diff --git a/src/cmd/compile/internal/ssa/known_bits.go b/src/cmd/compile/internal/ssa/known_bits.go
index 693e494219e82f..063586a6d06573 100644
--- a/src/cmd/compile/internal/ssa/known_bits.go
+++ b/src/cmd/compile/internal/ssa/known_bits.go
@@ -45,6 +45,7 @@ func KnownBits(f *Func) {
 			}
 			val, k := kb.fold(v)
 			if k != -1 {
+				kb.simplifyValue(v)
 				continue
 			}
 			if f.Pass.Debug > 0 {
@@ -273,6 +274,43 @@ func (kb *knownBitsState) fold(v *Value) (value, known int64) {
 	}
 }
 
+func (kb *knownBitsState) simplifyValue(v *Value) {
+	switch v.Op {
+	case ssaop.OpAnd64, ssaop.OpAnd32, ssaop.OpAnd16, ssaop.OpAnd8:
+		x, xk := kb.fold(v.Args[0])
+		y, yk := kb.fold(v.Args[1])
+		for i := range 2 {
+			xAllCouldBeOnes := x | ^xk
+			yAllCouldBeZeros := ^y
+			if xAllCouldBeOnes&yAllCouldBeZeros == 0 {
+				if f := v.Block.Func; f.Pass.Debug > 0 {
+					f.Warnl(v.Pos, "Removed %v no-op %v", v, v.Op)
+				}
+				v.CopyOf(v.Args[i])
+				return
+			}
+			x, y = y, x
+			xk, yk = yk, xk
+		}
+	case ssaop.OpOr64, ssaop.OpOr32, ssaop.OpOr16, ssaop.OpOr8:
+		x, xk := kb.fold(v.Args[0])
+		y, yk := kb.fold(v.Args[1])
+		for i := range 2 {
+			xAllCouldBeZeros := ^x
+			yAllCouldBeOnes := y | ^yk
+			if xAllCouldBeZeros&yAllCouldBeOnes == 0 {
+				if f := v.Block.Func; f.Pass.Debug > 0 {
+					f.Warnl(v.Pos, "Removed %v no-op %v", v, v.Op)
+				}
+				v.CopyOf(v.Args[i])
+				return
+			}
+			x, y = y, x
+			xk, yk = yk, xk
+		}
+	}
+}
+
 func (kbe knownBitsEntry) String() string {
 	lut := []rune{ // indexed by knownBit<<1 | valueBit
 		0b00: '?',
diff --git a/src/cmd/go/testdata/script/cover_atomic_pkgall.txt b/src/cmd/go/testdata/script/cover_atomic_pkgall.txt
index 8f4397b4602de3..ad2093b7ad83c6 100644
--- a/src/cmd/go/testdata/script/cover_atomic_pkgall.txt
+++ b/src/cmd/go/testdata/script/cover_atomic_pkgall.txt
@@ -7,6 +7,8 @@ stdout ok[\s\S]+?coverage
 
 [!race] stop
 
+[GOARCH:loong64] skip 'broken on loong64: #78219'
+
 go test -coverpkg=all -race x
 stdout ok[\s\S]+?coverage
 
diff --git a/src/cmd/go/testdata/script/cover_pkgall_runtime.txt b/src/cmd/go/testdata/script/cover_pkgall_runtime.txt
index f92df35f636c01..600941b315c716 100644
--- a/src/cmd/go/testdata/script/cover_pkgall_runtime.txt
+++ b/src/cmd/go/testdata/script/cover_pkgall_runtime.txt
@@ -7,6 +7,8 @@ stdout ok[\s\S]+?coverage
 
 [!race] stop
 
+[GOARCH:loong64] skip 'broken on loong64: #78219'
+
 go test -coverpkg=all -race x
 stdout ok[\s\S]+?coverage
 
diff --git a/src/cmd/go/testdata/script/cover_test_race_issue56370.txt b/src/cmd/go/testdata/script/cover_test_race_issue56370.txt
index a18c2a7a41c870..94b2ea05d3cae9 100644
--- a/src/cmd/go/testdata/script/cover_test_race_issue56370.txt
+++ b/src/cmd/go/testdata/script/cover_test_race_issue56370.txt
@@ -1,5 +1,7 @@
 [!race] skip
 
