Cranelift: Constant propagate floats (#8954)

* const propagate `fadd`, `fsub`, `fmul`, `fdiv`

* add `sqrt`, `ceil`, `floor`, `trunc`, `nearest`

* todo

* bail if result is NaN

* add `fmin`, `fmax`

* `non_nan` helper methods

* explain why no const folding of NaNs

* use `f32`/`f64` `round_ties_even` methods

Those methods are stable since Rust version 1.77.0

cranelift/codegen/src/ir/immediates.rs

@@ -915,6 +915,11 @@ impl Ieee32 {
         self.as_f32().is_nan()
     }
 
+    /// Returns `None` if `self` is a NaN and `Some(self)` otherwise.
+    pub fn non_nan(self) -> Option<Self> {
+        Some(self).filter(|f| !f.is_nan())
+    }
+
     /// Converts Self to a rust f32
     pub fn as_f32(self) -> f32 {
         f32::from_bits(self.0)
@@ -927,17 +932,21 @@ impl Ieee32 {
 
     /// Computes the absolute value of self.
     pub fn abs(self) -> Self {
-        Self::with_float(self.as_f32().abs())
+        Self(self.0 & !(1u32 << 31))
     }
 
     /// Returns a number composed of the magnitude of self and the sign of sign.
     pub fn copysign(self, sign: Self) -> Self {
-        Self::with_float(self.as_f32().copysign(sign.as_f32()))
+        if self.is_negative() == sign.is_negative() {
+            self
+        } else {
+            self.neg()
+        }
     }
 
     /// Returns true if self has a negative sign, including -0.0, NaNs with negative sign bit and negative infinity.
     pub fn is_negative(&self) -> bool {
-        self.as_f32().is_sign_negative()
+        self.0 & (1 << 31) != 0
     }
 
     /// Returns true if self is positive or negative zero
@@ -963,17 +972,7 @@ impl Ieee32 {
     /// Returns the nearest integer to `self`. Rounds half-way cases to the number
     /// with an even least significant digit.
     pub fn round_ties_even(self) -> Self {
-        // TODO: Replace with the native implementation once
-        // https://github.com/rust-lang/rust/issues/96710 is stabilized
-        let toint_32: f32 = 1.0 / f32::EPSILON;
-
-        let f = self.as_f32();
-        let e = self.0 >> 23 & 0xff;
-        if e >= 0x7f_u32 + 23 {
-            self
-        } else {
-            Self::with_float((f.abs() + toint_32 - toint_32).copysign(f))
-        }
+        Self::with_float(self.as_f32().round_ties_even())
     }
 }
 
@@ -1017,7 +1016,7 @@ impl Neg for Ieee32 {
     type Output = Ieee32;
 
     fn neg(self) -> Self::Output {
-        Self::with_float(self.as_f32().neg())
+        Self(self.0 ^ (1 << 31))
     }
 }
 
@@ -1133,6 +1132,11 @@ impl Ieee64 {
         self.as_f64().is_nan()
     }
 
+    /// Returns `None` if `self` is a NaN and `Some(self)` otherwise.
+    pub fn non_nan(self) -> Option<Self> {
+        Some(self).filter(|f| !f.is_nan())
+    }
+
     /// Converts Self to a rust f64
     pub fn as_f64(self) -> f64 {
         f64::from_bits(self.0)
@@ -1145,17 +1149,21 @@ impl Ieee64 {
 
     /// Computes the absolute value of self.
     pub fn abs(self) -> Self {
-        Self::with_float(self.as_f64().abs())
+        Self(self.0 & !(1u64 << 63))
     }
 
     /// Returns a number composed of the magnitude of self and the sign of sign.
     pub fn copysign(self, sign: Self) -> Self {
-        Self::with_float(self.as_f64().copysign(sign.as_f64()))
+        if self.is_negative() == sign.is_negative() {
+            self
+        } else {
+            self.neg()
+        }
     }
 
     /// Returns true if self has a negative sign, including -0.0, NaNs with negative sign bit and negative infinity.
     pub fn is_negative(&self) -> bool {
-        self.as_f64().is_sign_negative()
+        self.0 & (1 << 63) != 0
     }
 
     /// Returns true if self is positive or negative zero
@@ -1181,17 +1189,7 @@ impl Ieee64 {
     /// Returns the nearest integer to `self`. Rounds half-way cases to the number
     /// with an even least significant digit.
     pub fn round_ties_even(self) -> Self {
-        // TODO: Replace with the native implementation once
-        // https://github.com/rust-lang/rust/issues/96710 is stabilized
-        let toint_64: f64 = 1.0 / f64::EPSILON;
-
-        let f = self.as_f64();
-        let e = self.0 >> 52 & 0x7ff_u64;
-        if e >= 0x3ff_u64 + 52 {
-            self
-        } else {
-            Self::with_float((f.abs() + toint_64 - toint_64).copysign(f))
-        }
+        Self::with_float(self.as_f64().round_ties_even())
     }
 }
 
