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[SimplifyCFG] Add support for sinking instructions with multiple uses #95521

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merged 2 commits into from
Jun 17, 2024
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[SimplifyCFG] Add support for sinking instructions with multiple uses #95521

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[SimplifyCFG] Add support for sinking instructions with multiple uses
nikic Jun 4, 2024
d92d3e8
comment fixes
nikic Jun 14, 2024
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25 changes: 11 additions & 14 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1934,9 +1934,8 @@ static bool canSinkInstructions(
ArrayRef<Instruction *> Insts,
DenseMap<const Use *, SmallVector<Value *, 4>> &PHIOperands) {
// Prune out obviously bad instructions to move. Each instruction must have
// exactly zero or one use, and we check later that use is by a single, common
// PHI instruction in the successor.
bool HasUse = !Insts.front()->user_empty();
// the same number of uses, and we check later that the uses are consistent.
std::optional<unsigned> NumUses;
for (auto *I : Insts) {
// These instructions may change or break semantics if moved.
if (isa<PHINode>(I) || I->isEHPad() || isa<AllocaInst>(I) ||
Expand All @@ -1956,10 +1955,9 @@ static bool canSinkInstructions(
if (C->isInlineAsm() || C->cannotMerge() || C->isConvergent())
return false;

// Each instruction must have zero or one use.
if (HasUse && !I->hasOneUse())
return false;
if (!HasUse && !I->user_empty())
if (!NumUses)
NumUses = I->getNumUses();
else if (NumUses != I->getNumUses())
return false;
}

Expand Down Expand Up @@ -1987,8 +1985,7 @@ static bool canSinkInstructions(
// then the other phi operands must match the instructions from Insts. This
// also has to hold true for any phi nodes that would be created as a result
// of sinking. Both of these cases are represented by PhiOperands.
if (HasUse) {
const Use &U = *I0->use_begin();
for (const Use &U : I0->uses()) {
auto It = PHIOperands.find(&U);
if (It == PHIOperands.end())
// There may be uses in other blocks when sinking into a loop header.
Expand Down Expand Up @@ -2138,11 +2135,11 @@ static void sinkLastInstruction(ArrayRef<BasicBlock*> Blocks) {
I0->andIRFlags(I);
}

if (!I0->user_empty()) {
// canSinkLastInstruction checked that all instructions were used by
// one and only one PHI node. Find that now, RAUW it to our common
// instruction and nuke it.
auto *PN = cast<PHINode>(*I0->user_begin());
for (User *U : make_early_inc_range(I0->users())) {
// canSinkLastInstruction checked that all instructions are only used by
// phi nodes in a way that allows replacing the phi node with the common
// instruction.
auto *PN = cast<PHINode>(U);
PN->replaceAllUsesWith(I0);
PN->eraseFromParent();
}
Expand Down
46 changes: 16 additions & 30 deletions llvm/test/Transforms/SimplifyCFG/X86/sink-common-code.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -1704,19 +1704,14 @@ return:

define ptr @multi_use_in_phi(i1 %cond, ptr %p, i64 %a, i64 %b) {
; CHECK-LABEL: @multi_use_in_phi(
; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[JOIN:%.*]]
; CHECK: if:
; CHECK-NEXT: call void @dummy()
; CHECK-NEXT: [[GEP1_A:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
; CHECK-NEXT: br label [[JOIN:%.*]]
; CHECK: else:
; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P]], i64 [[A]]
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
; CHECK-NEXT: [[GEP1_B_SINK:%.*]] = phi ptr [ [[GEP1_B]], [[ELSE]] ], [ [[GEP1_A]], [[IF]] ]
; CHECK-NEXT: [[PHI1:%.*]] = phi ptr [ [[GEP1_A]], [[IF]] ], [ [[GEP1_B]], [[ELSE]] ]
; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B_SINK]], i64 [[B:%.*]]
; CHECK-NEXT: call void @use.ptr(ptr [[PHI1]])
; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[B:%.*]]
; CHECK-NEXT: call void @use.ptr(ptr [[GEP1_B]])
; CHECK-NEXT: ret ptr [[GEP2_B]]
;
br i1 %cond, label %if, label %else
Expand Down Expand Up @@ -1778,23 +1773,16 @@ join:

define i64 @multi_use_in_block(i1 %cond, ptr %p, i64 %a, i64 %b) {
; CHECK-LABEL: @multi_use_in_block(
; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[ELSE:%.*]]
; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF:%.*]], label [[JOIN:%.*]]
; CHECK: if:
; CHECK-NEXT: call void @dummy()
; CHECK-NEXT: [[GEP1_A:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
; CHECK-NEXT: [[V_A:%.*]] = load i64, ptr [[GEP1_A]], align 8
; CHECK-NEXT: [[GEP2_A:%.*]] = getelementptr i8, ptr [[GEP1_A]], i64 [[V_A]]
; CHECK-NEXT: br label [[JOIN:%.*]]
; CHECK: else:
; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P]], i64 [[A]]
; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[GEP1_B]], align 8
; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[V_B]]
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
; CHECK-NEXT: [[PHI1:%.*]] = phi i64 [ [[V_A]], [[IF]] ], [ [[V_B]], [[ELSE]] ]
; CHECK-NEXT: [[PHI2:%.*]] = phi ptr [ [[GEP2_A]], [[IF]] ], [ [[GEP2_B]], [[ELSE]] ]
; CHECK-NEXT: call void @use.ptr(ptr [[PHI2]])
; CHECK-NEXT: ret i64 [[PHI1]]
; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[GEP1_B]], align 8
; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[V_B]]
; CHECK-NEXT: call void @use.ptr(ptr [[GEP2_B]])
; CHECK-NEXT: ret i64 [[V_B]]
;
br i1 %cond, label %if, label %else

Expand Down Expand Up @@ -1824,19 +1812,17 @@ define i64 @multi_use_in_block_inconsistent(i1 %cond, ptr %p, i64 %a, i64 %b) {
; CHECK: if:
; CHECK-NEXT: call void @dummy()
; CHECK-NEXT: [[GEP1_A:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[A:%.*]]
; CHECK-NEXT: [[V_A:%.*]] = load i64, ptr [[GEP1_A]], align 8
; CHECK-NEXT: [[GEP2_A:%.*]] = getelementptr i8, ptr [[GEP1_A]], i64 [[V_A]]
; CHECK-NEXT: br label [[JOIN:%.*]]
; CHECK: else:
; CHECK-NEXT: [[GEP1_B:%.*]] = getelementptr i8, ptr [[P]], i64 [[A]]
; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[P]], align 8
; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B]], i64 [[V_B]]
; CHECK-NEXT: br label [[JOIN]]
; CHECK: join:
; CHECK-NEXT: [[PHI1:%.*]] = phi i64 [ [[V_A]], [[IF]] ], [ [[V_B]], [[ELSE]] ]
; CHECK-NEXT: [[PHI2:%.*]] = phi ptr [ [[GEP2_A]], [[IF]] ], [ [[GEP2_B]], [[ELSE]] ]
; CHECK-NEXT: call void @use.ptr(ptr [[PHI2]])
; CHECK-NEXT: ret i64 [[PHI1]]
; CHECK-NEXT: [[P_SINK:%.*]] = phi ptr [ [[P]], [[ELSE]] ], [ [[GEP1_A]], [[IF]] ]
; CHECK-NEXT: [[GEP1_B_SINK:%.*]] = phi ptr [ [[GEP1_B]], [[ELSE]] ], [ [[GEP1_A]], [[IF]] ]
; CHECK-NEXT: [[V_B:%.*]] = load i64, ptr [[P_SINK]], align 8
; CHECK-NEXT: [[GEP2_B:%.*]] = getelementptr i8, ptr [[GEP1_B_SINK]], i64 [[V_B]]
; CHECK-NEXT: call void @use.ptr(ptr [[GEP2_B]])
; CHECK-NEXT: ret i64 [[V_B]]
;
br i1 %cond, label %if, label %else

Expand Down
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