[llvm] [llvm][AMDGPU] Implemented isProfitableToHoist and isFMAFasterThanFMulAndFAdd (PR #108756)

[Matt Arsenault via llvm-commits]

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@@ -1000,6 +1031,33 @@ bool AMDGPUTargetLowering::isTruncateFree(Type *Source, Type *Dest) const {
   return DestSize < SrcSize && DestSize % 32 == 0;
 }
 
+/// Check if it is profitable to hoist instruction in then/else to if.
+/// Not profitable if I and it's user can form a FMA instruction
+/// because we prefer FMSUB/FMADD.
+bool AMDGPUTargetLowering::isProfitableToHoist(Instruction *I) const {
+  if (I->getOpcode() != Instruction::FMul)
+    return true;
+
+  if (!I->hasOneUse())
+    return true;
+
+  Instruction *User = I->user_back();
+
+  if (!(User->getOpcode() == Instruction::FSub ||
+        User->getOpcode() == Instruction::FAdd))
+    return true;
+
+  const TargetOptions &Options = getTargetMachine().Options;
+  const Function *F = I->getFunction();
+  const DataLayout &DL = F->getDataLayout();
+  Type *Ty = User->getOperand(0)->getType();
+
+  return !(
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arsenm wrote:

Same, demorgan this. Should also check legality first 

https://github.com/llvm/llvm-project/pull/108756