoadSDNode *LD = dyn_cast<LoadSDNode>(N)) {
>      Ptr = LD->getBasePtr();
>      VT = LD->getMemoryVT();
> -
> +    Alignment = LD->getAlignment();
>    } else if (StoreSDNode *ST = dyn_cast<StoreSDNode>(N)) {
>      Ptr = ST->getBasePtr();
>      VT  = ST->getMemoryVT();
> +    Alignment = ST->getAlignment();
>    } else
>      return false;
>  
> @@ -1208,6 +1210,10 @@ bool PPCTargetLowering::getPreIndexedAdd
>      if (!SelectAddressRegImm(Ptr, Offset, Base, DAG))
>        return false;
>    } else {
> +    // LDU/STU need an address with at least 4-byte alignment.
> +    if (Alignment < 4)
> +      return false;
> +
>      // reg + imm * 4.
>      if (!SelectAddressRegImmShift(Ptr, Offset, Base, DAG))
>        return false;
> 
> Modified: llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td?rev=177338&r1=177337&r2=177338&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td (original)
> +++ llvm/trunk/lib/Target/PowerPC/PPCInstr64Bit.td Mon Mar 18
> 18:00:58 2013
> @@ -555,7 +555,8 @@ def LHA8: DForm_1<42, (outs G8RC:$rD), (
>                    PPC970_DGroup_Cracked;
>  def LWA  : DSForm_1<58, 2, (outs G8RC:$rD), (ins memrix:$src),
>                      "lwa $rD, $src", LdStLWA,
> -                    [(set G8RC:$rD, (sextloadi32 ixaddr:$src))]>,
> isPPC64,
> +                    [(set G8RC:$rD,
> +                          (aligned4sextloadi32 ixaddr:$src))]>,
> isPPC64,
>                      PPC970_DGroup_Cracked;
>  def LHAX8: XForm_1<31, 343, (outs G8RC:$rD), (ins memrr:$src),
>                     "lhax $rD, $src", LdStLHA,
> @@ -648,7 +649,7 @@ def LWZUX8 : XForm_1<31, 55, (outs G8RC:
>  let canFoldAsLoad = 1, PPC970_Unit = 2 in {
>  def LD   : DSForm_1<58, 0, (outs G8RC:$rD), (ins memrix:$src),
>                      "ld $rD, $src", LdStLD,
> -                    [(set G8RC:$rD, (load ixaddr:$src))]>, isPPC64;
> +                    [(set G8RC:$rD, (aligned4load ixaddr:$src))]>,
> isPPC64;
>  def LDrs : DSForm_1<58, 0, (outs G8RC:$rD), (ins memrs:$src),
>                      "ld $rD, $src", LdStLD,
>                      []>, isPPC64;
> @@ -682,6 +683,10 @@ def LDtoc_restore : DSForm_1a<58, 0, (ou
>  def LDX  : XForm_1<31,  21, (outs G8RC:$rD), (ins memrr:$src),
>                     "ldx $rD, $src", LdStLD,
>                     [(set G8RC:$rD, (load xaddr:$src))]>, isPPC64;
> +let isCodeGenOnly = 1 in
> +def LDXu  : XForm_1<31,  21, (outs G8RC:$rD), (ins memrr:$src),
> +                    "ldx $rD, $src", LdStLD,
> +                    [(set G8RC:$rD, (load xaddr:$src))]>, isPPC64;
>                     
>  let mayLoad = 1 in
>  def LDU  : DSForm_1<58, 1, (outs G8RC:$rD, ptr_rc:$ea_result), (ins
>  memrix:$addr),
> @@ -798,7 +803,7 @@ def STWX8 : XForm_8<31, 151, (outs), (in
>  // Normal 8-byte stores.
>  def STD  : DSForm_1<62, 0, (outs), (ins G8RC:$rS, memrix:$dst),
>                      "std $rS, $dst", LdStSTD,
> -                    [(store G8RC:$rS, ixaddr:$dst)]>, isPPC64;
> +                    [(aligned4store G8RC:$rS, ixaddr:$dst)]>,
> isPPC64;
>  def STDX  : XForm_8<31, 149, (outs), (ins G8RC:$rS, memrr:$dst),
>                     "stdx $rS, $dst", LdStSTD,
>                     [(store G8RC:$rS, xaddr:$dst)]>, isPPC64,
> @@ -833,8 +838,9 @@ def STWU8 : DForm_1a<37, (outs ptr_rc:$e
>  def STDU : DSForm_1a<62, 1, (outs ptr_rc:$ea_res), (ins G8RC:$rS,
>                                          s16immX4:$ptroff,
>                                          ptr_rc:$ptrreg),
>                      "stdu $rS, $ptroff($ptrreg)", LdStSTDU,
> -                    [(set ptr_rc:$ea_res, (pre_store G8RC:$rS,
> ptr_rc:$ptrreg,
> -
>                                                     iaddroff:$ptroff))]>,
> +                    [(set ptr_rc:$ea_res,
> +                       (aligned4pre_store G8RC:$rS, ptr_rc:$ptrreg,
> +                                          iaddroff:$ptroff))]>,
>                      RegConstraint<"$ptrreg = $ea_res">,
>                      NoEncode<"$ea_res">,
>                      isPPC64;
>  
> @@ -979,3 +985,13 @@ def : Pat<(add G8RC:$in, (PPChi tjumptab
>            (ADDIS8 G8RC:$in, tjumptable:$g)>;
>  def : Pat<(add G8RC:$in, (PPChi tblockaddress:$g, 0)),
>            (ADDIS8 G8RC:$in, tblockaddress:$g)>;
> +
> +// Patterns to match r+r indexed loads and stores for
> +// addresses without at least 4-byte alignment.
