runtime: add support for math intrinsics where supported

In particular, add support for a few math intrinsics for WebAssembly,
but add a few intrinsics to other systems as well at the same time. Some
may be missing still but will be easy to add if needed.

This increases the performance of one example by 50% to 100% depending
on the browser: the bottleneck was the inefficient sqrt implementation.

src/runtime/math.go

@@ -56,7 +56,15 @@ func math_Cbrt(x float64) float64 { return math_cbrt(x) }
 func math_cbrt(x float64) float64
 
 //go:linkname math_Ceil math.Ceil
-func math_Ceil(x float64) float64 { return math_ceil(x) }
+func math_Ceil(x float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_ceil(x)
+	}
+	return math_ceil(x)
+}
+
+//go:export llvm.ceil.f64
+func llvm_ceil(x float64) float64
 
 //go:linkname math_ceil math.ceil
 func math_ceil(x float64) float64
@@ -104,7 +112,15 @@ func math_Exp2(x float64) float64 { return math_exp2(x) }
 func math_exp2(x float64) float64
 
 //go:linkname math_Floor math.Floor
-func math_Floor(x float64) float64 { return math_floor(x) }
+func math_Floor(x float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_floor(x)
+	}
+	return math_floor(x)
+}
+
+//go:export llvm.floor.f64
+func llvm_floor(x float64) float64
 
 //go:linkname math_floor math.floor
 func math_floor(x float64) float64
@@ -152,13 +168,29 @@ func math_Log2(x float64) float64 { return math_log2(x) }
 func math_log2(x float64) float64
 
 //go:linkname math_Max math.Max
-func math_Max(x, y float64) float64 { return math_max(x, y) }
+func math_Max(x, y float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_maximum(x, y)
+	}
+	return math_max(x, y)
+}
+
+//go:export llvm.maximum.f64
+func llvm_maximum(x, y float64) float64
 
 //go:linkname math_max math.max
 func math_max(x, y float64) float64
 
 //go:linkname math_Min math.Min
-func math_Min(x, y float64) float64 { return math_min(x, y) }
+func math_Min(x, y float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_minimum(x, y)
+	}
+	return math_min(x, y)
+}
+
+//go:export llvm.minimum.f64
+func llvm_minimum(x, y float64) float64
 
 //go:linkname math_min math.min
 func math_min(x, y float64) float64
@@ -200,7 +232,15 @@ func math_Sinh(x float64) float64 { return math_sinh(x) }
 func math_sinh(x float64) float64
 
 //go:linkname math_Sqrt math.Sqrt
-func math_Sqrt(x float64) float64 { return math_sqrt(x) }
+func math_Sqrt(x float64) float64 {
+	if GOARCH == "x86" || GOARCH == "amd64" || GOARCH == "wasm" {
+		return llvm_sqrt(x)
+	}
+	return math_sqrt(x)
+}
+
+//go:export llvm.sqrt.f64
+func llvm_sqrt(x float64) float64
 
 //go:linkname math_sqrt math.sqrt
 func math_sqrt(x float64) float64
@@ -218,7 +258,15 @@ func math_Tanh(x float64) float64 { return math_tanh(x) }
 func math_tanh(x float64) float64
 
 //go:linkname math_Trunc math.Trunc
-func math_Trunc(x float64) float64 { return math_trunc(x) }
+func math_Trunc(x float64) float64 {
+	if GOARCH == "arm64" || GOARCH == "wasm" {
+		return llvm_trunc(x)
+	}
+	return math_trunc(x)
+}
+
+//go:export llvm.trunc.f64
+func llvm_trunc(x float64) float64
 
 //go:linkname math_trunc math.trunc
 func math_trunc(x float64) float64