[llvm] 8fffa40 - [GC] Remove redundant entiries in stackmap section (and test it this time)

Wed Mar 11 23:57:33 PDT 2020

Hi Philip,

clang warns on new code in this patch:

../lib/CodeGen/SelectionDAG/StatepointLowering.cpp:843:13: error:
unused variable 'BaseSD' [-Werror,-Wunused-variable]
    SDValue BaseSD = getValue(Relocate->getBasePtr());
            ^
1 error generated.

Can we just remove the line completely or is there some side effect in
getValue that is needed?

Regards,
Mikael

On Wed, 2020-03-11 at 21:24 -0700, Philip Reames via llvm-commits
wrote:
> Author: Philip Reames
> Date: 2020-03-11T21:24:48-07:00
> New Revision: 8fffa40400e8719222e7f67152c12738521fa9fb
> 
> URL: 
> https://protect2.fireeye.com/v1/url?k=3ded4adc-6167680a-3ded0a47-0cc47ad93dcc-77b6f9a7f7f52e82&q=1&e=b4cd1a3e-fe77-479c-a47b-f22079f5281f&u=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fcommit%2F8fffa40400e8719222e7f67152c12738521fa9fb
> DIFF: 
> https://protect2.fireeye.com/v1/url?k=c655e929-9adfcbff-c655a9b2-0cc47ad93dcc-8edef7b6eb27e30f&q=1&e=b4cd1a3e-fe77-479c-a47b-f22079f5281f&u=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fcommit%2F8fffa40400e8719222e7f67152c12738521fa9fb.diff
> 
> LOG: [GC] Remove redundant entiries in stackmap section (and test it
> this time)
> 
> This is a reimplementation of the optimization removed in D75964. The
> actual spill/fill optimization is handled by D76013, this one just
> worries about reducing the stackmap section size itself by
> eliminating redundant entries. As noted in the comments, we could go
> a lot further here, but avoiding the degenerate invoke case as we did
> before is probably "enough" in practice.
> 
> Differential Revision: 
> https://protect2.fireeye.com/v1/url?k=0b7c0ec1-57f62c17-0b7c4e5a-0cc47ad93dcc-9eb52bdd595d688c&q=1&e=b4cd1a3e-fe77-479c-a47b-f22079f5281f&u=https%3A%2F%2Freviews.llvm.org%2FD76021
> 
> Added: 
>     llvm/test/CodeGen/X86/statepoint-stackmap-size.ll
> 
> Modified: 
>     llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
> 
> Removed: 
>     
> 
> 
> #####################################################################
> ###########
> diff  --git a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
> b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
> index 40033db4e26d..e65b59416085 100644
> --- a/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
> +++ b/llvm/lib/CodeGen/SelectionDAG/StatepointLowering.cpp
> @@ -603,7 +603,7 @@ SDValue SelectionDAGBuilder::LowerAsSTATEPOINT(
>    // Clear state
>    StatepointLowering.startNewStatepoint(*this);
>    assert(SI.Bases.size() == SI.Ptrs.size() &&
> -         SI.Ptrs.size() == SI.GCRelocates.size());
> +         SI.Ptrs.size() <= SI.GCRelocates.size());
>  
>  #ifndef NDEBUG
>    for (auto *Reloc : SI.GCRelocates)
> @@ -823,10 +823,29 @@
> SelectionDAGBuilder::LowerStatepoint(ImmutableStatepoint ISP,
>                             ISP.getNumCallArgs(), ActualCallee,
>                             ISP.getActualReturnType(), false /*
> IsPatchPoint */);
>  
> +  // There may be duplication in the gc.relocate list; such as two
> copies of
> +  // each relocation on normal and exceptional path for an
> invoke.  We only
> +  // need to spill once and record one copy in the stackmap, but we
> need to
> +  // reload once per gc.relocate.  (Dedupping gc.relocates is
> trickier and best
> +  // handled as a CSE problem elsewhere.)
> +  // TODO: There a couple of major stackmap size optimizations we
> could do
> +  // here if we wished.
> +  // 1) If we've encountered a derived pair {B, D}, we don't need to
> actually
> +  // record {B,B} if it's seen later.
> +  // 2) Due to rematerialization, actual derived pointers are
> somewhat rare;
> +  // given that, we could change the format to record base pointer
> relocations
> +  // separately with half the space. This would require a format rev
> and a
> +  // fairly major rework of the STATEPOINT node though.
> +  SmallSet<SDValue, 8> Seen;
>    for (const GCRelocateInst *Relocate : ISP.getRelocates()) {
>      SI.GCRelocates.push_back(Relocate);
> -    SI.Bases.push_back(Relocate->getBasePtr());
> -    SI.Ptrs.push_back(Relocate->getDerivedPtr());
> +
> +    SDValue BaseSD = getValue(Relocate->getBasePtr());
> +    SDValue DerivedSD = getValue(Relocate->getDerivedPtr());
> +    if (Seen.insert(DerivedSD).second) {
> +      SI.Bases.push_back(Relocate->getBasePtr());
> +      SI.Ptrs.push_back(Relocate->getDerivedPtr());
> +    }
>    }
>  
>    SI.GCArgs = ArrayRef<const Use>(ISP.gc_args_begin(),
> ISP.gc_args_end());
> 
> diff  --git a/llvm/test/CodeGen/X86/statepoint-stackmap-size.ll
> b/llvm/test/CodeGen/X86/statepoint-stackmap-size.ll
> new file mode 100644
> index 000000000000..d4a8a04c644e
> --- /dev/null
> +++ b/llvm/test/CodeGen/X86/statepoint-stackmap-size.ll
> @@ -0,0 +1,22 @@
> +; RUN: llc  -verify-machineinstrs < %s | fgrep -A 10000
> .llvm_stackmaps | wc -l | FileCheck %s
> +
> +; Without removal of duplicate entries, the size is 62 lines
> +; CHECK: 50
> +
> +target triple = "x86_64-pc-linux-gnu"
> +
> +declare void @func()
> +
> +define i1 @test1(i32 addrspace(1)* %arg) gc "statepoint-example" {
> +entry:
> +  %safepoint_token = call token (i64, i32, void ()*, i32, i32, ...)
> @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()*
> @func, i32 0, i32 0, i32 0, i32 0, i32 addrspace(1)* %arg)
> +  %reloc1 = call i32 addrspace(1)*
> @llvm.experimental.gc.relocate.p1i32(token %safepoint_token,  i32 7,
> i32 7)
> +  %reloc2 = call i32 addrspace(1)*
> @llvm.experimental.gc.relocate.p1i32(token %safepoint_token,  i32 7,
> i32 7)
> +  %cmp1 = icmp eq i32 addrspace(1)* %reloc1, null
> +  %cmp2 = icmp eq i32 addrspace(1)* %reloc2, null
> +  %cmp = and i1 %cmp1, %cmp2
> +  ret i1 %cmp
> +}
> +
> +declare token @llvm.experimental.gc.statepoint.p0f_isVoidf(i64, i32,
> void ()*, i32, i32, ...)
> +declare i32 addrspace(1)*
> @llvm.experimental.gc.relocate.p1i32(token, i32, i32)
> 
> 
>         
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