Restore the sqrt -> llvm.sqrt mapping in fast-math mode
This restores the sqrt -> llvm.sqrt mapping, but only in fast-math mode
(specifically, when the UnsafeFPMath or NoNaNsFPMath CodeGen options are
enabled). The @llvm.sqrt* intrinsics have slightly different semantics from the
libm call, specifically, they are undefined when given a non-zero negative
number (the libm calls will always return NaN for any negative number).
This mapping was removed in r100613, and replaced with a TODO, but at that time
the fast-math flags were not yet implemented. Now that we have these, restoring
this mapping is important because it will enable autovectorization of sqrt
calls in loops (at least in fast-math mode).
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190646 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGBuiltin.cpp b/lib/CodeGen/CGBuiltin.cpp
index 5b5b39f..e6cfe64 100644
--- a/lib/CodeGen/CGBuiltin.cpp
+++ b/lib/CodeGen/CGBuiltin.cpp
@@ -1282,12 +1282,19 @@
case Builtin::BIsqrt:
case Builtin::BIsqrtf:
case Builtin::BIsqrtl: {
- // TODO: there is currently no set of optimizer flags
- // sufficient for us to rewrite sqrt to @llvm.sqrt.
- // -fmath-errno=0 is not good enough; we need finiteness.
- // We could probably precondition the call with an ult
- // against 0, but is that worth the complexity?
- break;
+ // Transform a call to sqrt* into a @llvm.sqrt.* intrinsic call, but only
+ // in finite- or unsafe-math mode (the intrinsic has different semantics
+ // for handling negative numbers compared to the library function, so
+ // -fmath-errno=0 is not enough).
+ if (!FD->hasAttr<ConstAttr>())
+ break;
+ if (!(CGM.getCodeGenOpts().UnsafeFPMath ||
+ CGM.getCodeGenOpts().NoNaNsFPMath))
+ break;
+ Value *Arg0 = EmitScalarExpr(E->getArg(0));
+ llvm::Type *ArgType = Arg0->getType();
+ Value *F = CGM.getIntrinsic(Intrinsic::sqrt, ArgType);
+ return RValue::get(Builder.CreateCall(F, Arg0));
}
case Builtin::BIpow: