Translate llvm.maxnum intrinsic function (#2299)

Map to fmax SPIR-V instruction from OpenCL extended instruction set.

Cherry-pick of KhronosGroup/SPIRV-LLVM-Translator@380c429.

Author: bader

llvm-spirv/lib/SPIRV/SPIRVUtil.cpp

@@ -1509,7 +1509,8 @@ bool hasLoopMetadata(const Module *M) {
 bool checkTypeForSPIRVExtendedInstLowering(IntrinsicInst *II, SPIRVModule *BM) {
   switch (II->getIntrinsicID()) {
   case Intrinsic::fabs:
-  case Intrinsic::ceil: {
+  case Intrinsic::ceil:
+  case Intrinsic::maxnum: {
     Type *Ty = II->getType();
     if (II->getArgOperand(0)->getType() != Ty)
       return false;

llvm-spirv/lib/SPIRV/SPIRVWriter.cpp

@@ -2041,6 +2041,16 @@ SPIRVValue *LLVMToSPIRV::transIntrinsicInst(IntrinsicInst *II,
     return BM->addBinaryInst(OpFAdd, Ty, Mul,
                              transValue(II->getArgOperand(2), BB), BB);
   }
+  case Intrinsic::maxnum: {
+    if (!checkTypeForSPIRVExtendedInstLowering(II, BM))
+      break;
+    SPIRVWord ExtOp = OpenCLLIB::Fmax;
+    SPIRVType *STy = transType(II->getType());
+    std::vector<SPIRVValue *> Ops{transValue(II->getArgOperand(0), BB),
+                                  transValue(II->getArgOperand(1), BB)};
+    return BM->addExtInst(STy, BM->getExtInstSetId(SPIRVEIS_OpenCL), ExtOp, Ops,
+                          BB);
+  }
   case Intrinsic::usub_sat: {
     // usub.sat(a, b) -> (a > b) ? a - b : 0
     SPIRVType *Ty = transType(II->getType());

llvm-spirv/test/maxnum.ll

@@ -0,0 +1,21 @@
+; RUN: llvm-as %s -o %t.bc
+; RUN: llvm-spirv %t.bc -spirv-text -o - | FileCheck %s
+; RUN: llvm-spirv %t.bc -o %t.spv
+; RUN: spirv-val %t.spv
+
+target datalayout = "e-i64:64-v16:16-v24:32-v32:32-v48:64-v96:128-v192:256-v256:256-v512:512-v1024:1024"
+target triple = "spir64-unknown-unknown"
+
+define spir_func float @Test(float %x, float %y) {
+entry:
+  %0 = call float @llvm.maxnum.f32(float %x, float %y)
+  ret float %0
+}
+
+; CHECK: Function
+; CHECK: FunctionParameter {{[0-9]+}} [[x:[0-9]+]]
+; CHECK: FunctionParameter {{[0-9]+}} [[y:[0-9]+]]
+; CHECK: ExtInst {{[0-9]+}} [[res:[0-9]+]] {{[0-9]+}} fmax [[x]] [[y]]
+; CHECK: ReturnValue [[res]]
+
+declare float @llvm.maxnum.f32(float, float)