Merge #934

934: In LLVM backend, track which floats are guaranteed to be arithmetic, which makes the canonicalization a no-op. r=nlewycky a=nlewycky

# Description
This is a reimplementation of the patch in PR #651.

Extend state.rs ExtraInfo to track more information about floats. In addition to tracking whether the value has a pending canonicalization of NaNs, also track whether the value is known to be arithmetic (which includes infinities, regular values, and non-signalling NaNs (aka. "arithmetic NaNs" in the webassembly spec)). When the value is arithmetic, the correct sequence of operations to canonicalize the value is a no-op. Therefore, we create a lattice where pending+arithmetic=arithmetic.

Also, this extends the tracking to track all values, including non-SIMD integers. That's why there are more places where pending canonicalizations are applied.

Looking at c-wasm-simd128-example, this provides no performance change to the non-SIMD case (takes 58s on my noisy dev machine). The SIMD case drops from 46s to 29s.

# Review

- [ ] Add a short description of the the change to the CHANGELOG.md file


Co-authored-by: Nick Lewycky <nick@wasmer.io>

CHANGELOG.md

@@ -13,6 +13,7 @@
 - [#990](https://github.com/wasmerio/wasmer/pull/990) Default wasmer CLI to `run`.  Wasmer will now attempt to parse unrecognized command line options as if they were applied to the run command: `wasmer mywasm.wasm --dir=.` now works!
 - [#987](https://github.com/wasmerio/wasmer/pull/987) Fix `runtime-c-api` header files when compiled by gnuc.
 - [#957](https://github.com/wasmerio/wasmer/pull/957) Change the meaning of `wasmer_wasi::is_wasi_module` to detect any type of WASI module, add support for new wasi snapshot_preview1
+- [#934](https://github.com/wasmerio/wasmer/pull/934) Simplify float expressions in the LLVM backend.
 
 ## 0.10.2 - 2019-11-18
 

lib/llvm-backend/src/state.rs

@@ -4,6 +4,7 @@ use inkwell::{
 };
 use smallvec::SmallVec;
 use std::cell::Cell;
+use std::ops::{BitAnd, BitOr, BitOrAssign};
 use wasmparser::BinaryReaderError;
 
 #[derive(Debug)]
@@ -67,23 +68,127 @@ impl ControlFrame {
     }
 }
 
-#[derive(Debug, Eq, PartialEq, Copy, Clone, Hash)]
-pub enum ExtraInfo {
-    None,
-
-    // This values is required to be arithmetic 32-bit NaN (or 32x4) by the WAsm
-    // machine, but which might not be in the LLVM value. The conversion to
-    // arithmetic NaN is pending. It is required for correctness.
-    PendingF32NaN,
-
-    // This values is required to be arithmetic 64-bit NaN (or 64x2) by the WAsm
-    // machine, but which might not be in the LLVM value. The conversion to
-    // arithmetic NaN is pending. It is required for correctness.
-    PendingF64NaN,
+#[derive(Debug, Default, Eq, PartialEq, Copy, Clone, Hash)]
+pub struct ExtraInfo {
+    state: u8,
 }
-impl Default for ExtraInfo {
-    fn default() -> Self {
-        ExtraInfo::None
+impl ExtraInfo {
+    // This value is required to be arithmetic 32-bit NaN (or 32x4) by the WAsm
+    // machine, but which might not be in the LLVM value. The conversion to
+    // arithmetic NaN is pending. It is required for correctness.
+    //
+    // When applied to a 64-bit value, this flag has no meaning and must be
+    // ignored. It may be set in such cases to allow for common handling of
+    // 32 and 64-bit operations.
+    pub const fn pending_f32_nan() -> ExtraInfo {
+        ExtraInfo { state: 1 }
+    }
+
+    // This value is required to be arithmetic 64-bit NaN (or 64x2) by the WAsm
+    // machine, but which might not be in the LLVM value. The conversion to
+    // arithmetic NaN is pending. It is required for correctness.
+    //
+    // When applied to a 32-bit value, this flag has no meaning and must be
+    // ignored. It may be set in such cases to allow for common handling of
+    // 32 and 64-bit operations.
+    pub const fn pending_f64_nan() -> ExtraInfo {
+        ExtraInfo { state: 2 }
+    }
+
+    // This value either does not contain a 32-bit NaN, or it contains an
+    // arithmetic NaN. In SIMD, applies to all 4 lanes.
+    pub const fn arithmetic_f32() -> ExtraInfo {
+        ExtraInfo { state: 4 }
+    }
+
+    // This value either does not contain a 64-bit NaN, or it contains an
+    // arithmetic NaN. In SIMD, applies to both lanes.
+    pub const fn arithmetic_f64() -> ExtraInfo {
+        ExtraInfo { state: 8 }
+    }
+
+    pub const fn has_pending_f32_nan(&self) -> bool {
+        self.state & ExtraInfo::pending_f32_nan().state != 0
+    }
+    pub const fn has_pending_f64_nan(&self) -> bool {
+        self.state & ExtraInfo::pending_f64_nan().state != 0
+    }
+    pub const fn is_arithmetic_f32(&self) -> bool {
+        self.state & ExtraInfo::arithmetic_f32().state != 0
+    }
+    pub const fn is_arithmetic_f64(&self) -> bool {
+        self.state & ExtraInfo::arithmetic_f64().state != 0
+    }
+
+    pub const fn strip_pending(&self) -> ExtraInfo {
+        ExtraInfo {
+            state: self.state
+                & !(ExtraInfo::pending_f32_nan().state | ExtraInfo::pending_f64_nan().state),
+        }
+    }
+}
+
+// Union two ExtraInfos.
+impl BitOr for ExtraInfo {
+    type Output = Self;
+
+    fn bitor(self, other: Self) -> Self {
+        debug_assert!(!(self.has_pending_f32_nan() && other.has_pending_f64_nan()));
+        debug_assert!(!(self.has_pending_f64_nan() && other.has_pending_f32_nan()));
+        ExtraInfo {
+            state: if self.is_arithmetic_f32() || other.is_arithmetic_f32() {
+                ExtraInfo::arithmetic_f32().state
+            } else if self.has_pending_f32_nan() || other.has_pending_f32_nan() {
+                ExtraInfo::pending_f32_nan().state
+            } else {
+                0
+            } + if self.is_arithmetic_f64() || other.is_arithmetic_f64() {
+                ExtraInfo::arithmetic_f64().state
+            } else if self.has_pending_f64_nan() || other.has_pending_f64_nan() {
+                ExtraInfo::pending_f64_nan().state
+            } else {
+                0
+            },
+        }
+    }
+}
+impl BitOrAssign for ExtraInfo {
+    fn bitor_assign(&mut self, other: Self) {
+        *self = *self | other;
+    }
+}
+
+// Intersection for ExtraInfo.
+impl BitAnd for ExtraInfo {
+    type Output = Self;
+    fn bitand(self, other: Self) -> Self {
+        // Pending canonicalizations are not safe to discard, or even reorder.
+        assert!(
+            self.has_pending_f32_nan() == other.has_pending_f32_nan()
+                || self.is_arithmetic_f32()
+                || other.is_arithmetic_f32()
+        );
+        assert!(
+            self.has_pending_f64_nan() == other.has_pending_f64_nan()
+                || self.is_arithmetic_f64()
+                || other.is_arithmetic_f64()
+        );
+        let info = match (
+            self.is_arithmetic_f32() && other.is_arithmetic_f32(),
+            self.is_arithmetic_f64() && other.is_arithmetic_f64(),
+        ) {
+            (false, false) => Default::default(),
+            (true, false) => ExtraInfo::arithmetic_f32(),
+            (false, true) => ExtraInfo::arithmetic_f64(),
+            (true, true) => ExtraInfo::arithmetic_f32() | ExtraInfo::arithmetic_f64(),
+        };
+        let info = match (self.has_pending_f32_nan(), self.has_pending_f64_nan()) {
+            (false, false) => info,
+            (true, false) => info | ExtraInfo::pending_f32_nan(),
+            (false, true) => info | ExtraInfo::pending_f64_nan(),
+            (true, true) => unreachable!("Can't form ExtraInfo with two pending canonicalizations"),
+        };
+        info
     }
 }
 
@@ -165,7 +270,7 @@ impl State {
     }
 
     pub fn push1<T: BasicValue>(&mut self, value: T) {
-        self.push1_extra(value, ExtraInfo::None);
+        self.push1_extra(value, Default::default());
     }
 
     pub fn push1_extra<T: BasicValue>(&mut self, value: T, info: ExtraInfo) {
@@ -197,15 +302,6 @@ impl State {
         Ok((v1, v2))
     }
 
-    pub fn pop3(
-        &mut self,
-    ) -> Result<(BasicValueEnum, BasicValueEnum, BasicValueEnum), BinaryReaderError> {
-        let v3 = self.pop1()?;
-        let v2 = self.pop1()?;
-        let v1 = self.pop1()?;
-        Ok((v1, v2, v3))
-    }
-
     pub fn pop3_extra(
         &mut self,
     ) -> Result<