cmd/compile: make pre-elimination of rulegen bounds checks more precise

In cases in which we had a named value whose args were all _,
like this rule from ARM.rules:

(MOVBUreg x:(MOVBUload _ _)) -> (MOVWreg x)

We previously inserted

_ = x.Args[1]

even though it is unnecessary.
This change eliminates this pointless bounds check.
And in other cases, we now check bounds just as far as strictly necessary.

No significant movement on any compiler metrics.
Just nicer (and less) code.

Passes toolstash-check -all.

Change-Id: I075dfe9f926cc561cdc705e9ddaab563164bed3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/221781
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 16 insertions, 76 deletions

diff --git a/src/cmd/compile/internal/ssa/rewriteARM64.go b/src/cmd/compile/internal/ssa/rewriteARM64.go
index 99beedcea1..4d1ed50d9b 100644
--- a/src/cmd/compile/internal/ssa/rewriteARM64.go
+++ b/src/cmd/compile/internal/ssa/rewriteARM64.go
@@ -4118,11 +4118,10 @@ func rewriteValueARM64_OpARM64FMOVDload(v *Value) bool {
 		if v_1.Op != OpARM64MOVDstore || v_1.AuxInt != off || v_1.Aux != sym {
 			break
 		}
-		_ = v_1.Args[2]
+		val := v_1.Args[1]
 		if ptr != v_1.Args[0] {
 			break
 		}
-		val := v_1.Args[1]
 		v.reset(OpARM64FMOVDgpfp)
 		v.AddArg(val)
 		return true
@@ -4366,11 +4365,10 @@ func rewriteValueARM64_OpARM64FMOVSload(v *Value) bool {
 		if v_1.Op != OpARM64MOVWstore || v_1.AuxInt != off || v_1.Aux != sym {
 			break
 		}
-		_ = v_1.Args[2]
+		val := v_1.Args[1]
 		if ptr != v_1.Args[0] {
 			break
 		}
-		val := v_1.Args[1]
 		v.reset(OpARM64FMOVSgpfp)
 		v.AddArg(val)
 		return true
@@ -6838,7 +6836,6 @@ func rewriteValueARM64_OpARM64MOVBUload(v *Value) bool {
 		}
 		off2 := v_1.AuxInt
 		sym2 := v_1.Aux
-		_ = v_1.Args[1]
 		ptr2 := v_1.Args[0]
 		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
 			break
@@ -6903,9 +6900,8 @@ func rewriteValueARM64_OpARM64MOVBUloadidx(v *Value) bool {
 		if v_2.Op != OpARM64MOVBstorezeroidx {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2) || isSamePtr(ptr, idx2) && isSamePtr(idx, ptr2)) {
 			break
 		}
@@ -6924,7 +6920,6 @@ func rewriteValueARM64_OpARM64MOVBUreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -6936,7 +6931,6 @@ func rewriteValueARM64_OpARM64MOVBUreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -7103,7 +7097,6 @@ func rewriteValueARM64_OpARM64MOVBload(v *Value) bool {
 		}
 		off2 := v_1.AuxInt
 		sym2 := v_1.Aux
-		_ = v_1.Args[1]
 		ptr2 := v_1.Args[0]
 		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
 			break
@@ -7155,9 +7148,8 @@ func rewriteValueARM64_OpARM64MOVBloadidx(v *Value) bool {
 		if v_2.Op != OpARM64MOVBstorezeroidx {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2) || isSamePtr(ptr, idx2) && isSamePtr(idx, ptr2)) {
 			break
 		}
@@ -7176,7 +7168,6 @@ func rewriteValueARM64_OpARM64MOVBreg(v *Value) bool {
 		if x.Op != OpARM64MOVBload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -7188,7 +7179,6 @@ func rewriteValueARM64_OpARM64MOVBreg(v *Value) bool {
 		if x.Op != OpARM64MOVBloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -9277,11 +9267,10 @@ func rewriteValueARM64_OpARM64MOVDload(v *Value) bool {
 		if v_1.Op != OpARM64FMOVDstore || v_1.AuxInt != off || v_1.Aux != sym {
 			break
 		}
-		_ = v_1.Args[2]
+		val := v_1.Args[1]
 		if ptr != v_1.Args[0] {
 			break
 		}
-		val := v_1.Args[1]
 		v.reset(OpARM64FMOVDfpgp)
 		v.AddArg(val)
 		return true
@@ -9379,7 +9368,6 @@ func rewriteValueARM64_OpARM64MOVDload(v *Value) bool {
 		}
 		off2 := v_1.AuxInt
 		sym2 := v_1.Aux
-		_ = v_1.Args[1]
 		ptr2 := v_1.Args[0]
 		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
 			break
@@ -9470,9 +9458,8 @@ func rewriteValueARM64_OpARM64MOVDloadidx(v *Value) bool {
 		if v_2.Op != OpARM64MOVDstorezeroidx {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2) || isSamePtr(ptr, idx2) && isSamePtr(idx, ptr2)) {
 			break
 		}
@@ -9509,9 +9496,8 @@ func rewriteValueARM64_OpARM64MOVDloadidx8(v *Value) bool {
 		if v_2.Op != OpARM64MOVDstorezeroidx8 {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2)) {
 			break
 		}
@@ -10145,7 +10131,6 @@ func rewriteValueARM64_OpARM64MOVHUload(v *Value) bool {
 		}
 		off2 := v_1.AuxInt
 		sym2 := v_1.Aux
-		_ = v_1.Args[1]
 		ptr2 := v_1.Args[0]
 		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
 			break
@@ -10255,9 +10240,8 @@ func rewriteValueARM64_OpARM64MOVHUloadidx(v *Value) bool {
 		if v_2.Op != OpARM64MOVHstorezeroidx {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2) || isSamePtr(ptr, idx2) && isSamePtr(idx, ptr2)) {
 			break
 		}
@@ -10294,9 +10278,8 @@ func rewriteValueARM64_OpARM64MOVHUloadidx2(v *Value) bool {
 		if v_2.Op != OpARM64MOVHstorezeroidx2 {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2)) {
 			break
 		}
@@ -10315,7 +10298,6 @@ func rewriteValueARM64_OpARM64MOVHUreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10327,7 +10309,6 @@ func rewriteValueARM64_OpARM64MOVHUreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10339,7 +10320,6 @@ func rewriteValueARM64_OpARM64MOVHUreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10351,7 +10331,6 @@ func rewriteValueARM64_OpARM64MOVHUreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10363,7 +10342,6 @@ func rewriteValueARM64_OpARM64MOVHUreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUloadidx2 {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10548,7 +10526,6 @@ func rewriteValueARM64_OpARM64MOVHload(v *Value) bool {
 		}
 		off2 := v_1.AuxInt
 		sym2 := v_1.Aux
-		_ = v_1.Args[1]
 		ptr2 := v_1.Args[0]
 		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
 			break
@@ -10645,9 +10622,8 @@ func rewriteValueARM64_OpARM64MOVHloadidx(v *Value) bool {
 		if v_2.Op != OpARM64MOVHstorezeroidx {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2) || isSamePtr(ptr, idx2) && isSamePtr(idx, ptr2)) {
 			break
 		}
@@ -10684,9 +10660,8 @@ func rewriteValueARM64_OpARM64MOVHloadidx2(v *Value) bool {
 		if v_2.Op != OpARM64MOVHstorezeroidx2 {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2)) {
 			break
 		}
@@ -10705,7 +10680,6 @@ func rewriteValueARM64_OpARM64MOVHreg(v *Value) bool {
 		if x.Op != OpARM64MOVBload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10717,7 +10691,6 @@ func rewriteValueARM64_OpARM64MOVHreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10729,7 +10702,6 @@ func rewriteValueARM64_OpARM64MOVHreg(v *Value) bool {
 		if x.Op != OpARM64MOVHload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10741,7 +10713,6 @@ func rewriteValueARM64_OpARM64MOVHreg(v *Value) bool {
 		if x.Op != OpARM64MOVBloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10753,7 +10724,6 @@ func rewriteValueARM64_OpARM64MOVHreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10765,7 +10735,6 @@ func rewriteValueARM64_OpARM64MOVHreg(v *Value) bool {
 		if x.Op != OpARM64MOVHloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -10777,7 +10746,6 @@ func rewriteValueARM64_OpARM64MOVHreg(v *Value) bool {
 		if x.Op != OpARM64MOVHloadidx2 {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12086,11 +12054,10 @@ func rewriteValueARM64_OpARM64MOVWUload(v *Value) bool {
 		if v_1.Op != OpARM64FMOVSstore || v_1.AuxInt != off || v_1.Aux != sym {
 			break
 		}
-		_ = v_1.Args[2]
+		val := v_1.Args[1]
 		if ptr != v_1.Args[0] {
 			break
 		}
-		val := v_1.Args[1]
 		v.reset(OpARM64FMOVSfpgp)
 		v.AddArg(val)
 		return true
@@ -12188,7 +12155,6 @@ func rewriteValueARM64_OpARM64MOVWUload(v *Value) bool {
 		}
 		off2 := v_1.AuxInt
