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[IR] Clean up dead instructions after simplifying a conditional branch

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Change BasicBlock::removePredecessor to optionally return a vector of
instructions which might be dead. Use this in ConstantFoldTerminator to
delete them if they are dead.

Reapply with a bug fix: don't drop the "!KeepOneInputPHIs" argument when
removePredecessor calls PHINode::removeIncomingValue.

Differential Revision: https://reviews.llvm.org/D80206
This commit is contained in:
Jay Foad 2020-05-18 19:12:29 +01:00
parent e4feed2398
commit 3e1ffcd6f3
4 changed files with 88 additions and 73 deletions
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9
include/llvm/IR/BasicBlock.h
View File

@ -22,6 +22,7 @@
#include "llvm/IR/Instruction.h"
#include "llvm/IR/SymbolTableListTraits.h"
#include "llvm/IR/Value.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/CBindingWrapping.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
@ -376,7 +377,13 @@ public:
/// If \p KeepOneInputPHIs is true then don't remove PHIs that are left with
/// zero or one incoming values, and don't simplify PHIs with all incoming
/// values the same.
void removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs = false);
///
/// If \p MaybeDeadInstrs is not nullptr then whenever we drop a reference to
/// an instruction, append it to the vector. The caller should check whether
/// these instructions are now trivially dead, and if so delete them.
void
removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs = false,
SmallVectorImpl<WeakTrackingVH> *MaybeDeadInstrs = nullptr);
bool canSplitPredecessors() const;

15
lib/IR/BasicBlock.cpp
View File

@ -323,8 +323,13 @@ iterator_range<BasicBlock::phi_iterator> BasicBlock::phis() {
/// If \p KeepOneInputPHIs is true then don't remove PHIs that are left with
/// zero or one incoming values, and don't simplify PHIs with all incoming
/// values the same.
void BasicBlock::removePredecessor(BasicBlock *Pred,
bool KeepOneInputPHIs) {
///
/// If \p MaybeDeadInstrs is not nullptr then whenever we drop a reference to
/// an instruction, append it to the vector. The caller should check whether
/// these instructions are now trivially dead, and if so delete them.
void BasicBlock::removePredecessor(
BasicBlock *Pred, bool KeepOneInputPHIs,
SmallVectorImpl<WeakTrackingVH> *MaybeDeadInstrs) {
// Use hasNUsesOrMore to bound the cost of this assertion for complex CFGs.
assert((hasNUsesOrMore(16) ||
find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
@ -338,7 +343,11 @@ void BasicBlock::removePredecessor(BasicBlock *Pred,
// Update all PHI nodes.
for (iterator II = begin(); isa<PHINode>(II);) {
PHINode *PN = cast<PHINode>(II++);
PN->removeIncomingValue(Pred, !KeepOneInputPHIs);
Value *V = PN->removeIncomingValue(Pred, !KeepOneInputPHIs);
if (MaybeDeadInstrs) {
if (auto *I = dyn_cast<Instruction>(V))
MaybeDeadInstrs->push_back(I);
}
if (!KeepOneInputPHIs) {
// If we have a single predecessor, removeIncomingValue erased the PHI
// node itself.

11
lib/Transforms/Utils/Local.cpp
View File

@ -126,8 +126,11 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
// Let the basic block know that we are letting go of it. Based on this,
// it will adjust it's PHI nodes.
OldDest->removePredecessor(BB);
// it will adjust its PHI nodes.
SmallVector<WeakTrackingVH, 8> MaybeDeadInstrs;
OldDest->removePredecessor(BB, false, &MaybeDeadInstrs);
RecursivelyDeleteTriviallyDeadInstructionsPermissive(MaybeDeadInstrs,
TLI);
// Replace the conditional branch with an unconditional one.
Builder.CreateBr(Destination);
@ -470,8 +473,8 @@ bool llvm::RecursivelyDeleteTriviallyDeadInstructionsPermissive(
MemorySSAUpdater *MSSAU) {
unsigned S = 0, E = DeadInsts.size(), Alive = 0;
for (; S != E; ++S) {
auto *I = cast<Instruction>(DeadInsts[S]);
if (!isInstructionTriviallyDead(I)) {
auto *I = dyn_cast<Instruction>(DeadInsts[S]);
if (!I || !isInstructionTriviallyDead(I)) {
DeadInsts[S] = nullptr;
++Alive;
}