+[GOARCH:loong64] skip 'broken on loong64: #78219'
+
 go test -race -cover issue.56370/filter
 
 -- go.mod --
diff --git a/src/cmd/go/testdata/script/test_race.txt b/src/cmd/go/testdata/script/test_race.txt
index c42f494bd84328..948c45105ea8b6 100644
--- a/src/cmd/go/testdata/script/test_race.txt
+++ b/src/cmd/go/testdata/script/test_race.txt
@@ -2,6 +2,8 @@
 
 go test testrace
 
+[GOARCH:loong64] skip 'broken on loong64: #78219'
+
 ! go test -race testrace
 stdout 'FAIL: TestRace'
 ! stdout 'PASS'
diff --git a/src/cmd/go/testdata/script/test_race_issue26995.txt b/src/cmd/go/testdata/script/test_race_issue26995.txt
index f979facd7e16eb..a19da4b892220a 100644
--- a/src/cmd/go/testdata/script/test_race_issue26995.txt
+++ b/src/cmd/go/testdata/script/test_race_issue26995.txt
@@ -1,5 +1,7 @@
 [!race] skip
 
+[GOARCH:loong64] skip 'broken on loong64: #78219'
+
 go test -v -race
 stdout 'testing_test.go:26: directCall'
 stdout 'testing_test.go:27: interfaceTBCall'
diff --git a/src/cmd/go/testdata/script/testing_issue40908.txt b/src/cmd/go/testdata/script/testing_issue40908.txt
index 70122cdb8c8b33..8f744a89fc9986 100644
--- a/src/cmd/go/testdata/script/testing_issue40908.txt
+++ b/src/cmd/go/testdata/script/testing_issue40908.txt
@@ -1,5 +1,7 @@
 [!race] skip
 
+[GOARCH:loong64] skip 'broken on loong64: #78219'
+
 go test -race testrace
 
 -- go.mod --
diff --git a/test/known_bits.go b/test/known_bits.go
index 5d6f2bdb203507..5de802ee9e00bf 100644
--- a/test/known_bits.go
+++ b/test/known_bits.go
@@ -429,3 +429,47 @@ func unknownBitsSextAfterTrunc(x int64, cond1, cond2 bool) int64 {
 
 	return int64(truncated) & (-1 << 63)
 }
+
+func pruneNoopAnd(x, y uint8) uint8 {
+	//    x & y => is x &= y a noop ?
+	// 1. 0 & 0 => noop
+	// 2. 1 & 0 => keep and
+	// 3. ? & 0 => keep and
+	// 4. 0 & 1 => noop
+	// 5. 1 & 1 => noop
+	// 6. ? & 1 => noop
+	// 7. 0 & ? => noop; can't be handled by prove
+	// 8. 1 & ? => keep and
+	// 9. ? & ? => keep and
+
+	// Test patterns: 76541
+	x &= 0b01000
+	x |= 0b00100
+	y &= 0b10000
+	y |= 0b01110
+
+	return x & y // ERROR "Removed v[0-9]+ no-op And8$"
+}
+
+func pruneNoopOr(x, y uint8) uint8 {
+	//    x | y => is x |= y a noop ?
+	// 1. 0 | 0 => noop
+	// 2. 1 | 0 => noop
+	// 3. ? | 0 => noop
+	// 4. 0 | 1 => keep or
+	// 5. 1 | 1 => noop
+	// 6. ? | 1 => keep or
+	// 7. 0 | ? => keep or
+	// 8. 1 | ? => noop; can't be handled by prove
+	// 9. ? | ? => keep or
+
+	// Test patterns: 85321
+	// invert the and & or in setup otherwise generic.rules reassociate in a
+	// form known bits doesn't for.
+	x |= 0b11010
+	x &= 0b11110
+	y |= 0b01000
+	y &= 0b11000
+
+	return x | y // ERROR "Removed v[0-9]+ no-op Or8$"
+}