String Compression for MIPS32 and MIPS64
Changes on intrinsics and Code Generation on MIPS32 and MIPS64 for
string compression feature.
Testing is done with STRING_COMPRESSION_ENABLED = true (in libcore),
mirror::kUseStringCompression = true and STRING_COMPRESSION_FEATURE set
to 1.
Test: booted MIPS32 and MIPS64 in QEMU
Test: mma test-art-target-run-test on CI20 (MIPS32R2)
Test: mma test-art-target-run-test in QEMU (MIPS64R6)
Change-Id: If50a6b6c0792bfa34d4fdff6bf2c7542211d2689
diff --git a/compiler/optimizing/intrinsics_mips.cc b/compiler/optimizing/intrinsics_mips.cc
index 6cf9b83..64a6840 100644
--- a/compiler/optimizing/intrinsics_mips.cc
+++ b/compiler/optimizing/intrinsics_mips.cc
@@ -2004,31 +2004,48 @@
__ Lw(temp2, arg, class_offset);
__ Bne(temp1, temp2, &return_false);
- // Load lengths of this and argument strings.
+ // Load `count` fields of this and argument strings.
__ Lw(temp1, str, count_offset);
__ Lw(temp2, arg, count_offset);
- // Check if lengths are equal, return false if they're not.
+ // Check if `count` fields are equal, return false if they're not.
+ // Also compares the compression style, if differs return false.
__ Bne(temp1, temp2, &return_false);
- // Return true if both strings are empty.
+ // Return true if both strings are empty. Even with string compression `count == 0` means empty.
+ static_assert(static_cast<uint32_t>(mirror::StringCompressionFlag::kCompressed) == 0u,
+ "Expecting 0=compressed, 1=uncompressed");
__ Beqz(temp1, &return_true);
// Don't overwrite input registers
__ Move(TMP, str);
__ Move(temp3, arg);
- // Assertions that must hold in order to compare strings 2 characters at a time.
+ // Assertions that must hold in order to compare strings 4 bytes at a time.
DCHECK_ALIGNED(value_offset, 4);
static_assert(IsAligned<4>(kObjectAlignment), "String of odd length is not zero padded");
- // Loop to compare strings 2 characters at a time starting at the beginning of the string.
- // Ok to do this because strings are zero-padded.
+ // For string compression, calculate the number of bytes to compare (not chars).
+ if (mirror::kUseStringCompression) {
+ // Extract compression flag.
+ if (IsR2OrNewer()) {
+ __ Ext(temp2, temp1, 0, 1);
+ } else {
+ __ Sll(temp2, temp1, 31);
+ __ Srl(temp2, temp2, 31);
+ }
+ __ Srl(temp1, temp1, 1); // Extract length.
+ __ Sllv(temp1, temp1, temp2); // Double the byte count if uncompressed.
+ }
+
+ // Loop to compare strings 4 bytes at a time starting at the beginning of the string.
+ // Ok to do this because strings are zero-padded to kObjectAlignment.
__ Bind(&loop);
__ Lw(out, TMP, value_offset);
__ Lw(temp2, temp3, value_offset);
__ Bne(out, temp2, &return_false);
__ Addiu(TMP, TMP, 4);
__ Addiu(temp3, temp3, 4);
- __ Addiu(temp1, temp1, -2);
+ // With string compression, we have compared 4 bytes, otherwise 2 chars.
+ __ Addiu(temp1, temp1, mirror::kUseStringCompression ? -4 : -2);
__ Bgtz(temp1, &loop);
// Return true and exit the function.
@@ -2578,6 +2595,30 @@
__ Addu(dstPtr, dstPtr, AT);
}
+ if (mirror::kUseStringCompression) {
+ MipsLabel uncompressed_copy, compressed_loop;
+ const uint32_t count_offset = mirror::String::CountOffset().Uint32Value();
+ // Load count field and extract compression flag.
+ __ LoadFromOffset(kLoadWord, TMP, srcObj, count_offset);
+ __ Sll(TMP, TMP, 31);
+
+ // If string is uncompressed, use memcpy() path.
+ __ Bnez(TMP, &uncompressed_copy);
+
+ // Copy loop for compressed src, copying 1 character (8-bit) to (16-bit) at a time.
+ __ Addu(srcPtr, srcObj, srcBegin);
+ __ Bind(&compressed_loop);
+ __ LoadFromOffset(kLoadUnsignedByte, TMP, srcPtr, value_offset);
+ __ StoreToOffset(kStoreHalfword, TMP, dstPtr, 0);
+ __ Addiu(numChrs, numChrs, -1);
+ __ Addiu(srcPtr, srcPtr, 1);
+ __ Addiu(dstPtr, dstPtr, 2);
+ __ Bnez(numChrs, &compressed_loop);
+
+ __ B(&done);
+ __ Bind(&uncompressed_copy);
+ }
+
// Calculate source address.
__ Addiu(srcPtr, srcObj, value_offset);
if (IsR6()) {