[llvm] [InstCombine] Make `(binop ({s|u}itofp),({s|u}itofp))` transform more flexible to mismatched signs (PR #84389)

[Nikita Popov via llvm-commits]

================
@@ -1406,41 +1406,27 @@ Value *InstCombinerImpl::dyn_castNegVal(Value *V) const {
 //        -> ({s|u}itofp (int_binop x, y))
 //    2) (fp_binop ({s|u}itofp x), FpC)
 //        -> ({s|u}itofp (int_binop x, (fpto{s|u}i FpC)))
-Instruction *InstCombinerImpl::foldFBinOpOfIntCasts(BinaryOperator &BO) {
-  Value *IntOps[2] = {nullptr, nullptr};
-  Constant *Op1FpC = nullptr;
-
-  // Check for:
-  //    1) (binop ({s|u}itofp x), ({s|u}itofp y))
-  //    2) (binop ({s|u}itofp x), FpC)
-  if (!match(BO.getOperand(0), m_SIToFP(m_Value(IntOps[0]))) &&
-      !match(BO.getOperand(0), m_UIToFP(m_Value(IntOps[0]))))
-    return nullptr;
-
-  if (!match(BO.getOperand(1), m_Constant(Op1FpC)) &&
-      !match(BO.getOperand(1), m_SIToFP(m_Value(IntOps[1]))) &&
-      !match(BO.getOperand(1), m_UIToFP(m_Value(IntOps[1]))))
-    return nullptr;
+//
+// Assuming the sign of the cast for x/y is `OpsFromSigned`.
+Instruction *InstCombinerImpl::foldFBinOpOfIntCastsFromSign(
+    BinaryOperator &BO, bool OpsFromSigned, std::array<Value *, 2> IntOps,
+    Constant *Op1FpC, SmallVectorImpl<WithCache<const Value *>> &OpsKnown) {
 
   Type *FPTy = BO.getType();
   Type *IntTy = IntOps[0]->getType();
 
-  // Do we have signed casts?
-  bool OpsFromSigned = isa<SIToFPInst>(BO.getOperand(0));
-
   unsigned IntSz = IntTy->getScalarSizeInBits();
   // This is the maximum number of inuse bits by the integer where the int -> fp
   // casts are exact.
   unsigned MaxRepresentableBits =
       APFloat::semanticsPrecision(FPTy->getScalarType()->getFltSemantics());
 
-  // Cache KnownBits a bit to potentially save some analysis.
-  WithCache<const Value *> OpsKnown[2] = {IntOps[0], IntOps[1]};
-
   // Preserve known number of leading bits. This can allow us to trivial nsw/nuw
   // checks later on.
   unsigned NumUsedLeadingBits[2] = {IntSz, IntSz};
 
+  // NB: This only comes up is OpsFromSigned is true, so there is no need to
+  // cache is between calls to `foldFBinOpOfIntCastsFromSign`.
----------------
nikic wrote:

```suggestion
  // cache it between calls to `foldFBinOpOfIntCastsFromSign`.
```

https://github.com/llvm/llvm-project/pull/84389