126
test/Transforms/PGOProfile/chr.ll
View File

@ -448,34 +448,33 @@ define i32 @test_chr_5(i32* %i, i32 %sum0) !prof !14 {
; CHECK-NEXT: [[TMP0:%.*]] = load i32, i32* [[I:%.*]], align 4
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[TMP0]], 15
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq i32 [[TMP1]], 15
; CHECK-NEXT: br i1 [[TMP2]], label [[BB0:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb0:
; CHECK-NEXT: [[TMP3:%.*]] = add i32 [[SUM0:%.*]], 85
; CHECK-NEXT: [[TMP4:%.*]] = add i32 [[SUM0]], 173
; CHECK-NEXT: br i1 [[TMP2]], label [[BB1:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb1:
; CHECK-NEXT: [[TMP3:%.*]] = add i32 [[SUM0:%.*]], 173
; CHECK-NEXT: br label [[BB3:%.*]]
; CHECK: entry.split.nonchr:
; CHECK-NEXT: [[TMP5:%.*]] = and i32 [[TMP0]], 255
; CHECK-NEXT: [[TMP6:%.*]] = icmp eq i32 [[TMP5]], 0
; CHECK-NEXT: br i1 [[TMP6]], label [[BB3]], label [[BB0_NONCHR:%.*]], !prof !16
; CHECK-NEXT: [[TMP4:%.*]] = and i32 [[TMP0]], 255
; CHECK-NEXT: [[TMP5:%.*]] = icmp eq i32 [[TMP4]], 0
; CHECK-NEXT: br i1 [[TMP5]], label [[BB3]], label [[BB0_NONCHR:%.*]], !prof !16
; CHECK: bb0.nonchr:
; CHECK-NEXT: [[TMP7:%.*]] = and i32 [[TMP0]], 1
; CHECK-NEXT: [[TMP8:%.*]] = icmp eq i32 [[TMP7]], 0
; CHECK-NEXT: [[TMP9:%.*]] = add i32 [[SUM0]], 42
; CHECK-NEXT: [[SUM1_NONCHR:%.*]] = select i1 [[TMP8]], i32 [[SUM0]], i32 [[TMP9]], !prof !16
; CHECK-NEXT: [[TMP10:%.*]] = and i32 [[TMP0]], 2
; CHECK-NEXT: [[TMP11:%.*]] = icmp eq i32 [[TMP10]], 0
; CHECK-NEXT: [[TMP12:%.*]] = add i32 [[SUM1_NONCHR]], 43
; CHECK-NEXT: [[SUM2_NONCHR:%.*]] = select i1 [[TMP11]], i32 [[SUM1_NONCHR]], i32 [[TMP12]], !prof !16
; CHECK-NEXT: [[TMP13:%.*]] = and i32 [[TMP0]], 4
; CHECK-NEXT: [[TMP14:%.*]] = icmp eq i32 [[TMP13]], 0
; CHECK-NEXT: [[TMP15:%.*]] = and i32 [[TMP0]], 8
; CHECK-NEXT: [[TMP16:%.*]] = icmp eq i32 [[TMP15]], 0
; CHECK-NEXT: [[SUM4_NONCHR_V:%.*]] = select i1 [[TMP16]], i32 44, i32 88
; CHECK-NEXT: [[TMP6:%.*]] = and i32 [[TMP0]], 1
; CHECK-NEXT: [[TMP7:%.*]] = icmp eq i32 [[TMP6]], 0
; CHECK-NEXT: [[TMP8:%.*]] = add i32 [[SUM0]], 42
; CHECK-NEXT: [[SUM1_NONCHR:%.*]] = select i1 [[TMP7]], i32 [[SUM0]], i32 [[TMP8]], !prof !16
; CHECK-NEXT: [[TMP9:%.*]] = and i32 [[TMP0]], 2
; CHECK-NEXT: [[TMP10:%.*]] = icmp eq i32 [[TMP9]], 0
; CHECK-NEXT: [[TMP11:%.*]] = add i32 [[SUM1_NONCHR]], 43
; CHECK-NEXT: [[SUM2_NONCHR:%.*]] = select i1 [[TMP10]], i32 [[SUM1_NONCHR]], i32 [[TMP11]], !prof !16
; CHECK-NEXT: [[TMP12:%.*]] = and i32 [[TMP0]], 4
; CHECK-NEXT: [[TMP13:%.*]] = icmp eq i32 [[TMP12]], 0
; CHECK-NEXT: [[TMP14:%.*]] = and i32 [[TMP0]], 8
; CHECK-NEXT: [[TMP15:%.*]] = icmp eq i32 [[TMP14]], 0
; CHECK-NEXT: [[SUM4_NONCHR_V:%.*]] = select i1 [[TMP15]], i32 44, i32 88
; CHECK-NEXT: [[SUM4_NONCHR:%.*]] = add i32 [[SUM2_NONCHR]], [[SUM4_NONCHR_V]]
; CHECK-NEXT: [[SUM5_NONCHR:%.*]] = select i1 [[TMP14]], i32 [[SUM2_NONCHR]], i32 [[SUM4_NONCHR]], !prof !16
; CHECK-NEXT: [[SUM5_NONCHR:%.*]] = select i1 [[TMP13]], i32 [[SUM2_NONCHR]], i32 [[SUM4_NONCHR]], !prof !16
; CHECK-NEXT: br label [[BB3]]
; CHECK: bb3:
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[TMP4]], [[BB0]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[TMP3]], [[BB1]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: ret i32 [[SUM6]]
;
entry:
@ -548,34 +547,33 @@ define i32 @test_chr_5_1(i32* %i, i32 %sum0) !prof !14 {
; CHECK-NEXT: [[TMP3:%.*]] = and i32 [[TMP0]], 11
; CHECK-NEXT: [[TMP4:%.*]] = icmp eq i32 [[TMP3]], 11
; CHECK-NEXT: [[TMP5:%.*]] = and i1 [[TMP4]], [[TMP2]]
; CHECK-NEXT: br i1 [[TMP5]], label [[BB0:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb0:
; CHECK-NEXT: [[TMP6:%.*]] = add i32 [[SUM0]], 85
; CHECK-NEXT: [[TMP7:%.*]] = add i32 [[SUM0]], 173
; CHECK-NEXT: br i1 [[TMP5]], label [[BB1:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb1:
; CHECK-NEXT: [[TMP6:%.*]] = add i32 [[SUM0]], 173
; CHECK-NEXT: br label [[BB3:%.*]]
; CHECK: entry.split.nonchr:
; CHECK-NEXT: [[TMP8:%.*]] = and i32 [[TMP0]], 255
; CHECK-NEXT: [[TMP9:%.*]] = icmp eq i32 [[TMP8]], 0
; CHECK-NEXT: br i1 [[TMP9]], label [[BB3]], label [[BB0_NONCHR:%.*]], !prof !16
; CHECK-NEXT: [[TMP7:%.*]] = and i32 [[TMP0]], 255
; CHECK-NEXT: [[TMP8:%.*]] = icmp eq i32 [[TMP7]], 0
; CHECK-NEXT: br i1 [[TMP8]], label [[BB3]], label [[BB0_NONCHR:%.*]], !prof !16
; CHECK: bb0.nonchr:
; CHECK-NEXT: [[TMP10:%.*]] = and i32 [[TMP0]], 1
; CHECK-NEXT: [[TMP11:%.*]] = icmp eq i32 [[TMP10]], 0
; CHECK-NEXT: [[TMP12:%.*]] = add i32 [[SUM0]], 42
; CHECK-NEXT: [[SUM1_NONCHR:%.*]] = select i1 [[TMP11]], i32 [[SUM0]], i32 [[TMP12]], !prof !16
; CHECK-NEXT: [[TMP13:%.*]] = and i32 [[TMP0]], 2
; CHECK-NEXT: [[TMP14:%.*]] = icmp eq i32 [[TMP13]], 0
; CHECK-NEXT: [[TMP15:%.*]] = add i32 [[SUM1_NONCHR]], 43
; CHECK-NEXT: [[SUM2_NONCHR:%.*]] = select i1 [[TMP14]], i32 [[SUM1_NONCHR]], i32 [[TMP15]], !prof !16
; CHECK-NEXT: [[TMP16:%.*]] = and i32 [[SUM0]], 4
; CHECK-NEXT: [[TMP17:%.*]] = icmp eq i32 [[TMP16]], 0
; CHECK-NEXT: [[TMP18:%.*]] = and i32 [[TMP0]], 8
; CHECK-NEXT: [[TMP19:%.*]] = icmp eq i32 [[TMP18]], 0
; CHECK-NEXT: [[SUM4_NONCHR_V:%.*]] = select i1 [[TMP19]], i32 44, i32 88
; CHECK-NEXT: [[TMP9:%.*]] = and i32 [[TMP0]], 1
; CHECK-NEXT: [[TMP10:%.*]] = icmp eq i32 [[TMP9]], 0
; CHECK-NEXT: [[TMP11:%.*]] = add i32 [[SUM0]], 42
; CHECK-NEXT: [[SUM1_NONCHR:%.*]] = select i1 [[TMP10]], i32 [[SUM0]], i32 [[TMP11]], !prof !16
; CHECK-NEXT: [[TMP12:%.*]] = and i32 [[TMP0]], 2
; CHECK-NEXT: [[TMP13:%.*]] = icmp eq i32 [[TMP12]], 0
; CHECK-NEXT: [[TMP14:%.*]] = add i32 [[SUM1_NONCHR]], 43
; CHECK-NEXT: [[SUM2_NONCHR:%.*]] = select i1 [[TMP13]], i32 [[SUM1_NONCHR]], i32 [[TMP14]], !prof !16
; CHECK-NEXT: [[TMP15:%.*]] = and i32 [[SUM0]], 4
; CHECK-NEXT: [[TMP16:%.*]] = icmp eq i32 [[TMP15]], 0
; CHECK-NEXT: [[TMP17:%.*]] = and i32 [[TMP0]], 8
; CHECK-NEXT: [[TMP18:%.*]] = icmp eq i32 [[TMP17]], 0
; CHECK-NEXT: [[SUM4_NONCHR_V:%.*]] = select i1 [[TMP18]], i32 44, i32 88
; CHECK-NEXT: [[SUM4_NONCHR:%.*]] = add i32 [[SUM2_NONCHR]], [[SUM4_NONCHR_V]]
; CHECK-NEXT: [[SUM5_NONCHR:%.*]] = select i1 [[TMP17]], i32 [[SUM2_NONCHR]], i32 [[SUM4_NONCHR]], !prof !16
; CHECK-NEXT: [[SUM5_NONCHR:%.*]] = select i1 [[TMP16]], i32 [[SUM2_NONCHR]], i32 [[SUM4_NONCHR]], !prof !16
; CHECK-NEXT: br label [[BB3]]
; CHECK: bb3:
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[TMP7]], [[BB0]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[TMP6]], [[BB1]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: ret i32 [[SUM6]]
;
entry:
@ -649,10 +647,9 @@ define i32 @test_chr_6(i32* %i, i32* %j, i32 %sum0) !prof !14 {
; CHECK-NEXT: [[TMP0:%.*]] = and i32 [[I0]], 10
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i32 [[TMP0]], 10
; CHECK-NEXT: [[TMP2:%.*]] = and i1 [[TMP1]], [[V10]]
; CHECK-NEXT: br i1 [[TMP2]], label [[BB0:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb0:
; CHECK-NEXT: [[V8:%.*]] = add i32 [[SUM0:%.*]], 43
; CHECK-NEXT: [[V13:%.*]] = add i32 [[SUM0]], 131
; CHECK-NEXT: br i1 [[TMP2]], label [[BB1:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb1:
; CHECK-NEXT: [[V13:%.*]] = add i32 [[SUM0:%.*]], 131
; CHECK-NEXT: br label [[BB3:%.*]]
; CHECK: entry.split.nonchr:
; CHECK-NEXT: [[V1:%.*]] = and i32 [[I0]], 255
@ -672,7 +669,7 @@ define i32 @test_chr_6(i32* %i, i32* %j, i32 %sum0) !prof !14 {
; CHECK-NEXT: [[SUM5_NONCHR:%.*]] = select i1 [[V10_NONCHR]], i32 [[SUM2_NONCHR]], i32 [[SUM4_NONCHR]], !prof !16
; CHECK-NEXT: br label [[BB3]]
; CHECK: bb3:
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[V13]], [[BB0]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[V13]], [[BB1]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: ret i32 [[SUM6]]
;
entry:
