[Subzero][MIPS32] Implement sext, zext and trunc

src/IceTargetLoweringMIPS32.cpp

Index: src/IceTargetLoweringMIPS32.cpp
diff --git a/src/IceTargetLoweringMIPS32.cpp b/src/IceTargetLoweringMIPS32.cpp
index cbfad693619260aa00cd2b05f75316550c1e97d7..15b4f9b72c1872f37607ac8efbbd24599030d7fa 100644
--- a/src/IceTargetLoweringMIPS32.cpp
+++ b/src/IceTargetLoweringMIPS32.cpp
@@ -905,20 +905,85 @@ void TargetMIPS32::lowerCall(const InstCall *Instr) {
 
 void TargetMIPS32::lowerCast(const InstCast *Instr) {
   InstCast::OpKind CastKind = Instr->getCastKind();
+  Variable *Dest = Instr->getDest();
+  const Type DestTy = Dest->getType();
+  Operand *Src0 = legalizeUndef(Instr->getSrc(0));

[Jim Stichnoth, 2016/05/05 15:32:37]

Add this:
  const Type Src0Ty = Src0->getType();
and use it below in place of all the Src0->getType() calls.

[sagar.thakur, 2016/05/06 13:04:06]

Done.

+  if (isVectorType(DestTy) || Src0->getType() == IceType_i1) {
+    UnimplementedLoweringError(this, Instr);
+    return;
+  }
   switch (CastKind) {
   default:
     Func->setError("Cast type not supported");
     return;
   case InstCast::Sext: {
-    UnimplementedLoweringError(this, Instr);
+    if (DestTy == IceType_i64) {
+      auto *DestLo = llvm::cast<Variable>(loOperand(Dest));
+      auto *DestHi = llvm::cast<Variable>(hiOperand(Dest));
+      Variable *Src0R = legalizeToReg(Src0);
+      Variable *T_Lo = I32Reg();
+      if (Src0->getType() == IceType_i32) {
+        _mov(DestLo, Src0R);
+      } else if (Src0->getType() == IceType_i8) {
+        _sll(T_Lo, Src0R, 24);

[Jim Stichnoth, 2016/05/05 15:32:37]

I strongly prefer to avoid magic constants like 24 and 16.  Instead, something
like this:
  constexpr ShiftAmount = 32 - (CHAR_BIT * typeWidthInBytes(Src0Ty));
Sadly, that trades one magic constant for another, but I guess 32 could be a
static constexpr field in the TargetMIPS32 class.

[sagar.thakur, 2016/05/06 13:04:06]

Done.

+        _sra(DestLo, T_Lo, 24);
+      } else if (Src0->getType() == IceType_i16) {
+        _sll(T_Lo, Src0R, 16);
+        _sra(DestLo, T_Lo, 16);
+      }
+      _sra(DestHi, DestLo, 31);
+    } else {
+      Variable *Src0R = legalizeToReg(Src0);
+      Variable *T = makeReg(DestTy);
+      if (Src0->getType() == IceType_i8) {
+        _sll(T, Src0R, 24);
+        _sra(Dest, T, 24);
+      } else if (Src0->getType() == IceType_i16) {
+        _sll(T, Src0R, 16);
+        _sra(Dest, T, 16);
+      }
+    }
     break;
   }
   case InstCast::Zext: {
-    UnimplementedLoweringError(this, Instr);
+    if (DestTy == IceType_i64) {
+      auto *DestLo = llvm::cast<Variable>(loOperand(Dest));
+      auto *DestHi = llvm::cast<Variable>(hiOperand(Dest));
+      Variable *Src0R = legalizeToReg(Src0);
+
+      switch (Src0->getType()) {
+      default: { assert(Src0->getType() != IceType_i64); } break;
+      case IceType_i32: {
+        _mov(DestLo, Src0R);
+      } break;
+      case IceType_i16: {
+        _andi(DestLo, Src0R, 0xff);

[Jim Stichnoth, 2016/05/05 15:32:37]

Shouldn't the mask be 0xffff for i16 and 0xff for i8?

Also, similar to above, these masks could be constructed based on the type width
instead of "magic constants".

[sagar.thakur, 2016/05/06 13:04:06]

Done.

+      } break;
+      case IceType_i8: {
+        _andi(DestLo, Src0R, 0xffff);
+      } break;
+      }
+
+      auto *Zero = getZero();
+      _addiu(DestHi, Zero, 0);
+    } else {
+      Variable *Src0R = legalizeToReg(Src0);
+      Variable *T = makeReg(DestTy);
+      if (Src0->getType() == IceType_i8)
+        _andi(T, Src0R, 0xff);
+      else if (Src0->getType() == IceType_i16)
+        _andi(T, Src0R, 0xffff);
+      _mov(Dest, T);
+    }
     break;
   }
   case InstCast::Trunc: {
-    UnimplementedLoweringError(this, Instr);
+    if (Src0->getType() == IceType_i64)
+      Src0 = loOperand(Src0);
+    Variable *Src0R = legalizeToReg(Src0);
+    Variable *T = makeReg(DestTy);
+    _mov(T, Src0R);
+    _mov(Dest, T);
     break;
   }
   case InstCast::Fptrunc: