[llvm] r302416 - [ARM] Clear the constant pool cache on explicit .ltorg directives

[James Molloy via llvm-commits]

Hi Martin,

Apologies, I have reverted this in r303536. I had to revert the
underlying r286006, which is what your patch was fixing. r286006 caused
PR32825 which wasn't addressed.

Cheers,

James

On Mon, 8 May 2017 at 11:39 Martin Storsjo via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: mstorsjo
> Date: Mon May  8 05:26:24 2017
> New Revision: 302416
>
> URL: http://llvm.org/viewvc/llvm-project?rev=302416&view=rev
> Log:
> [ARM] Clear the constant pool cache on explicit .ltorg directives
>
> Multiple ldr pseudoinstructions with the same constant value will
> reuse the same constant pool entry. However, if the constant pool
> is explicitly flushed with a .ltorg directive, we should not try
> to reference constants in the previous pool any longer, since they
> may be out of range.
>
> This fixes assembling hand-written assembler source which repeatedly
> loads the same constant value, across a binary size larger than the
> pc-relative fixup range for ldr instructions (4096 bytes). Such
> assembler source already uses explicit .ltorg instructions to emit
> constant pools with regular intervals. However if we try to reuse
> constants emitted in earlier pools, they end up out of range.
>
> This makes the output of the testcase match what binutils gas does
> (prior to this patch, it would fail to assemble).
>
> Differential Revision: https://reviews.llvm.org/D32847
>
> Added:
>     llvm/trunk/test/MC/ARM/ltorg-range.s
> Modified:
>     llvm/trunk/include/llvm/MC/ConstantPools.h
>     llvm/trunk/lib/MC/ConstantPools.cpp
>     llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp
>
> Modified: llvm/trunk/include/llvm/MC/ConstantPools.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/ConstantPools.h?rev=302416&r1=302415&r2=302416&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/MC/ConstantPools.h (original)
> +++ llvm/trunk/include/llvm/MC/ConstantPools.h Mon May  8 05:26:24 2017
> @@ -63,6 +63,8 @@ public:
>
>    // Return true if the constant pool is empty
>    bool empty();
> +
> +  void clearCache();
>  };
>
>  class AssemblerConstantPools {
> @@ -86,6 +88,7 @@ class AssemblerConstantPools {
>  public:
>    void emitAll(MCStreamer &Streamer);
>    void emitForCurrentSection(MCStreamer &Streamer);
> +  void clearCacheForCurrentSection(MCStreamer &Streamer);
>    const MCExpr *addEntry(MCStreamer &Streamer, const MCExpr *Expr,
>                           unsigned Size, SMLoc Loc);
>
>
> Modified: llvm/trunk/lib/MC/ConstantPools.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/ConstantPools.cpp?rev=302416&r1=302415&r2=302416&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/MC/ConstantPools.cpp (original)
> +++ llvm/trunk/lib/MC/ConstantPools.cpp Mon May  8 05:26:24 2017
> @@ -57,6 +57,10 @@ const MCExpr *ConstantPool::addEntry(con
>
>  bool ConstantPool::empty() { return Entries.empty(); }
>
> +void ConstantPool::clearCache() {
> +  CachedEntries.clear();
> +}
> +
>  //
>  // AssemblerConstantPools implementation
>  //
> @@ -98,6 +102,13 @@ void AssemblerConstantPools::emitForCurr
>    }
>  }
>
> +void AssemblerConstantPools::clearCacheForCurrentSection(MCStreamer
> &Streamer) {
> +  MCSection *Section = Streamer.getCurrentSectionOnly();
> +  if (ConstantPool *CP = getConstantPool(Section)) {
> +    CP->clearCache();
> +  }
> +}
> +
>  const MCExpr *AssemblerConstantPools::addEntry(MCStreamer &Streamer,
>                                                 const MCExpr *Expr,
>                                                 unsigned Size, SMLoc Loc) {
>
> Modified: llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp?rev=302416&r1=302415&r2=302416&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp (original)
> +++ llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMTargetStreamer.cpp Mon May
> 8 05:26:24 2017
> @@ -38,6 +38,7 @@ const MCExpr *ARMTargetStreamer::addCons
>
>  void ARMTargetStreamer::emitCurrentConstantPool() {
>    ConstantPools->emitForCurrentSection(Streamer);
> +  ConstantPools->clearCacheForCurrentSection(Streamer);
>  }
>
>  // finish() - write out any non-empty assembler constant pools.
>
> Added: llvm/trunk/test/MC/ARM/ltorg-range.s
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ARM/ltorg-range.s?rev=302416&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/MC/ARM/ltorg-range.s (added)
> +++ llvm/trunk/test/MC/ARM/ltorg-range.s Mon May  8 05:26:24 2017
> @@ -0,0 +1,27 @@
> +@ RUN: llvm-mc -triple armv7-unknown-linux-gnueabi -filetype obj -o - %s \
> +@ RUN:   | llvm-objdump -d - | FileCheck %s
> +
> +        ldr r0, =0x01020304
> +@ CHECK: ldr
> +        .ltorg
> +@ CHECK: 0x01020304
> +        ldr r0, =0x01020304
> +        ldr r0, =0x01020304
> +        ldr r0, =0x01020304
> +@ CHECK: ldr
> +@ CHECK: ldr
> +@ CHECK: ldr
> +        .ltorg
> +@ CHECK: 0x01020304
> +    .rep 1028
> +        .word 0
> +    .endr
> +@ CHECK: 0x00000000
> +
> +        ldr r0, =0x01020304
> +@ CHECK: ldr
> +        .ltorg
> +@ CHECK: 0x01020304
> +    .rep 1028
> +        .word 0
> +    .endr
>
>
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