[llvm] r373477 - Reapply r373431 "Switch lowering: omit range check for bit tests when default is unreachable (PR43129)"
Hans Wennborg via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 2 07:35:07 PDT 2019
Author: hans
Date: Wed Oct 2 07:35:06 2019
New Revision: 373477
URL: http://llvm.org/viewvc/llvm-project?rev=373477&view=rev
Log:
Reapply r373431 "Switch lowering: omit range check for bit tests when default is unreachable (PR43129)"
This was reverted in r373454 due to breaking the expensive-checks bot.
This version addresses that by omitting the addSuccessorWithProb() call
when omitting the range check.
> Switch lowering: omit range check for bit tests when default is unreachable (PR43129)
>
> This is modeled after the same functionality for jump tables, which was
> added in r357067.
>
> Differential revision: https://reviews.llvm.org/D68131
Modified:
llvm/trunk/include/llvm/CodeGen/SwitchLoweringUtils.h
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
llvm/trunk/test/CodeGen/X86/switch-bt.ll
Modified: llvm/trunk/include/llvm/CodeGen/SwitchLoweringUtils.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/SwitchLoweringUtils.h?rev=373477&r1=373476&r2=373477&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/SwitchLoweringUtils.h (original)
+++ llvm/trunk/include/llvm/CodeGen/SwitchLoweringUtils.h Wed Oct 2 07:35:06 2019
@@ -212,13 +212,14 @@ struct BitTestBlock {
BitTestInfo Cases;
BranchProbability Prob;
BranchProbability DefaultProb;
+ bool OmitRangeCheck;
BitTestBlock(APInt F, APInt R, const Value *SV, unsigned Rg, MVT RgVT, bool E,
bool CR, MachineBasicBlock *P, MachineBasicBlock *D,
BitTestInfo C, BranchProbability Pr)
: First(std::move(F)), Range(std::move(R)), SValue(SV), Reg(Rg),
RegVT(RgVT), Emitted(E), ContiguousRange(CR), Parent(P), Default(D),
- Cases(std::move(C)), Prob(Pr) {}
+ Cases(std::move(C)), Prob(Pr), OmitRangeCheck(false) {}
};
/// Return the range of values within a range.
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=373477&r1=373476&r2=373477&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Wed Oct 2 07:35:06 2019
@@ -2622,17 +2622,11 @@ void SelectionDAGBuilder::visitBitTestHe
// Subtract the minimum value.
SDValue SwitchOp = getValue(B.SValue);
EVT VT = SwitchOp.getValueType();
- SDValue Sub = DAG.getNode(ISD::SUB, dl, VT, SwitchOp,
- DAG.getConstant(B.First, dl, VT));
-
- // Check range.
- const TargetLowering &TLI = DAG.getTargetLoweringInfo();
- SDValue RangeCmp = DAG.getSetCC(
- dl, TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(),
- Sub.getValueType()),
- Sub, DAG.getConstant(B.Range, dl, VT), ISD::SETUGT);
+ SDValue RangeSub =
+ DAG.getNode(ISD::SUB, dl, VT, SwitchOp, DAG.getConstant(B.First, dl, VT));
// Determine the type of the test operands.
+ const TargetLowering &TLI = DAG.getTargetLoweringInfo();
bool UsePtrType = false;
if (!TLI.isTypeLegal(VT)) {
UsePtrType = true;
@@ -2645,6 +2639,7 @@ void SelectionDAGBuilder::visitBitTestHe
break;
}
}
+ SDValue Sub = RangeSub;
if (UsePtrType) {
VT = TLI.getPointerTy(DAG.getDataLayout());
Sub = DAG.getZExtOrTrunc(Sub, dl, VT);
@@ -2656,20 +2651,29 @@ void SelectionDAGBuilder::visitBitTestHe
MachineBasicBlock* MBB = B.Cases[0].ThisBB;
- addSuccessorWithProb(SwitchBB, B.Default, B.DefaultProb);
+ if (!B.OmitRangeCheck)
+ addSuccessorWithProb(SwitchBB, B.Default, B.DefaultProb);
addSuccessorWithProb(SwitchBB, MBB, B.Prob);
SwitchBB->normalizeSuccProbs();
- SDValue BrRange = DAG.getNode(ISD::BRCOND, dl,
- MVT::Other, CopyTo, RangeCmp,
- DAG.getBasicBlock(B.Default));
+ SDValue Root = CopyTo;
+ if (!B.OmitRangeCheck) {
+ // Conditional branch to the default block.
+ SDValue RangeCmp = DAG.getSetCC(dl,
+ TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(),
+ RangeSub.getValueType()),
+ RangeSub, DAG.getConstant(B.Range, dl, RangeSub.getValueType()),
+ ISD::SETUGT);
+
+ Root = DAG.getNode(ISD::BRCOND, dl, MVT::Other, Root, RangeCmp,
+ DAG.getBasicBlock(B.Default));
+ }
// Avoid emitting unnecessary branches to the next block.
if (MBB != NextBlock(SwitchBB))
- BrRange = DAG.getNode(ISD::BR, dl, MVT::Other, BrRange,
- DAG.getBasicBlock(MBB));
+ Root = DAG.getNode(ISD::BR, dl, MVT::Other, Root, DAG.getBasicBlock(MBB));
- DAG.setRoot(BrRange);
+ DAG.setRoot(Root);
}
/// visitBitTestCase - this function produces one "bit test"
@@ -10164,8 +10168,6 @@ void SelectionDAGBuilder::lowerWorkItem(
break;
}
case CC_BitTests: {
- // FIXME: If Fallthrough is unreachable, skip the range check.
-
// FIXME: Optimize away range check based on pivot comparisons.
BitTestBlock *BTB = &SL->BitTestCases[I->BTCasesIndex];
@@ -10186,6 +10188,11 @@ void SelectionDAGBuilder::lowerWorkItem(
BTB->DefaultProb -= DefaultProb / 2;
}
+ if (FallthroughUnreachable) {
+ // Skip the range check if the fallthrough block is unreachable.
+ BTB->OmitRangeCheck = true;
+ }
+
// If we're in the right place, emit the bit test header right now.
if (CurMBB == SwitchMBB) {
visitBitTestHeader(*BTB, SwitchMBB);
Modified: llvm/trunk/test/CodeGen/X86/switch-bt.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/switch-bt.ll?rev=373477&r1=373476&r2=373477&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/switch-bt.ll (original)
+++ llvm/trunk/test/CodeGen/X86/switch-bt.ll Wed Oct 2 07:35:06 2019
@@ -157,13 +157,12 @@ sw.epilog:
}
-; TODO: Omit the range check when the default case is unreachable, see PR43129.
+; Omit the range check when the default case is unreachable, see PR43129.
declare void @g(i32)
define void @test5(i32 %x) {
; CHECK-LABEL: test5
-; CHECK: cmpl $8, %edi
-; CHECK: ja
+; CHECK-NOT: cmp
; 73 = 2^0 + 2^3 + 2^6
; CHECK: movl $73
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