cmd/compile: mask SLL,SRL,SRAconst shift amount

mips SRA/SLL/SRL shift amounts are used mod 32; this change aligns the
XXXconst rules to mask the shift amount by &31.

Passes

  $ GOARCH=mips go build -toolexec 'toolstash -cmp' -a std
  $ GOARCH=mipsle go build -toolexec 'toolstash -cmp' -a std

Fixes #42587

Change-Id: I6003ebd0bc500fba4cf6fb10254e1b557bf8c48f
Reviewed-on: https://go-review.googlesource.com/c/go/+/270117
Trust: Alberto Donizetti <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

Author: ALTree

src/cmd/compile/internal/ssa/gen/MIPS.rules

@@ -567,10 +567,9 @@
 (XOR x (MOVWconst [c])) => (XORconst [c] x)
 (NOR x (MOVWconst [c])) => (NORconst [c] x)
 
-(SRA x (MOVWconst [c])) && c >= 32 => (SRAconst x [31])
-(SLL x (MOVWconst [c])) => (SLLconst x [c])
-(SRL x (MOVWconst [c])) => (SRLconst x [c])
-(SRA x (MOVWconst [c])) => (SRAconst x [c])
+(SLL x (MOVWconst [c])) => (SLLconst x [c&31])
+(SRL x (MOVWconst [c])) => (SRLconst x [c&31])
+(SRA x (MOVWconst [c])) => (SRAconst x [c&31])
 
 (SGT  (MOVWconst [c]) x) => (SGTconst  [c] x)
 (SGTU (MOVWconst [c]) x) => (SGTUconst [c] x)

src/cmd/compile/internal/ssa/gen/MIPSOps.go

@@ -185,11 +185,11 @@ func init() {
 
 		// shifts
 		{name: "SLL", argLength: 2, reg: gp21, asm: "SLL"},                    // arg0 << arg1, shift amount is mod 32
-		{name: "SLLconst", argLength: 1, reg: gp11, asm: "SLL", aux: "Int32"}, // arg0 << auxInt
+		{name: "SLLconst", argLength: 1, reg: gp11, asm: "SLL", aux: "Int32"}, // arg0 << auxInt, shift amount must be 0 through 31 inclusive
 		{name: "SRL", argLength: 2, reg: gp21, asm: "SRL"},                    // arg0 >> arg1, unsigned, shift amount is mod 32
-		{name: "SRLconst", argLength: 1, reg: gp11, asm: "SRL", aux: "Int32"}, // arg0 >> auxInt, unsigned
+		{name: "SRLconst", argLength: 1, reg: gp11, asm: "SRL", aux: "Int32"}, // arg0 >> auxInt, shift amount must be 0 through 31 inclusive
 		{name: "SRA", argLength: 2, reg: gp21, asm: "SRA"},                    // arg0 >> arg1, signed, shift amount is mod 32
-		{name: "SRAconst", argLength: 1, reg: gp11, asm: "SRA", aux: "Int32"}, // arg0 >> auxInt, signed
+		{name: "SRAconst", argLength: 1, reg: gp11, asm: "SRA", aux: "Int32"}, // arg0 >> auxInt, signed, shift amount must be 0 through 31 inclusive
 
 		{name: "CLZ", argLength: 1, reg: gp11, asm: "CLZ"},
 

src/cmd/compile/internal/ssa/rewriteMIPS.go

@@ -0,0 +1,15 @@
+// compile
+
+// Copyright 2020 The Go Authors. All rights reserved.  Use of this
+// source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package p
+
+func f() {
+	var i, j int
+	_ = func() {
+		i = 32
+		j = j>>i | len([]int{})
+	}
+}