[llvm-commits] [llvm] r169796 - in /llvm/trunk: include/llvm/CodeGen/FastISel.h lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp lib/Target/ARM/ARMFastISel.cpp lib/Target/X86/X86FastISel.cpp test/CodeGen/X86/tailcall-fastisel.ll
Eli Friedman
eli.friedman at gmail.com
Mon Dec 10 16:38:50 PST 2012
On Mon, Dec 10, 2012 at 4:18 PM, Chad Rosier <mcrosier at apple.com> wrote:
> Author: mcrosier
> Date: Mon Dec 10 18:18:02 2012
> New Revision: 169796
>
> URL: http://llvm.org/viewvc/llvm-project?rev=169796&view=rev
> Log:
> Fall back to the selection dag isel to select tail calls.
>
> This shouldn't affect codegen for -O0 compiles as tail call markers are not
> emitted in unoptimized compiles. Testing with the external/internal nightly
> test suite reveals no change in compile time performance. Testing with -O1,
> -O2 and -O3 with fast-isel enabled did not cause any compile-time or
> execution-time failures. All tests were performed on my x86 machine.
> I'll monitor our arm testers to ensure no regressions occur there.
>
> In an upcoming clang patch I will be marking the objc_autoreleaseReturnValue
> and objc_retainAutoreleaseReturnValue as tail calls unconditionally. While
> it's theoretically true that this is just an optimization, it's an
> optimization that we very much want to happen even at -O0, or else ARC
> applications become substantially harder to debug.
>
> Part of rdar://12553082
>
> Modified:
> llvm/trunk/include/llvm/CodeGen/FastISel.h
> llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
> llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
> llvm/trunk/lib/Target/ARM/ARMFastISel.cpp
> llvm/trunk/lib/Target/X86/X86FastISel.cpp
> llvm/trunk/test/CodeGen/X86/tailcall-fastisel.ll
>
> Modified: llvm/trunk/include/llvm/CodeGen/FastISel.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/FastISel.h?rev=169796&r1=169795&r2=169796&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/CodeGen/FastISel.h (original)
> +++ llvm/trunk/include/llvm/CodeGen/FastISel.h Mon Dec 10 18:18:02 2012
> @@ -131,6 +131,10 @@
> /// into the current block.
> void recomputeInsertPt();
>
> + /// removeDeadCode - Remove all dead instructions between the I and E.
> + void removeDeadCode(MachineBasicBlock::iterator I,
> + MachineBasicBlock::iterator E);
> +
> struct SavePoint {
> MachineBasicBlock::iterator InsertPt;
> DebugLoc DL;
> @@ -395,10 +399,6 @@
>
> /// hasTrivialKill - Test whether the given value has exactly one use.
> bool hasTrivialKill(const Value *V) const;
> -
> - /// removeDeadCode - Remove all dead instructions between the I and E.
> - void removeDeadCode(MachineBasicBlock::iterator I,
> - MachineBasicBlock::iterator E);
> };
>
> }
>
> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=169796&r1=169795&r2=169796&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
> +++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Mon Dec 10 18:18:02 2012
> @@ -5273,11 +5273,6 @@
> !isInTailCallPosition(CS, CS.getAttributes().getRetAttributes(), TLI))
> isTailCall = false;
>
> - // If there's a possibility that fast-isel has already selected some amount
> - // of the current basic block, don't emit a tail call.
> - if (isTailCall && TM.Options.EnableFastISel)
> - isTailCall = false;
> -
> TargetLowering::
> CallLoweringInfo CLI(getRoot(), RetTy, FTy, isTailCall, Callee, Args, DAG,
> getCurDebugLoc(), CS);
>
> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp?rev=169796&r1=169795&r2=169796&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp (original)
> +++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp Mon Dec 10 18:18:02 2012
> @@ -1113,19 +1113,21 @@
> }
>
> bool HadTailCall = false;
> + MachineBasicBlock::iterator SavedInsertPt = FuncInfo->InsertPt;
> SelectBasicBlock(Inst, BI, HadTailCall);
>
> - // Recompute NumFastIselRemaining as Selection DAG instruction
> - // selection may have handled the call, input args, etc.
> - unsigned RemainingNow = std::distance(Begin, BI);
> - NumFastIselFailures += NumFastIselRemaining - RemainingNow;
> -
> // If the call was emitted as a tail call, we're done with the block.
> + // We also need to delete any previously emitted instructions.
> if (HadTailCall) {
> + FastIS->removeDeadCode(SavedInsertPt, FuncInfo->MBB->end());
> --BI;
> break;
> }
>
> + // Recompute NumFastIselRemaining as Selection DAG instruction
> + // selection may have handled the call, input args, etc.
> + unsigned RemainingNow = std::distance(Begin, BI);
> + NumFastIselFailures += NumFastIselRemaining - RemainingNow;
> NumFastIselRemaining = RemainingNow;
> continue;
> }
>
> Modified: llvm/trunk/lib/Target/ARM/ARMFastISel.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMFastISel.cpp?rev=169796&r1=169795&r2=169796&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/ARM/ARMFastISel.cpp (original)
> +++ llvm/trunk/lib/Target/ARM/ARMFastISel.cpp Mon Dec 10 18:18:02 2012
> @@ -2284,6 +2284,9 @@
> // Can't handle inline asm.
> if (isa<InlineAsm>(Callee)) return false;
>
> + // Allow SelectionDAG isel to handle tail calls.
> + if (CI->isTailCall()) return false;
I'll just note that "isTailCall" doesn't precisely match the meaning
of "tail call" you want; it just means "that the callee function does
not access any allocas or varargs in the caller"
(http://llvm.org/docs/LangRef.html#call-instruction). I mean, this
will probably work in practice, but you're abusing the semantics a
bit.
-Eli
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