[mips][FastISel] Implement bswap.

[vkalintiris]

Summary

Implement bswap intrinsic for MIPS FastISel. It's very different for MIPS32 R1/R2.

Based on a patch by Reed Kotler.

[rkotler]

Submit to commits list for comments too.

[dsanders]

test/CodeGen/Mips/Fast-ISel/bswap1.ll

14–15 ↗

(On Diff #18873)

Please use multiple FileCheck prefixes to handle things that are the same for both commands.

16 ↗

(On Diff #18873)

As mentioned in D6774, we can significantly simplify this using arguments and returns.

As noted there, I don't mind if this is part of the big cleanup.

50–51 ↗

(On Diff #18873)

It's possible to shave off one instruction here. At the moment this code is equivalent to this expression:

R = (X << 24) | (X >> 24) | ((X >> 8) & 0xFF00) | ((X << 8) & 0xFF0000)

The '& 0xFF0000' requires an lui+and but with a slight change to the expression we could use an andi instead:

R = (X << 24) | (X >> 24) | ((X >> 8) & 0xFF00) | ((X & 0xFF00) << 8)

66–103 ↗

(On Diff #18873)

Unnecessary

[vkalintiris]

Rebased, removed redundant instruction & cleaned up the tests.

[dsanders]

LGTM

llvm/trunk/lib/Target/Mips/MipsFastISel.cpp

bool MipsFastISel::fastLowerCall(CallLoweringInfo &CLI) {
   // Finish off the call including any return values.
   return finishCall(CLI, RetVT, NumBytes);
 }
 
 bool MipsFastISel::fastLowerIntrinsicCall(const IntrinsicInst *II) {
   switch (II->getIntrinsicID()) {
   default:
     return false;
+  case Intrinsic::bswap: {
+    Type *RetTy = II->getCalledFunction()->getReturnType();
+
+    MVT VT;
+    if (!isTypeSupported(RetTy, VT))
+      return false;
+
+    unsigned SrcReg = getRegForValue(II->getOperand(0));
+    if (SrcReg == 0)
+      return false;
+    unsigned DestReg = createResultReg(&Mips::GPR32RegClass);
+    if (DestReg == 0)
+      return false;
+    if (VT == MVT::i16) {
+      if (Subtarget->hasMips32r2()) {
+        emitInst(Mips::WSBH, DestReg).addReg(SrcReg);
+        updateValueMap(II, DestReg);
+        return true;
+      } else {
+        unsigned TempReg[3];
+        for (int i = 0; i < 3; i++) {
+          TempReg[i] = createResultReg(&Mips::GPR32RegClass);
+          if (TempReg[i] == 0)
+            return false;
+        }
+        emitInst(Mips::SLL, TempReg[0]).addReg(SrcReg).addImm(8);
+        emitInst(Mips::SRL, TempReg[1]).addReg(SrcReg).addImm(8);
+        emitInst(Mips::OR, TempReg[2]).addReg(TempReg[0]).addReg(TempReg[1]);
+        emitInst(Mips::ANDi, DestReg).addReg(TempReg[2]).addImm(0xFFFF);
+        updateValueMap(II, DestReg);
+        return true;
+      }
+    } else if (VT == MVT::i32) {
+      if (Subtarget->hasMips32r2()) {
+        unsigned TempReg = createResultReg(&Mips::GPR32RegClass);
+        emitInst(Mips::WSBH, TempReg).addReg(SrcReg);
+        emitInst(Mips::ROTR, DestReg).addReg(TempReg).addImm(16);
+        updateValueMap(II, DestReg);
+        return true;
+      } else {
+        unsigned TempReg[8];
+        for (int i = 0; i < 8; i++) {
+          TempReg[i] = createResultReg(&Mips::GPR32RegClass);
+          if (TempReg[i] == 0)
+            return false;
+        }
+
+        emitInst(Mips::SRL, TempReg[0]).addReg(SrcReg).addImm(8);
+        emitInst(Mips::SRL, TempReg[1]).addReg(SrcReg).addImm(24);
+        emitInst(Mips::ANDi, TempReg[2]).addReg(TempReg[0]).addImm(0xFF00);
+        emitInst(Mips::OR, TempReg[3]).addReg(TempReg[1]).addReg(TempReg[2]);
+
+        emitInst(Mips::ANDi, TempReg[4]).addReg(SrcReg).addImm(0xFF00);
+        emitInst(Mips::SLL, TempReg[5]).addReg(TempReg[4]).addImm(8);
+
+        emitInst(Mips::SLL, TempReg[6]).addReg(SrcReg).addImm(24);
+        emitInst(Mips::OR, TempReg[7]).addReg(TempReg[3]).addReg(TempReg[5]);
+        emitInst(Mips::OR, DestReg).addReg(TempReg[6]).addReg(TempReg[7]);
+        updateValueMap(II, DestReg);
+        return true;
+      }
+    }
+    return false;
+  }
   case Intrinsic::memcpy:
   case Intrinsic::memmove: {
     const auto *MTI = cast<MemTransferInst>(II);
     // Don't handle volatile.
     if (MTI->isVolatile())
       return false;
     if (!MTI->getLength()->getType()->isIntegerTy(32))
       return false;

llvm/trunk/test/CodeGen/Mips/Fast-ISel/bswap1.ll

+; RUN: llc < %s -march=mipsel -mcpu=mips32 -O0 -relocation-model=pic \
+; RUN:      -fast-isel=true -mips-fast-isel -fast-isel-abort=1 | FileCheck %s \
+; RUN:      -check-prefix=ALL -check-prefix=32R1
+; RUN: llc < %s -march=mipsel -mcpu=mips32r2 -O0 -relocation-model=pic \
+; RUN:      -fast-isel=true -mips-fast-isel -fast-isel-abort=1 | FileCheck %s \
+; RUN:      -check-prefix=ALL -check-prefix=32R2
+
+@a = global i16 -21829, align 2
+@b = global i32 -1430532899, align 4
+@a1 = common global i16 0, align 2
+@b1 = common global i32 0, align 4
+
+declare i16 @llvm.bswap.i16(i16)
+declare i32 @llvm.bswap.i32(i32)
+
+define void @b16() {
+  ; ALL-LABEL:  b16:
+
+  ; ALL:            lw    $[[A_ADDR:[0-9]+]], %got(a)($[[GOT_ADDR:[0-9]+]])
+  ; ALL:            lhu   $[[A_VAL:[0-9]+]], 0($[[A_ADDR]])
+
+  ; 32R1:           sll   $[[TMP1:[0-9]+]], $[[A_VAL]], 8
+  ; 32R1:           srl   $[[TMP2:[0-9]+]], $[[A_VAL]], 8
+  ; 32R1:           or    $[[TMP3:[0-9]+]], $[[TMP1]], $[[TMP2]]
+  ; 32R1:           andi  $[[TMP4:[0-9]+]], $[[TMP3]], 65535
+
+  ; 32R2:           wsbh  $[[RESULT:[0-9]+]], $[[A_VAL]]
+
+  %1 = load i16, i16* @a, align 2
+  %2 = call i16 @llvm.bswap.i16(i16 %1)
+  store i16 %2, i16* @a1, align 2
+  ret void
+}
+
+define void @b32() {
+  ; ALL-LABEL:  b32:
+
+  ; ALL:            lw    $[[B_ADDR:[0-9]+]], %got(b)($[[GOT_ADDR:[0-9]+]])
+  ; ALL:            lw    $[[B_VAL:[0-9]+]], 0($[[B_ADDR]])
+
+  ; 32R1:           srl   $[[TMP1:[0-9]+]], $[[B_VAL]], 8
+  ; 32R1:           srl   $[[TMP2:[0-9]+]], $[[B_VAL]], 24
+  ; 32R1:           andi  $[[TMP3:[0-9]+]], $[[TMP1]], 65280
+  ; 32R1:           or    $[[TMP4:[0-9]+]], $[[TMP2]], $[[TMP3]]
+  ; 32R1:           andi  $[[TMP5:[0-9]+]], $[[B_VAL]], 65280
+  ; 32R1:           sll   $[[TMP6:[0-9]+]], $[[TMP5]], 8
+  ; 32R1:           sll   $[[TMP7:[0-9]+]], $[[B_VAL]], 24
+  ; 32R1:           or    $[[TMP8:[0-9]+]], $[[TMP4]], $[[TMP6]]
+  ; 32R1:           or    $[[RESULT:[0-9]+]], $[[TMP7]], $[[TMP8]]
+
+  ; 32R2:           wsbh  $[[TMP:[0-9]+]], $[[B_VAL]]
+  ; 32R2:           rotr  $[[RESULT:[0-9]+]], $[[TMP]], 16
+
+  %1 = load i32, i32* @b, align 4
+  %2 = call i32 @llvm.bswap.i32(i32 %1)
+  store i32 %2, i32* @b1, align 4
+  ret void
+}