Move LLVM sqrt intrinsic to stable (for float and doubles).

On the hardware that we support, they are implemented
by instructions and have consistent behavior for -0.0,
values less than -0.0, infinity, and nan.

We will need to be careful to guarantee the same behavior
for untested hardware.

TEST=run_llvm_math_intrinsics_test

BUG=http://code.google.com/p/nativeclient/issues/detail?id=3378
R=jfb@chromium.org, mseaborn@chromium.org

Review URL: https://codereview.chromium.org/18559005

3 files changed, 18 insertions, 1 deletions

diff --git a/docs/PNaClLangRef.rst b/docs/PNaClLangRef.rst
index e48bebc84d..4f322a3eff 100644
--- a/docs/PNaClLangRef.rst
+++ b/docs/PNaClLangRef.rst
@@ -344,6 +344,12 @@ TODO(jfb): atomics
   supported with the i32 and i64 argument types (the types supported by
   C-style GCC builtins).
 
+* ``llvm.sqrt``
+
+  The overloaded ``llvm.sqrt`` intrinsic is only supported for float
+  and double arguments types. Unlike the standard LLVM intrinsic,
+  PNaCl guarantees that llvm.sqrt returns a QNaN for values less than -0.0.
+
 * ``llvm.stacksave``
 * ``llvm.stackrestore``
 * ``llvm.trap``
diff --git a/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp b/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
index 8bf0848fd7..890bb907b8 100644
--- a/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
+++ b/lib/Analysis/NaCl/PNaClABIVerifyModule.cpp
@@ -176,6 +176,8 @@ AllowedIntrinsics::AllowedIntrinsics(LLVMContext *Context) : Context(Context) {
   Type *I16 = Type::getInt16Ty(*Context);
   Type *I32 = Type::getInt32Ty(*Context);
   Type *I64 = Type::getInt64Ty(*Context);
+  Type *Float = Type::getFloatTy(*Context);
+  Type *Double = Type::getDoubleTy(*Context);
 
   // We accept bswap for a limited set of types (i16, i32, i64).  The
   // various backends are able to generate instructions to implement
@@ -197,6 +199,10 @@ AllowedIntrinsics::AllowedIntrinsics(LLVMContext *Context) : Context(Context) {
   addIntrinsic(Intrinsic::nacl_longjmp);
   addIntrinsic(Intrinsic::nacl_setjmp);
 
+  // For native sqrt instructions. Must guarantee when x < -0.0, sqrt(x) = NaN.
+  addIntrinsic(Intrinsic::sqrt, Float);
+  addIntrinsic(Intrinsic::sqrt, Double);
+
   // Stack save and restore are used to support C99 VLAs.
   addIntrinsic(Intrinsic::stacksave);
   addIntrinsic(Intrinsic::stackrestore);
@@ -299,7 +305,6 @@ bool AllowedIntrinsics::isAllowed(const Function *Func) {
     case Intrinsic::nacl_target_arch: // Used by translator self-build.
     case Intrinsic::powi: // Rounding not defined: support with fast-math?
     case Intrinsic::prefetch: // TODO(jfb): Use our own data-prefetch intrinsic instead.
-    case Intrinsic::sqrt: // Rounding is defined, but setting errno up to libm.
       return PNaClABIAllowDevIntrinsics;
   }
 }
diff --git a/test/NaCl/PNaClABI/intrinsics.ll b/test/NaCl/PNaClABI/intrinsics.ll
index 1c28cfd967..7c5e76e795 100644
--- a/test/NaCl/PNaClABI/intrinsics.ll
+++ b/test/NaCl/PNaClABI/intrinsics.ll
@@ -40,6 +40,9 @@ declare i64 @llvm.ctpop.i64(i64)
 
 declare void @llvm.trap()
 
+declare float @llvm.sqrt.f32(float)
+declare double @llvm.sqrt.f64(double)
+
 declare i8* @llvm.stacksave()
 declare void @llvm.stackrestore(i8*)
 
@@ -98,6 +101,9 @@ declare i8* @llvm.frameaddress(i32 %level)
 ; CHECK: Function llvm.returnaddress is a disallowed LLVM intrinsic
 declare i8* @llvm.returnaddress(i32 %level)
 
+; CHECK: Function llvm.sqrt.fp128 is a disallowed LLVM intrinsic
+declare fp128 @llvm.sqrt.fp128(fp128)
+
 ; The variants with 64-bit %len arguments are disallowed.
 ; CHECK: Function llvm.memcpy.p0i8.p0i8.i64 is a disallowed LLVM intrinsic
 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* %dest, i8* %src,