@@ -1241,7 +1239,7 @@ impl Neg for Ieee64 {
     type Output = Ieee64;
 
     fn neg(self) -> Self::Output {
-        Self::with_float(self.as_f64().neg())
+        Self(self.0 ^ (1 << 63))
     }
 }
 

cranelift/codegen/src/isle_prelude.rs

@@ -950,6 +950,62 @@ macro_rules! isle_common_prelude_methods {
             a.copysign(b)
         }
 
+        fn f32_add(&mut self, lhs: Ieee32, rhs: Ieee32) -> Option<Ieee32> {
+            (lhs + rhs).non_nan()
+        }
+
+        fn f32_sub(&mut self, lhs: Ieee32, rhs: Ieee32) -> Option<Ieee32> {
+            (lhs - rhs).non_nan()
+        }
+
+        fn f32_mul(&mut self, lhs: Ieee32, rhs: Ieee32) -> Option<Ieee32> {
+            (lhs * rhs).non_nan()
+        }
+
+        fn f32_div(&mut self, lhs: Ieee32, rhs: Ieee32) -> Option<Ieee32> {
+            (lhs / rhs).non_nan()
+        }
+
+        fn f32_sqrt(&mut self, n: Ieee32) -> Option<Ieee32> {
+            n.sqrt().non_nan()
+        }
+
+        fn f32_ceil(&mut self, n: Ieee32) -> Option<Ieee32> {
+            n.ceil().non_nan()
+        }
+
+        fn f32_floor(&mut self, n: Ieee32) -> Option<Ieee32> {
+            n.floor().non_nan()
+        }
+
+        fn f32_trunc(&mut self, n: Ieee32) -> Option<Ieee32> {
+            n.trunc().non_nan()
+        }
+
+        fn f32_nearest(&mut self, n: Ieee32) -> Option<Ieee32> {
+            n.round_ties_even().non_nan()
+        }
+
+        fn f32_min(&mut self, a: Ieee32, b: Ieee32) -> Option<Ieee32> {
+            if a.is_nan() || b.is_nan() {
+                None
+            } else if a <= b {
+                Some(a)
+            } else {
+                Some(b)
+            }
+        }
+
+        fn f32_max(&mut self, a: Ieee32, b: Ieee32) -> Option<Ieee32> {
+            if a.is_nan() || b.is_nan() {
+                None
+            } else if a >= b {
+                Some(a)
+            } else {
+                Some(b)
+            }
+        }
+
         fn f32_neg(&mut self, n: Ieee32) -> Ieee32 {
             n.neg()
         }
@@ -962,6 +1018,62 @@ macro_rules! isle_common_prelude_methods {
             a.copysign(b)
         }
 
+        fn f64_add(&mut self, lhs: Ieee64, rhs: Ieee64) -> Option<Ieee64> {
+            (lhs + rhs).non_nan()
+        }
+
+        fn f64_sub(&mut self, lhs: Ieee64, rhs: Ieee64) -> Option<Ieee64> {
+            (lhs - rhs).non_nan()
+        }
+
+        fn f64_mul(&mut self, lhs: Ieee64, rhs: Ieee64) -> Option<Ieee64> {
+            (lhs * rhs).non_nan()
+        }
+
+        fn f64_div(&mut self, lhs: Ieee64, rhs: Ieee64) -> Option<Ieee64> {
+            (lhs / rhs).non_nan()
+        }
+
+        fn f64_sqrt(&mut self, n: Ieee64) -> Option<Ieee64> {
+            n.sqrt().non_nan()
+        }
+
+        fn f64_ceil(&mut self, n: Ieee64) -> Option<Ieee64> {
+            n.ceil().non_nan()
+        }
+
+        fn f64_floor(&mut self, n: Ieee64) -> Option<Ieee64> {
+            n.floor().non_nan()
+        }
+
+        fn f64_trunc(&mut self, n: Ieee64) -> Option<Ieee64> {
+            n.trunc().non_nan()
+        }
+
+        fn f64_nearest(&mut self, n: Ieee64) -> Option<Ieee64> {
+            n.round_ties_even().non_nan()
+        }
+
+        fn f64_min(&mut self, a: Ieee64, b: Ieee64) -> Option<Ieee64> {
+            if a.is_nan() || b.is_nan() {
+                None
+            } else if a <= b {
+                Some(a)
+            } else {
+                Some(b)
+            }
+        }
+
+        fn f64_max(&mut self, a: Ieee64, b: Ieee64) -> Option<Ieee64> {
+            if a.is_nan() || b.is_nan() {
+                None
+            } else if a >= b {
+                Some(a)
+            } else {
+                Some(b)
+            }
+        }
+
         fn f64_neg(&mut self, n: Ieee64) -> Ieee64 {
             n.neg()
         }

cranelift/codegen/src/opts/cprop.isle

@@ -182,8 +182,6 @@
       (if-let $true (u64_lt (i64_as_u64 (i64_neg k)) (i64_as_u64 k)))
       (iadd ty x (iconst ty (imm64_masked ty (i64_as_u64 (i64_neg k))))))
 
