spatel created this revision.
spatel added reviewers: craig.topper, efriedma, lebedev.ri.
Herald added a subscriber: mcrosier.
The clang builtins have the same semantics as the stdlib functions.
The stdlib functions are defined in section 7.20.6.1 of the C standard with:
"If the result cannot be represented, the behavior is undefined."
So I think that lets us mark the negation with 'nsw' because "sub i32 0,
INT_MIN" would be UB/poison.
https://reviews.llvm.org/D47202
Files:
lib/CodeGen/CGBuiltin.cpp
test/CodeGen/builtin-abs.c
Index: test/CodeGen/builtin-abs.c
===================================================================
--- test/CodeGen/builtin-abs.c
+++ test/CodeGen/builtin-abs.c
@@ -2,25 +2,25 @@
int absi(int x) {
// CHECK-LABEL: @absi(
-// CHECK: [[NEG:%.*]] = sub i32 0, [[X:%.*]]
+// CHECK: [[NEG:%.*]] = sub nsw i32 0, [[X:%.*]]
// CHECK: [[CMP:%.*]] = icmp slt i32 [[X]], 0
// CHECK: [[SEL:%.*]] = select i1 [[CMP]], i32 [[NEG]], i32 [[X]]
//
return __builtin_abs(x);
}
long absl(long x) {
// CHECK-LABEL: @absl(
-// CHECK: [[NEG:%.*]] = sub i64 0, [[X:%.*]]
+// CHECK: [[NEG:%.*]] = sub nsw i64 0, [[X:%.*]]
// CHECK: [[CMP:%.*]] = icmp slt i64 [[X]], 0
// CHECK: [[SEL:%.*]] = select i1 [[CMP]], i64 [[NEG]], i64 [[X]]
//
return __builtin_labs(x);
}
long long absll(long long x) {
// CHECK-LABEL: @absll(
-// CHECK: [[NEG:%.*]] = sub i64 0, [[X:%.*]]
+// CHECK: [[NEG:%.*]] = sub nsw i64 0, [[X:%.*]]
// CHECK: [[CMP:%.*]] = icmp slt i64 [[X]], 0
// CHECK: [[SEL:%.*]] = select i1 [[CMP]], i64 [[NEG]], i64 [[X]]
//
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -1252,8 +1252,9 @@
case Builtin::BI__builtin_labs:
case Builtin::BI__builtin_llabs: {
// X < 0 ? -X : X
+ // The negation has 'nsw' because abs of INT_MIN is undefined.
Value *ArgValue = EmitScalarExpr(E->getArg(0));
- Value *NegOp = Builder.CreateNeg(ArgValue, "neg");
+ Value *NegOp = Builder.CreateNSWNeg(ArgValue, "neg");
Constant *Zero = llvm::Constant::getNullValue(ArgValue->getType());
Value *CmpResult = Builder.CreateICmpSLT(ArgValue, Zero, "abscond");
Value *Result = Builder.CreateSelect(CmpResult, NegOp, ArgValue, "abs");
Index: test/CodeGen/builtin-abs.c
===================================================================
--- test/CodeGen/builtin-abs.c
+++ test/CodeGen/builtin-abs.c
@@ -2,25 +2,25 @@
int absi(int x) {
// CHECK-LABEL: @absi(
-// CHECK: [[NEG:%.*]] = sub i32 0, [[X:%.*]]
+// CHECK: [[NEG:%.*]] = sub nsw i32 0, [[X:%.*]]
// CHECK: [[CMP:%.*]] = icmp slt i32 [[X]], 0
// CHECK: [[SEL:%.*]] = select i1 [[CMP]], i32 [[NEG]], i32 [[X]]
//
return __builtin_abs(x);
}
long absl(long x) {
// CHECK-LABEL: @absl(
-// CHECK: [[NEG:%.*]] = sub i64 0, [[X:%.*]]
+// CHECK: [[NEG:%.*]] = sub nsw i64 0, [[X:%.*]]
// CHECK: [[CMP:%.*]] = icmp slt i64 [[X]], 0
// CHECK: [[SEL:%.*]] = select i1 [[CMP]], i64 [[NEG]], i64 [[X]]
//
return __builtin_labs(x);
}
long long absll(long long x) {
// CHECK-LABEL: @absll(
-// CHECK: [[NEG:%.*]] = sub i64 0, [[X:%.*]]
+// CHECK: [[NEG:%.*]] = sub nsw i64 0, [[X:%.*]]
// CHECK: [[CMP:%.*]] = icmp slt i64 [[X]], 0
// CHECK: [[SEL:%.*]] = select i1 [[CMP]], i64 [[NEG]], i64 [[X]]
//
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -1252,8 +1252,9 @@
case Builtin::BI__builtin_labs:
case Builtin::BI__builtin_llabs: {
// X < 0 ? -X : X
+ // The negation has 'nsw' because abs of INT_MIN is undefined.
Value *ArgValue = EmitScalarExpr(E->getArg(0));
- Value *NegOp = Builder.CreateNeg(ArgValue, "neg");
+ Value *NegOp = Builder.CreateNSWNeg(ArgValue, "neg");
Constant *Zero = llvm::Constant::getNullValue(ArgValue->getType());
Value *CmpResult = Builder.CreateICmpSLT(ArgValue, Zero, "abscond");
Value *Result = Builder.CreateSelect(CmpResult, NegOp, ArgValue, "abs");
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