 		sym2 := v_1.Aux
-		_ = v_1.Args[1]
 		ptr2 := v_1.Args[0]
 		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
 			break
@@ -12279,9 +12245,8 @@ func rewriteValueARM64_OpARM64MOVWUloadidx(v *Value) bool {
 		if v_2.Op != OpARM64MOVWstorezeroidx {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2) || isSamePtr(ptr, idx2) && isSamePtr(idx, ptr2)) {
 			break
 		}
@@ -12318,9 +12283,8 @@ func rewriteValueARM64_OpARM64MOVWUloadidx4(v *Value) bool {
 		if v_2.Op != OpARM64MOVWstorezeroidx4 {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2)) {
 			break
 		}
@@ -12339,7 +12303,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12351,7 +12314,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12363,7 +12325,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVWUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12375,7 +12336,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12387,7 +12347,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12399,7 +12358,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVWUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12411,7 +12369,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUloadidx2 {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12423,7 +12380,6 @@ func rewriteValueARM64_OpARM64MOVWUreg(v *Value) bool {
 		if x.Op != OpARM64MOVWUloadidx4 {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12619,7 +12575,6 @@ func rewriteValueARM64_OpARM64MOVWload(v *Value) bool {
 		}
 		off2 := v_1.AuxInt
 		sym2 := v_1.Aux
-		_ = v_1.Args[1]
 		ptr2 := v_1.Args[0]
 		if !(sym == sym2 && off == off2 && isSamePtr(ptr, ptr2)) {
 			break
@@ -12697,9 +12652,8 @@ func rewriteValueARM64_OpARM64MOVWloadidx(v *Value) bool {
 		if v_2.Op != OpARM64MOVWstorezeroidx {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2) || isSamePtr(ptr, idx2) && isSamePtr(idx, ptr2)) {
 			break
 		}
@@ -12736,9 +12690,8 @@ func rewriteValueARM64_OpARM64MOVWloadidx4(v *Value) bool {
 		if v_2.Op != OpARM64MOVWstorezeroidx4 {
 			break
 		}
-		_ = v_2.Args[2]
-		ptr2 := v_2.Args[0]
 		idx2 := v_2.Args[1]
+		ptr2 := v_2.Args[0]
 		if !(isSamePtr(ptr, ptr2) && isSamePtr(idx, idx2)) {
 			break
 		}
@@ -12757,7 +12710,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVBload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12769,7 +12721,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12781,7 +12732,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVHload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12793,7 +12743,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12805,7 +12754,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVWload {
 			break
 		}
-		_ = x.Args[1]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12817,7 +12765,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVBloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12829,7 +12776,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVBUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12841,7 +12787,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVHloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12853,7 +12798,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12865,7 +12809,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVWloadidx {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12877,7 +12820,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVHloadidx2 {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12889,7 +12831,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVHUloadidx2 {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true
@@ -12901,7 +12842,6 @@ func rewriteValueARM64_OpARM64MOVWreg(v *Value) bool {
 		if x.Op != OpARM64MOVWloadidx4 {
 			break
 		}
-		_ = x.Args[2]
 		v.reset(OpARM64MOVDreg)
 		v.AddArg(x)
 		return true