-;; TODO: fadd, fsub, fmul, fdiv, fneg, fabs
-
 ;; A splat of a constant can become a direct `vconst` with the appropriate bit
 ;; pattern.
 (rule (simplify (splat dst (iconst $I8 n)))
@@ -280,7 +278,92 @@
 (decl pure u64_bswap64 (u64) u64)
 (extern constructor u64_bswap64 u64_bswap64)
 
-;; Constant fold bitwise float operations (fneg/fabs/fcopysign)
+;; Constant fold float operations
+;; Note: With the exception of fabs, fneg and copysign,
+;; constant folding is only performed when the result of
+;; an instruction isn't NaN. We want the NaN bit patterns
+;; produced by an instruction to be consistent, and
+;; compile-time evaluation in a cross-compilation scenario
+;; risks producing different NaN bit patterns than the target
+;; would have at run-time.
+;; TODO: fcmp, fma, demote, promote, to-int ops
+(rule (simplify (fadd $F32 (f32const $F32 lhs) (f32const $F32 rhs)))
+      (if-let r (f32_add lhs rhs))
+      (subsume (f32const $F32 r)))
+(rule (simplify (fadd $F64 (f64const $F64 lhs) (f64const $F64 rhs)))
+      (if-let r (f64_add lhs rhs))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (fsub $F32 (f32const $F32 lhs) (f32const $F32 rhs)))
+      (if-let r (f32_sub lhs rhs))
+      (subsume (f32const $F32 r)))
+(rule (simplify (fsub $F64 (f64const $F64 lhs) (f64const $F64 rhs)))
+      (if-let r (f64_sub lhs rhs))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (fmul $F32 (f32const $F32 lhs) (f32const $F32 rhs)))
+      (if-let r (f32_mul lhs rhs))
+      (subsume (f32const $F32 r)))
+(rule (simplify (fmul $F64 (f64const $F64 lhs) (f64const $F64 rhs)))
+      (if-let r (f64_mul lhs rhs))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (fdiv $F32 (f32const $F32 lhs) (f32const $F32 rhs)))
+      (if-let r (f32_div lhs rhs))
+      (subsume (f32const $F32 r)))
+(rule (simplify (fdiv $F64 (f64const $F64 lhs) (f64const $F64 rhs)))
+      (if-let r (f64_div lhs rhs))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (sqrt $F32 (f32const $F32 n)))
+      (if-let r (f32_sqrt n))
+      (subsume (f32const $F32 r)))
+(rule (simplify (sqrt $F64 (f64const $F64 n)))
+      (if-let r (f64_sqrt n))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (ceil $F32 (f32const $F32 n)))
+      (if-let r (f32_ceil n))
+      (subsume (f32const $F32 r)))
+(rule (simplify (ceil $F64 (f64const $F64 n)))
+      (if-let r (f64_ceil n))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (floor $F32 (f32const $F32 n)))
+      (if-let r (f32_floor n))
+      (subsume (f32const $F32 r)))
+(rule (simplify (floor $F64 (f64const $F64 n)))
+      (if-let r (f64_floor n))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (trunc $F32 (f32const $F32 n)))
+      (if-let r (f32_trunc n))
+      (subsume (f32const $F32 r)))
+(rule (simplify (trunc $F64 (f64const $F64 n)))
+      (if-let r (f64_trunc n))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (nearest $F32 (f32const $F32 n)))
+      (if-let r (f32_nearest n))
+      (subsume (f32const $F32 r)))
+(rule (simplify (nearest $F64 (f64const $F64 n)))
+      (if-let r (f64_nearest n))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (fmin $F32 (f32const $F32 n) (f32const $F32 m)))
+      (if-let r (f32_min n m))
+      (subsume (f32const $F32 r)))
+(rule (simplify (fmin $F64 (f64const $F64 n) (f64const $F64 m)))
+      (if-let r (f64_min n m))
+      (subsume (f64const $F64 r)))
+
+(rule (simplify (fmax $F32 (f32const $F32 n) (f32const $F32 m)))
+      (if-let r (f32_max n m))
+      (subsume (f32const $F32 r)))
+(rule (simplify (fmax $F64 (f64const $F64 n) (f64const $F64 m)))
+      (if-let r (f64_max n m))
+      (subsume (f64const $F64 r)))
+
 (rule (simplify (fneg $F16 (f16const $F16 n)))
       (subsume (f16const $F16 (f16_neg n))))
 (rule (simplify (fneg $F32 (f32const $F32 n)))