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[clang codegen] Emit !unpredictable metadata more consistently. #111065

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[clang codegen] Emit !unpredictable metadata more consistently. #111065

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10 changes: 9 additions & 1 deletion clang/lib/CodeGen/CGExprScalar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5338,7 +5338,15 @@ VisitAbstractConditionalOperator(const AbstractConditionalOperator *E) {
assert(!RHS && "LHS and RHS types must match");
return nullptr;
}
return Builder.CreateSelect(CondV, LHS, RHS, "cond");
llvm::Value *Select = Builder.CreateSelect(CondV, LHS, RHS, "cond");
if (auto *SelectI = dyn_cast<llvm::Instruction>(Select)) {
if (llvm::MDNode *Unpredictable =
CGF.getUnpredictableMetadata(condExpr)) {
SelectI->setMetadata(llvm::LLVMContext::MD_unpredictable,
Unpredictable);
}
}
return Select;
}

// If the top of the logical operator nest, reset the MCDC temp to 0.
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13 changes: 2 additions & 11 deletions clang/lib/CodeGen/CGStmt.cpp
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Expand Up @@ -2257,17 +2257,8 @@ void CodeGenFunction::EmitSwitchStmt(const SwitchStmt &S) {
EmitBlock(SwitchExit.getBlock(), true);
incrementProfileCounter(&S);

// If the switch has a condition wrapped by __builtin_unpredictable,
// create metadata that specifies that the switch is unpredictable.
// Don't bother if not optimizing because that metadata would not be used.
auto *Call = dyn_cast<CallExpr>(S.getCond());
if (Call && CGM.getCodeGenOpts().OptimizationLevel != 0) {
auto *FD = dyn_cast_or_null<FunctionDecl>(Call->getCalleeDecl());
if (FD && FD->getBuiltinID() == Builtin::BI__builtin_unpredictable) {
llvm::MDBuilder MDHelper(getLLVMContext());
SwitchInsn->setMetadata(llvm::LLVMContext::MD_unpredictable,
MDHelper.createUnpredictable());
}
if (llvm::MDNode *Unpredictable = getUnpredictableMetadata(S.getCond())) {
SwitchInsn->setMetadata(llvm::LLVMContext::MD_unpredictable, Unpredictable);
}

if (SwitchWeights) {
Expand Down
29 changes: 16 additions & 13 deletions clang/lib/CodeGen/CodeGenFunction.cpp
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Expand Up @@ -1820,6 +1820,21 @@ void CodeGenFunction::EmitBranchToCounterBlock(
EmitBranch(NextBlock);
}

llvm::MDNode *CodeGenFunction::getUnpredictableMetadata(const Expr *Cond) {
// If the branch has a condition wrapped by __builtin_unpredictable,
// create metadata that specifies that the branch is unpredictable.
// Don't bother if not optimizing because that metadata would not be used.
auto *Call = dyn_cast<CallExpr>(Cond->IgnoreImpCasts());
if (Call && CGM.getCodeGenOpts().OptimizationLevel != 0) {
auto *FD = dyn_cast_or_null<FunctionDecl>(Call->getCalleeDecl());
if (FD && FD->getBuiltinID() == Builtin::BI__builtin_unpredictable) {
llvm::MDBuilder MDHelper(getLLVMContext());
return MDHelper.createUnpredictable();
}
}
return nullptr;
}

/// EmitBranchOnBoolExpr - Emit a branch on a boolean condition (e.g. for an if
/// statement) to the specified blocks. Based on the condition, this might try
/// to simplify the codegen of the conditional based on the branch.
Expand Down Expand Up @@ -2046,19 +2061,7 @@ void CodeGenFunction::EmitBranchOnBoolExpr(
}

llvm::MDNode *Weights = nullptr;
llvm::MDNode *Unpredictable = nullptr;

// If the branch has a condition wrapped by __builtin_unpredictable,
// create metadata that specifies that the branch is unpredictable.
// Don't bother if not optimizing because that metadata would not be used.
auto *Call = dyn_cast<CallExpr>(Cond->IgnoreImpCasts());
if (Call && CGM.getCodeGenOpts().OptimizationLevel != 0) {
auto *FD = dyn_cast_or_null<FunctionDecl>(Call->getCalleeDecl());
if (FD && FD->getBuiltinID() == Builtin::BI__builtin_unpredictable) {
llvm::MDBuilder MDHelper(getLLVMContext());
Unpredictable = MDHelper.createUnpredictable();
}
}
llvm::MDNode *Unpredictable = getUnpredictableMetadata(Cond);

// If there is a Likelihood knowledge for the cond, lower it.
// Note that if not optimizing this won't emit anything.
Expand Down
5 changes: 5 additions & 0 deletions clang/lib/CodeGen/CodeGenFunction.h
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Expand Up @@ -5044,6 +5044,11 @@ class CodeGenFunction : public CodeGenTypeCache {
Stmt::Likelihood LH = Stmt::LH_None,
const Expr *CntrIdx = nullptr);

// getUnpredictableMetadata - If the expression is a call to
// __builtin_unpredictable, get the corresponding metadata. Otherwise returns
// nullptr.
llvm::MDNode *getUnpredictableMetadata(const Expr *Cond);

/// EmitBranchOnBoolExpr - Emit a branch on a boolean condition (e.g. for an
/// if statement) to the specified blocks. Based on the condition, this might
/// try to simplify the codegen of the conditional based on the branch.
Expand Down
20 changes: 16 additions & 4 deletions clang/test/CodeGen/builtin-unpredictable.c
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -disable-llvm-passes -o - %s -O1 | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -disable-llvm-passes -o - -x c++ %s -O1 | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -disable-llvm-passes -o - %s -O1 | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -disable-llvm-passes -o - -x c++ %s -O1 | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O0 | FileCheck %s --check-prefix=CHECK_O0

// When optimizing, the builtin should be converted to metadata.
Expand All @@ -18,7 +18,7 @@ void branch(int x) {
// CHECK: !unpredictable [[METADATA:.+]]

// CHECK_O0-NOT: builtin_unpredictable
// CHECK_O0-NOT: !unpredictable
// CHECK_O0-NOT: !unpredictable

if (__builtin_unpredictable(x > 0))
foo ();
Expand All @@ -31,7 +31,7 @@ int unpredictable_switch(int x) {
// CHECK: !unpredictable [[METADATA:.+]]

// CHECK_O0-NOT: builtin_unpredictable
// CHECK_O0-NOT: !unpredictable
// CHECK_O0-NOT: !unpredictable

switch(__builtin_unpredictable(x)) {
default:
Expand All @@ -47,6 +47,18 @@ int unpredictable_switch(int x) {
return 0;
}

int unpredictable_select(int x) {
// CHECK-LABEL: @unpredictable_select(

// CHECK-NOT: builtin_unpredictable
// CHECK: !unpredictable [[METADATA:.+]]

// CHECK_O0-NOT: builtin_unpredictable
// CHECK_O0-NOT: !unpredictable

return __builtin_unpredictable(x) ? 1 : 33;
}

#ifdef __cplusplus
}
#endif
Expand Down
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