@ -1737,28 +1734,27 @@ define i32 @test_chr_19(i32* %i, i32 %sum0) !prof !14 {
; CHECK-NEXT: [[TMP0:%.*]] = load i32, i32* [[I:%.*]], align 4
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[TMP0]], 9
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq i32 [[TMP1]], 9
; CHECK-NEXT: br i1 [[TMP2]], label [[BB0:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb0:
; CHECK-NEXT: [[TMP3:%.*]] = add i32 [[SUM0:%.*]], 85
; CHECK-NEXT: [[TMP4:%.*]] = add i32 [[SUM0]], 173
; CHECK-NEXT: br i1 [[TMP2]], label [[BB1:%.*]], label [[ENTRY_SPLIT_NONCHR:%.*]], !prof !15
; CHECK: bb1:
; CHECK-NEXT: [[TMP3:%.*]] = add i32 [[SUM0:%.*]], 173
; CHECK-NEXT: br label [[BB3:%.*]]
; CHECK: entry.split.nonchr:
; CHECK-NEXT: [[TMP5:%.*]] = and i32 [[TMP0]], 255
; CHECK-NEXT: [[TMP6:%.*]] = icmp eq i32 [[TMP5]], 0
; CHECK-NEXT: br i1 [[TMP6]], label [[BB3]], label [[BB0_NONCHR:%.*]], !prof !16
; CHECK-NEXT: [[TMP4:%.*]] = and i32 [[TMP0]], 255
; CHECK-NEXT: [[TMP5:%.*]] = icmp eq i32 [[TMP4]], 0
; CHECK-NEXT: br i1 [[TMP5]], label [[BB3]], label [[BB0_NONCHR:%.*]], !prof !16
; CHECK: bb0.nonchr:
; CHECK-NEXT: [[TMP7:%.*]] = and i32 [[TMP0]], 1
; CHECK-NEXT: [[TMP8:%.*]] = icmp eq i32 [[TMP7]], 0
; CHECK-NEXT: [[TMP9:%.*]] = add i32 [[SUM0]], 85
; CHECK-NEXT: [[SUM2_NONCHR:%.*]] = select i1 [[TMP8]], i32 [[SUM0]], i32 [[TMP9]], !prof !16
; CHECK-NEXT: [[TMP10:%.*]] = and i32 [[TMP0]], 8
; CHECK-NEXT: [[TMP11:%.*]] = icmp eq i32 [[TMP10]], 0
; CHECK-NEXT: [[SUM4_NONCHR_V:%.*]] = select i1 [[TMP11]], i32 44, i32 88
; CHECK-NEXT: [[TMP6:%.*]] = and i32 [[TMP0]], 1
; CHECK-NEXT: [[TMP7:%.*]] = icmp eq i32 [[TMP6]], 0
; CHECK-NEXT: [[TMP8:%.*]] = add i32 [[SUM0]], 85
; CHECK-NEXT: [[SUM2_NONCHR:%.*]] = select i1 [[TMP7]], i32 [[SUM0]], i32 [[TMP8]], !prof !16
; CHECK-NEXT: [[TMP9:%.*]] = and i32 [[TMP0]], 8
; CHECK-NEXT: [[TMP10:%.*]] = icmp eq i32 [[TMP9]], 0
; CHECK-NEXT: [[SUM4_NONCHR_V:%.*]] = select i1 [[TMP10]], i32 44, i32 88
; CHECK-NEXT: [[SUM4_NONCHR:%.*]] = add i32 [[SUM2_NONCHR]], [[SUM4_NONCHR_V]]
; CHECK-NEXT: [[SUM5_NONCHR:%.*]] = select i1 [[TMP8]], i32 [[SUM2_NONCHR]], i32 [[SUM4_NONCHR]], !prof !16
; CHECK-NEXT: [[SUM5_NONCHR:%.*]] = select i1 [[TMP7]], i32 [[SUM2_NONCHR]], i32 [[SUM4_NONCHR]], !prof !16
; CHECK-NEXT: br label [[BB3]]
; CHECK: bb3:
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[TMP4]], [[BB0]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: [[SUM6:%.*]] = phi i32 [ [[TMP3]], [[BB1]] ], [ [[SUM0]], [[ENTRY_SPLIT_NONCHR]] ], [ [[SUM5_NONCHR]], [[BB0_NONCHR]] ]
; CHECK-NEXT: ret i32 [[SUM6]]
;
entry: