cmd/compile: precompute constant square roots
If a program wants to evaluate math.Sqrt for any constant value
(for example, math.Sqrt(3)), we can replace that expression with
its evaluation (1.7320508075688772) at compile time, instead of
generating a SQRT assembly command or equivalent.
Adds tests that math.Sqrt generates the correct values. I also
compiled a short program and verified that the Sqrt expression was
replaced by a constant value in the "after opt" step.
Adds a short doc to the top of generic.rules explaining what the file
does and how other files interact with it.
Fixes #15543.
Change-Id: I6b6e63ac61cec50763a09ba581024adeee03d4fa
Reviewed-on: https://go-review.googlesource.com/27457
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/cmd/compile/internal/ssa/value.go b/src/cmd/compile/internal/ssa/value.go
index 867221b..d30ef27 100644
--- a/src/cmd/compile/internal/ssa/value.go
+++ b/src/cmd/compile/internal/ssa/value.go
@@ -26,6 +26,7 @@
// Auxiliary info for this value. The type of this information depends on the opcode and type.
// AuxInt is used for integer values, Aux is used for other values.
+ // Floats are stored in AuxInt using math.Float64bits(f).
AuxInt int64
Aux interface{}
