cmd/compile: correct code generation for right shifts on riscv64

The code generation on riscv64 will currently result in incorrect
assembly when a 32 bit integer is right shifted by an amount that
exceeds the size of the type. In particular, this occurs when an
int32 or uint32 is cast to a 64 bit type and right shifted by a
value larger than 31.

Fix this by moving the SRAW/SRLW conversion into the right shift
rules and removing the SignExt32to64/ZeroExt32to64. Add additional
rules that rewrite to SRAIW/SRLIW when the shift is less than the
size of the type, or replace/eliminate the shift when it exceeds
the size of the type.

Add SSA tests that would have caught this issue. Also add additional
codegen tests to ensure that the resulting assembly is what we
expect in these overflow cases.

Fixes #64285

Change-Id: Ie97b05668597cfcb91413afefaab18ee1aa145ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/545035
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: M Zhuo <mzh@golangcn.org>
Reviewed-by: Mark Ryan <markdryan@rivosinc.com>
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/test/codegen/shift.go b/test/codegen/shift.go
index 32cfaffae0..50d60426d0 100644
--- a/test/codegen/shift.go
+++ b/test/codegen/shift.go
@@ -22,12 +22,42 @@ func rshConst64Ux64(v uint64) uint64 {
 	return v >> uint64(33)
 }
 
+func rshConst64Ux64Overflow32(v uint32) uint64 {
+	// riscv64:"MOV\t\\$0,",-"SRL"
+	return uint64(v) >> 32
+}
+
+func rshConst64Ux64Overflow16(v uint16) uint64 {
+	// riscv64:"MOV\t\\$0,",-"SRL"
+	return uint64(v) >> 16
+}
+
+func rshConst64Ux64Overflow8(v uint8) uint64 {
+	// riscv64:"MOV\t\\$0,",-"SRL"
+	return uint64(v) >> 8
+}
+
 func rshConst64x64(v int64) int64 {
 	// ppc64x:"SRAD"
 	// riscv64:"SRAI\t",-"OR",-"SLTIU"
 	return v >> uint64(33)
 }
 
+func rshConst64x64Overflow32(v int32) int64 {
+	// riscv64:"SRAIW",-"SLLI",-"SRAI\t"
+	return int64(v) >> 32
+}
+
+func rshConst64x64Overflow16(v int16) int64 {
+	// riscv64:"SLLI","SRAI",-"SRAIW"
+	return int64(v) >> 16
+}
+
+func rshConst64x64Overflow8(v int8) int64 {
+	// riscv64:"SLLI","SRAI",-"SRAIW"
+	return int64(v) >> 8
+}
+
 func lshConst32x64(v int32) int32 {
 	// ppc64x:"SLW"
 	// riscv64:"SLLI",-"AND",-"SLTIU", -"MOVW"