cmd/compile/internal/ssa: fix PPC64 merging of (AND (S[RL]Dconst ...)

CL 622236 forgot to check the mask was also a 32 bit rotate mask. Add
a modified version of isPPC64WordRotateMask which valids the mask is
contiguous and fits inside a uint32.

I don't this is possible when merging SRDconst, the first check should
always reject such combines. But, be extra careful and do it there
too.

Fixes #73153

Change-Id: Ie95f74ec5e7d89dc761511126db814f886a7a435
Reviewed-on: https://go-review.googlesource.com/c/go/+/679775
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Jayanth Krishnamurthy <jayanth.krishnamurthy@ibm.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 17 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index b32823283b..eb2c3b31b8 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -1583,6 +1583,11 @@ func GetPPC64Shiftme(auxint int64) int64 {
 // operation.  Masks can also extend from the msb and wrap to
 // the lsb too.  That is, the valid masks are 32 bit strings
 // of the form: 0..01..10..0 or 1..10..01..1 or 1...1
+//
+// Note: This ignores the upper 32 bits of the input. When a
+// zero extended result is desired (e.g a 64 bit result), the
+// user must verify the upper 32 bits are 0 and the mask is
+// contiguous (that is, non-wrapping).
 func isPPC64WordRotateMask(v64 int64) bool {
 	// Isolate rightmost 1 (if none 0) and add.
 	v := uint32(v64)
@@ -1593,6 +1598,16 @@ func isPPC64WordRotateMask(v64 int64) bool {
 	return (v&vp == 0 || vn&vpn == 0) && v != 0
 }
 
+// Test if this mask is a valid, contiguous bitmask which can be
+// represented by a RLWNM mask and also clears the upper 32 bits
+// of the register.
+func isPPC64WordRotateMaskNonWrapping(v64 int64) bool {
+	// Isolate rightmost 1 (if none 0) and add.
+	v := uint32(v64)
+	vp := (v & -v) + v
+	return (v&vp == 0) && v != 0 && uint64(uint32(v64)) == uint64(v64)
+}
+
 // Compress mask and shift into single value of the form
 // me | mb<<8 | rotate<<16 | nbits<<24 where me and mb can
 // be used to regenerate the input mask.
@@ -1702,7 +1717,7 @@ func mergePPC64AndSrdi(m, s int64) int64 {
 	if rv&uint64(mask) != 0 {
 		return 0
 	}
-	if !isPPC64WordRotateMask(mask) {
+	if !isPPC64WordRotateMaskNonWrapping(mask) {
 		return 0
 	}
 	return encodePPC64RotateMask((32-s)&31, mask, 32)
@@ -1717,7 +1732,7 @@ func mergePPC64AndSldi(m, s int64) int64 {
 	if rv&uint64(mask) != 0 {
 		return 0
 	}
-	if !isPPC64WordRotateMask(mask) {
+	if !isPPC64WordRotateMaskNonWrapping(mask) {
 		return 0
 	}
 	return encodePPC64RotateMask(s&31, mask, 32)