[llvm] [SPIRV] Add sign intrinsic part 1 (PR #101987)

[Farzon Lotfi via llvm-commits]

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@@ -1366,6 +1370,52 @@ bool SPIRVInstructionSelector::selectRsqrt(Register ResVReg,
       .constrainAllUses(TII, TRI, RBI);
 }
 
+bool SPIRVInstructionSelector::selectSign(Register ResVReg,
+                                          const SPIRVType *ResType,
+                                          MachineInstr &I) const {
+  assert(I.getNumOperands() == 3);
+  assert(I.getOperand(2).isReg());
+  MachineBasicBlock &BB = *I.getParent();
+  Register InputRegister = I.getOperand(2).getReg();
+  SPIRVType *InputType = GR.getSPIRVTypeForVReg(InputRegister);
+  auto &DL = I.getDebugLoc();
+
+  if (!InputType)
+    report_fatal_error("Input Type could not be determined.");
+
+  bool IsFloatTy = GR.isScalarOrVectorOfType(InputRegister, SPIRV::OpTypeFloat);
+
+  unsigned SignBitWidth = GR.getScalarOrVectorBitWidth(InputType);
+  unsigned ResBitWidth = GR.getScalarOrVectorBitWidth(ResType);
+
+  bool NeedsConversion = IsFloatTy || SignBitWidth != ResBitWidth;
+
+  auto SignOpcode = IsFloatTy ? GL::FSign : GL::SSign;
+  Register SignReg = NeedsConversion
+                         ? MRI->createVirtualRegister(&SPIRV::IDRegClass)
+                         : ResVReg;
+
+  bool Result =
+      BuildMI(BB, I, DL, TII.get(SPIRV::OpExtInst))
+          .addDef(SignReg)
+          .addUse(GR.getSPIRVTypeID(InputType))
+          .addImm(static_cast<uint32_t>(SPIRV::InstructionSet::GLSL_std_450))
+          .addImm(SignOpcode)
+          .addUse(InputRegister)
+          .constrainAllUses(TII, TRI, RBI);
+
+  if (NeedsConversion) {
+    auto ConvertOpcode = IsFloatTy ? SPIRV::OpConvertFToS : SPIRV::OpSConvert;
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farzonl wrote:

@Keenuts could you take a look  at this PR?  Also let me know what the right behavior should be for this `sign(double)` case?

https://github.com/llvm/llvm-project/pull/101987