> +def : Pat<(i64 (unaligned4sextloadi32 xoaddr:$src)),
> +          (LWAX xoaddr:$src)>;
> +def : Pat<(i64 (unaligned4load xoaddr:$src)),
> +          (LDX xoaddr:$src)>;
> +def : Pat<(unaligned4store G8RC:$rS, xoaddr:$dst),
> +          (STDX G8RC:$rS, xoaddr:$dst)>;
> +
> 
> Modified: llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td?rev=177338&r1=177337&r2=177338&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td (original)
> +++ llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.td Mon Mar 18 18:00:58
> 2013
> @@ -278,6 +278,38 @@ def imm16ShiftedSExt : PatLeaf<(imm), [{
>    return N->getZExtValue() == (uint64_t)(int)N->getZExtValue();
>  }], HI16>;
>  
> +// Some r+i load/store instructions (such as LD, STD, LDU, etc.)
> that require
> +// restricted memrix (offset/4) constants are alignment sensitive.
> If these
> +// offsets are hidden behind TOC entries than the values of the
> lower-order
> +// bits cannot be checked directly. As a result, we need to also
> incorporate
> +// an alignment check into the relevant patterns.
> +
> +def aligned4load : PatFrag<(ops node:$ptr), (load node:$ptr), [{
> +  return cast<LoadSDNode>(N)->getAlignment() >= 4;
> +}]>;
> +def aligned4store : PatFrag<(ops node:$val, node:$ptr),
> +                            (store node:$val, node:$ptr), [{
> +  return cast<StoreSDNode>(N)->getAlignment() >= 4;
> +}]>;
> +def aligned4sextloadi32 : PatFrag<(ops node:$ptr), (sextloadi32
> node:$ptr), [{
> +  return cast<LoadSDNode>(N)->getAlignment() >= 4;
> +}]>;
> +def aligned4pre_store : PatFrag<
> +                          (ops node:$val, node:$base, node:$offset),
> +                          (pre_store node:$val, node:$base,
> node:$offset), [{
> +  return cast<StoreSDNode>(N)->getAlignment() >= 4;
> +}]>;
> +
> +def unaligned4load : PatFrag<(ops node:$ptr), (load node:$ptr), [{
> +  return cast<LoadSDNode>(N)->getAlignment() < 4;
> +}]>;
> +def unaligned4store : PatFrag<(ops node:$val, node:$ptr),
> +                              (store node:$val, node:$ptr), [{
> +  return cast<StoreSDNode>(N)->getAlignment() < 4;
> +}]>;
> +def unaligned4sextloadi32 : PatFrag<(ops node:$ptr), (sextloadi32
> node:$ptr), [{
> +  return cast<LoadSDNode>(N)->getAlignment() < 4;
> +}]>;
>  
>  //===----------------------------------------------------------------------===//
>  // PowerPC Flag Definitions.
> 
> Added: llvm/trunk/test/CodeGen/PowerPC/unal4-std.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/PowerPC/unal4-std.ll?rev=177338&view=auto
> ==============================================================================
> --- llvm/trunk/test/CodeGen/PowerPC/unal4-std.ll (added)
> +++ llvm/trunk/test/CodeGen/PowerPC/unal4-std.ll Mon Mar 18 18:00:58
> 2013
> @@ -0,0 +1,24 @@
> +; RUN: llc < %s -mcpu=pwr7 | FileCheck %s
> +target datalayout =
> "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
> +target triple = "powerpc64-unknown-linux-gnu"
> +
> +define fastcc void @copy_to_conceal() #0 {
> +entry:
> +  br i1 undef, label %if.then, label %if.end210
> +
> +if.then:                                          ; preds = %entry
> +  br label %vector.body.i
> +
> +vector.body.i:                                    ; preds =
> %vector.body.i, %if.then
> +  %index.i = phi i64 [ 0, %vector.body.i ], [ 0, %if.then ]
> +  store <8 x i16> zeroinitializer, <8 x i16>* undef, align 2
> +  br label %vector.body.i
> +
> +if.end210:                                        ; preds = %entry
> +  ret void
> +
> +; CHECK: @copy_to_conceal
> +; CHECK: stdx {{[0-9]+}}, 0,
> +}
> +
> +attributes #0 = { nounwind "less-precise-fpmad"="false"
> "no-frame-pointer-elim"="false"
> "no-frame-pointer-elim-non-leaf"="true" "no-infs-fp-math"="false"
> "no-nans-fp-math"="false" "unsafe-fp-math"="false"
> "use-soft-float"="false" }
> 
> 
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