[dev.ssa] cmd/compile: decompose 64-bit integer on ARM

Introduce dec64 rules to (generically) decompose 64-bit integer on
32-bit architectures. 64-bit integer is composed/decomposed with
Int64Make/Hi/Lo ops, as for complex types.

The idea of dealing with Add64 is the following:

(Add64 (Int64Make xh xl) (Int64Make yh yl))
->
(Int64Make
	(Add32withcarry xh yh (Select0 (Add32carry xl yl)))
	(Select1 (Add32carry xl yl)))

where Add32carry returns a tuple (flags,uint32). Select0 and Select1
read the first and the second component of the tuple, respectively.
The two Add32carry will be CSE'd.

Similarly for multiplication, Mul32uhilo returns a tuple (hi, lo).

Also add support of KeepAlive, to fix build after merge.

Tests addressed_ssa.go, array_ssa.go, break_ssa.go, chan_ssa.go,
cmp_ssa.go, ctl_ssa.go, map_ssa.go, and string_ssa.go in
cmd/compile/internal/gc/testdata passed.

Progress on SSA for ARM. Still not complete.

Updates #15365.

Change-Id: I7867c76785a456312de5d8398a6b3f7ca5a4f7ec
Reviewed-on: https://go-review.googlesource.com/23213
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/flagalloc.go b/src/cmd/compile/internal/ssa/flagalloc.go
index c6dc8d7f91..85c75e99d6 100644
--- a/src/cmd/compile/internal/ssa/flagalloc.go
+++ b/src/cmd/compile/internal/ssa/flagalloc.go
@@ -95,9 +95,18 @@ func flagalloc(f *Func) {
 					continue
 				}
 				// Recalculate a
+				var c1 *Value
+				if a.Op == OpARMCarry {
+					// Pseudo-op does not generate flags, its arg actually does
+					//TODO: generalize this condition?
+					c1 = a.Args[0].copyInto(b)
+				}
 				c := a.copyInto(b)
 				// Update v.
 				v.SetArg(i, c)
+				if c1 != nil {
+					c.SetArg(0, c1)
+				}
 				// Remember the most-recently computed flag value.
 				flag = a
 			}