spatel created this revision.
spatel added reviewers: MatzeB, neildhar, nikic, aqjune, dmgreen.
Herald added a subscriber: mcrosier.
spatel requested review of this revision.
We got an unintended consequence of the optimizer getting smarter when
compiling in a non-standard mode, and there's no good way to inhibit those
optimizations at a later stage. The test is based on an example linked from
D92270 <https://reviews.llvm.org/D92270>.
We allow the "no-strict-float-cast-overflow" exception to normal C cast rules
to preserve legacy code that does not expect overflowing casts from FP to int
to produce UB. See D46236 <https://reviews.llvm.org/D46236> for details.
https://reviews.llvm.org/D115804
Files:
clang/lib/CodeGen/CGExprScalar.cpp
clang/test/CodeGen/no-junk-ftrunc.c
Index: clang/test/CodeGen/no-junk-ftrunc.c
===================================================================
--- clang/test/CodeGen/no-junk-ftrunc.c
+++ clang/test/CodeGen/no-junk-ftrunc.c
@@ -1,14 +1,23 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
// RUN: %clang_cc1 -S -fno-strict-float-cast-overflow %s -emit-llvm -o - |
FileCheck %s --check-prefix=NOSTRICT
+
+// When compiling with non-standard semantics, use intrinsics to inhibit the
optimizer.
+
// NOSTRICT-LABEL: main
+// NOSTRICT: call i32 @llvm.fptosi.sat.i32.f64
+// NOSTRICT: call i32 @llvm.fptoui.sat.i32.f64
// NOSTRICT: attributes #0 = {{.*}}"strict-float-cast-overflow"="false"{{.*}}
// The workaround attribute is not applied by default.
// RUN: %clang_cc1 -S %s -emit-llvm -o - | FileCheck %s --check-prefix=STRICT
// STRICT-LABEL: main
+// STRICT: = fptosi
+// STRICT: = fptoui
// STRICT-NOT: strict-float-cast-overflow
+
int main() {
- return 0;
+ double d = 1e20;
+ return (int)d != 1e20 && (unsigned)d != 1e20;
}
-
Index: clang/lib/CodeGen/CGExprScalar.cpp
===================================================================
--- clang/lib/CodeGen/CGExprScalar.cpp
+++ clang/lib/CodeGen/CGExprScalar.cpp
@@ -1240,7 +1240,18 @@
if (isa<llvm::IntegerType>(DstElementTy)) {
assert(SrcElementTy->isFloatingPointTy() && "Unknown real conversion");
- if (DstElementType->isSignedIntegerOrEnumerationType())
+ bool IsSigned = DstElementType->isSignedIntegerOrEnumerationType();
+
+ // If we can't recognize overflow as undefined behavior, assume that
+ // overflow saturates. This protects against normal optimizations if we are
+ // compiling with non-standard FP semantics.
+ if (!CGF.CGM.getCodeGenOpts().StrictFloatCastOverflow) {
+ llvm::Intrinsic::ID IID =
+ IsSigned ? llvm::Intrinsic::fptosi_sat : llvm::Intrinsic::fptoui_sat;
+ return Builder.CreateCall(CGF.CGM.getIntrinsic(IID, {DstTy, SrcTy}),
Src);
+ }
+
+ if (IsSigned)
return Builder.CreateFPToSI(Src, DstTy, "conv");
return Builder.CreateFPToUI(Src, DstTy, "conv");
}
Index: clang/test/CodeGen/no-junk-ftrunc.c
===================================================================
--- clang/test/CodeGen/no-junk-ftrunc.c
+++ clang/test/CodeGen/no-junk-ftrunc.c
@@ -1,14 +1,23 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
// RUN: %clang_cc1 -S -fno-strict-float-cast-overflow %s -emit-llvm -o - | FileCheck %s --check-prefix=NOSTRICT
+
+// When compiling with non-standard semantics, use intrinsics to inhibit the optimizer.
+
// NOSTRICT-LABEL: main
+// NOSTRICT: call i32 @llvm.fptosi.sat.i32.f64
+// NOSTRICT: call i32 @llvm.fptoui.sat.i32.f64
// NOSTRICT: attributes #0 = {{.*}}"strict-float-cast-overflow"="false"{{.*}}
// The workaround attribute is not applied by default.
// RUN: %clang_cc1 -S %s -emit-llvm -o - | FileCheck %s --check-prefix=STRICT
// STRICT-LABEL: main
+// STRICT: = fptosi
+// STRICT: = fptoui
// STRICT-NOT: strict-float-cast-overflow
+
int main() {
- return 0;
+ double d = 1e20;
+ return (int)d != 1e20 && (unsigned)d != 1e20;
}
-
Index: clang/lib/CodeGen/CGExprScalar.cpp
===================================================================
--- clang/lib/CodeGen/CGExprScalar.cpp
+++ clang/lib/CodeGen/CGExprScalar.cpp
@@ -1240,7 +1240,18 @@
if (isa<llvm::IntegerType>(DstElementTy)) {
assert(SrcElementTy->isFloatingPointTy() && "Unknown real conversion");
- if (DstElementType->isSignedIntegerOrEnumerationType())
+ bool IsSigned = DstElementType->isSignedIntegerOrEnumerationType();
+
+ // If we can't recognize overflow as undefined behavior, assume that
+ // overflow saturates. This protects against normal optimizations if we are
+ // compiling with non-standard FP semantics.
+ if (!CGF.CGM.getCodeGenOpts().StrictFloatCastOverflow) {
+ llvm::Intrinsic::ID IID =
+ IsSigned ? llvm::Intrinsic::fptosi_sat : llvm::Intrinsic::fptoui_sat;
+ return Builder.CreateCall(CGF.CGM.getIntrinsic(IID, {DstTy, SrcTy}), Src);
+ }
+
+ if (IsSigned)
return Builder.CreateFPToSI(Src, DstTy, "conv");
return Builder.CreateFPToUI(Src, DstTy, "conv");
}
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