[Review] set FPFastMathDefault equal to 0 for every entry-point

Author: jmmartinez

lib/SPIRV/SPIRVWriter.cpp

@@ -6583,10 +6583,45 @@ bool LLVMToSPIRVBase::transExecutionMode() {
   }
 
   transFPContract();
+  transFPFastMathDefault();
 
   return true;
 }
 
+void LLVMToSPIRVBase::transFPFastMathDefault() {
+  if (!BM->hasCapability(CapabilityFloatControls2))
+    return;
+
+  SmallVector<SPIRVType *> AllFPTypes;
+  for (auto [_, SPVTy] : TypeMap) {
+    if (!SPVTy->isTypeFloat())
+      continue;
+    AllFPTypes.push_back(SPVTy);
+  }
+
+  // We encode an fp-operaiton with no FPFastMathMode flags set as an
+  // fp-operation with all the flags set to 0. Instead of setting the flag for
+  // every individual operation, we set it once, for the entry-point.
+  SPIRVConstant *AllFlagsZero = BM->getLiteralAsConstant(0);
+  for (Function &F : *M) {
+    SPIRVValue *TranslatedF = getTranslatedValue(&F);
+    if (!TranslatedF)
+      continue;
+
+    SPIRVFunction *BF = static_cast<SPIRVFunction *>(TranslatedF);
+    bool IsKernelEntryPoint =
+        BM->isEntryPoint(spv::ExecutionModelKernel, BF->getId());
+    if (!IsKernelEntryPoint)
+      continue;
+
+    for (SPIRVType *FPTy : AllFPTypes) {
+      BF->addExecutionMode(
+          new SPIRVExecutionModeId(BF, spv::ExecutionModeFPFastMathDefault,
+                                   FPTy->getId(), AllFlagsZero->getId()));
+    }
+  }
+}
+
 void LLVMToSPIRVBase::transFPContract() {
   // SPV_KHR_float_controls2 deprecates ContractionOff.
   if (BM->hasCapability(CapabilityFloatControls2))

lib/SPIRV/SPIRVWriter.h

@@ -148,6 +148,7 @@ class LLVMToSPIRVBase : protected BuiltinCallHelper {
   bool translate();
   bool transExecutionMode();
   void transFPContract();
+  void transFPFastMathDefault();
   SPIRVValue *transConstant(Value *V);
   /// Translate a reference to a constant in a constant expression. This may
   /// involve inserting extra bitcasts to correct type issues.

lib/SPIRV/libSPIRV/SPIRVEntry.h

@@ -668,6 +668,15 @@ class SPIRVExecutionMode : public SPIRVAnnotation {
     WordLiterals.push_back(Z);
     updateModuleVersion();
   }
+  // Complete constructor for FPFastMathDefault
+  SPIRVExecutionMode(Op OC, SPIRVEntry *TheTarget,
+                     SPIRVExecutionModeKind TheExecMode, SPIRVWord X,
+                     SPIRVWord Y)
+      : SPIRVAnnotation(OC, TheTarget, 5), ExecMode(TheExecMode) {
+    WordLiterals.push_back(X);
+    WordLiterals.push_back(Y);
+    updateModuleVersion();
+  }
   // Complete constructor for VecTypeHint, SubgroupSize, SubgroupsPerWorkgroup
   SPIRVExecutionMode(Op OC, SPIRVEntry *TheTarget,
                      SPIRVExecutionModeKind TheExecMode, SPIRVWord Code)
@@ -728,6 +737,13 @@ class SPIRVExecutionModeId : public SPIRVExecutionMode {
       : SPIRVExecutionMode(OpExecutionModeId, TheTarget, TheExecMode, X, Y, Z) {
     updateModuleVersion();
   }
+  // Complete constructor for FPFastMathDefault
+  SPIRVExecutionModeId(SPIRVEntry *TheTarget,
+                       SPIRVExecutionModeKind TheExecMode, SPIRVWord X,
+                       SPIRVWord Y)
+      : SPIRVExecutionMode(OpExecutionModeId, TheTarget, TheExecMode, X, Y) {
+    updateModuleVersion();
+  }
   // Complete constructor for SubgroupsPerWorkgroupId
   SPIRVExecutionModeId(SPIRVEntry *TheTarget,
                        SPIRVExecutionModeKind TheExecMode, SPIRVWord Code)