[llvm] r257518 - Codegen: [PPC] Handle weighted comparisons when inserting selects.
Kyle Butt via llvm-commits
llvm-commits at lists.llvm.org
Fri Jan 15 10:32:49 PST 2016
Yes, an initializer would be best.
Sorry for the delay, gmail marked this as spam despite my instructions not
to.
I can do it if you'd prefer.
On Fri, Jan 15, 2016 at 8:26 AM, Aaron Ballman <aaron at aaronballman.com>
wrote:
> On Wed, Jan 13, 2016 at 11:34 AM, Benjamin Kramer <benny.kra at gmail.com>
> wrote:
> > On Wed, Jan 13, 2016 at 4:28 PM, Aaron Ballman via llvm-commits
> > <llvm-commits at lists.llvm.org> wrote:
> >> On Tue, Jan 12, 2016 at 4:00 PM, Kyle Butt via llvm-commits
> >> <llvm-commits at lists.llvm.org> wrote:
> >>> Author: iteratee
> >>> Date: Tue Jan 12 15:00:43 2016
> >>> New Revision: 257518
> >>>
> >>> URL: http://llvm.org/viewvc/llvm-project?rev=257518&view=rev
> >>> Log:
> >>> Codegen: [PPC] Handle weighted comparisons when inserting selects.
> >>>
> >>> Only non-weighted predicates were handled in
> PPCInstrInfo::insertSelect. Handle
> >>> the weighted predicates as well.
> >>>
> >>> This latent bug was triggered by r255398, because it added use of the
> >>> branch-weighted predicates.
> >>>
> >>> While here, switch over an enum instead of an int to get the compiler
> to enforce
> >>> totality in the future.
> >>>
> >>> Added:
> >>> llvm/trunk/test/CodeGen/PowerPC/2016-01-07-BranchWeightCrash.ll
> >>> Modified:
> >>> llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
> >>>
> >>> Modified: llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp
> >>> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp?rev=257518&r1=257517&r2=257518&view=diff
> >>>
> ==============================================================================
> >>> --- llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp (original)
> >>> +++ llvm/trunk/lib/Target/PowerPC/PPCInstrInfo.cpp Tue Jan 12 15:00:43
> 2016
> >>> @@ -744,20 +744,43 @@ void PPCInstrInfo::insertSelect(MachineB
> >>> "isel is for regular integer GPRs only");
> >>>
> >>> unsigned OpCode = Is64Bit ? PPC::ISEL8 : PPC::ISEL;
> >>> - unsigned SelectPred = Cond[0].getImm();
> >>> + auto SelectPred = static_cast<PPC::Predicate>(Cond[0].getImm());
> >>>
> >>> unsigned SubIdx;
> >>> bool SwapOps;
> >>> switch (SelectPred) {
> >>> - default: llvm_unreachable("invalid predicate for isel");
> >>> - case PPC::PRED_EQ: SubIdx = PPC::sub_eq; SwapOps = false; break;
> >>> - case PPC::PRED_NE: SubIdx = PPC::sub_eq; SwapOps = true; break;
> >>> - case PPC::PRED_LT: SubIdx = PPC::sub_lt; SwapOps = false; break;
> >>> - case PPC::PRED_GE: SubIdx = PPC::sub_lt; SwapOps = true; break;
> >>> - case PPC::PRED_GT: SubIdx = PPC::sub_gt; SwapOps = false; break;
> >>> - case PPC::PRED_LE: SubIdx = PPC::sub_gt; SwapOps = true; break;
> >>> - case PPC::PRED_UN: SubIdx = PPC::sub_un; SwapOps = false; break;
> >>> - case PPC::PRED_NU: SubIdx = PPC::sub_un; SwapOps = true; break;
> >>> + case PPC::PRED_EQ:
> >>> + case PPC::PRED_EQ_MINUS:
> >>> + case PPC::PRED_EQ_PLUS:
> >>> + SubIdx = PPC::sub_eq; SwapOps = false; break;
> >>> + case PPC::PRED_NE:
> >>> + case PPC::PRED_NE_MINUS:
> >>> + case PPC::PRED_NE_PLUS:
> >>> + SubIdx = PPC::sub_eq; SwapOps = true; break;
> >>> + case PPC::PRED_LT:
> >>> + case PPC::PRED_LT_MINUS:
> >>> + case PPC::PRED_LT_PLUS:
> >>> + SubIdx = PPC::sub_lt; SwapOps = false; break;
> >>> + case PPC::PRED_GE:
> >>> + case PPC::PRED_GE_MINUS:
> >>> + case PPC::PRED_GE_PLUS:
> >>> + SubIdx = PPC::sub_lt; SwapOps = true; break;
> >>> + case PPC::PRED_GT:
> >>> + case PPC::PRED_GT_MINUS:
> >>> + case PPC::PRED_GT_PLUS:
> >>> + SubIdx = PPC::sub_gt; SwapOps = false; break;
> >>> + case PPC::PRED_LE:
> >>> + case PPC::PRED_LE_MINUS:
> >>> + case PPC::PRED_LE_PLUS:
> >>> + SubIdx = PPC::sub_gt; SwapOps = true; break;
> >>> + case PPC::PRED_UN:
> >>> + case PPC::PRED_UN_MINUS:
> >>> + case PPC::PRED_UN_PLUS:
> >>> + SubIdx = PPC::sub_un; SwapOps = false; break;
> >>> + case PPC::PRED_NU:
> >>> + case PPC::PRED_NU_MINUS:
> >>> + case PPC::PRED_NU_PLUS:
> >>> + SubIdx = PPC::sub_un; SwapOps = true; break;
> >>> case PPC::PRED_BIT_SET: SubIdx = 0; SwapOps = false; break;
> >>> case PPC::PRED_BIT_UNSET: SubIdx = 0; SwapOps = true; break;
> >>> }
> >>
> >> One of our bots now diagnoses with:
> >>
> >> /opt/llvm/build-llvm/src/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp: In
> >> member function ‘virtual void
> >> llvm::PPCInstrInfo::insertSelect(llvm::MachineBasicBlock&,
> >> llvm::MachineBasicBlock::iterator, llvm::DebugLoc, unsigned int,
> >> llvm::ArrayRef<llvm::MachineOperand>, unsigned int, unsigned int)
> >> const’:
> >>
> /opt/llvm/build-llvm/src/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp:788:45:
> >> warning: ‘SwapOps’ may be used uninitialized in this function
> >> [-Wuninitialized]
> >>
> >> I think this is a false positive, but having the default:
> >> llvm_unreachable is likely not a terrible idea to silence the warning.
> >> I don't know enough about this code to feel comfortable adding it as a
> >> fix myself, however.
> >
> > Adding the default case back would defeat the warning for missing enum
> > values in the switch, if that was on from the beginning it would've
> > prevented this bug from ever creeping in. -Wcovered-switch-default
> > should also complain if we add a default here :)
>
> Good point.
>
> > It makes silencing the warning a bit harder. Choices I see are pulling
> > the switch into a separate function and using early returns +
> > llvm_unreachable or just adding an initializer to SwapOps to pacify
> > compilers that are missing covered switch smarts.
>
> If no one has a better idea, I will add an initializer to SwapOps later
> today.
>
> ~Aaron
>
> >
> > - Ben
> >
> >>
> >>>
> >>> Added: llvm/trunk/test/CodeGen/PowerPC/2016-01-07-BranchWeightCrash.ll
> >>> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/PowerPC/2016-01-07-BranchWeightCrash.ll?rev=257518&view=auto
> >>>
> ==============================================================================
> >>> --- llvm/trunk/test/CodeGen/PowerPC/2016-01-07-BranchWeightCrash.ll
> (added)
> >>> +++ llvm/trunk/test/CodeGen/PowerPC/2016-01-07-BranchWeightCrash.ll
> Tue Jan 12 15:00:43 2016
> >>> @@ -0,0 +1,35 @@
> >>> +; RUN: llc <%s | FileCheck %s
> >>> +target datalayout = "e-m:e-i64:64-n32:64"
> >>> +target triple = "powerpc64le-unknown-linux-gnu"
> >>> +
> >>> +%struct.buffer_t = type { i64, i8*, [4 x i32], [4 x i32], [4 x i32],
> i32, i8, i8, [2 x i8] }
> >>> +
> >>> +declare i32 @__f1(i8*, %struct.buffer_t* noalias)
> >>> +
> >>> +; CHECK-LABEL: f1:
> >>> +define i32 @f1(i8* %__user_context, %struct.buffer_t* noalias
> %f1.buffer) {
> >>> +entry:
> >>> + br i1 undef, label %"assert succeeded", label %"assert failed",
> !prof !1
> >>> +
> >>> +"assert failed": ; preds = %entry
> >>> + br label %destructor_block
> >>> +
> >>> +"assert succeeded": ; preds = %entry
> >>> + %__f1_result = call i32 @__f1(i8* %__user_context,
> %struct.buffer_t* %f1.buffer) #5
> >>> + %0 = icmp eq i32 %__f1_result, 0
> >>> + br i1 %0, label %"assert succeeded11", label %"assert failed10",
> !prof !1
> >>> +
> >>> +destructor_block: ; preds = %"assert
> succeeded11", %"assert failed10", %"assert failed"
> >>> + %1 = phi i32 [ undef, %"assert failed" ], [ %__f1_result, %"assert
> failed10" ], [ 0, %"assert succeeded11" ]
> >>> + ret i32 %1
> >>> +
> >>> +"assert failed10": ; preds = %"assert
> succeeded"
> >>> + br label %destructor_block
> >>> +
> >>> +"assert succeeded11": ; preds = %"assert
> succeeded"
> >>> + br label %destructor_block
> >>> +}
> >>> +
> >>> +attributes #5 = { nounwind }
> >>> +
> >>> +!1 = !{!"branch_weights", i32 1073741824, i32 0}
> >>>
> >>>
> >>> _______________________________________________
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> >>> llvm-commits at lists.llvm.org
> >>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
> >> _______________________________________________
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