[llvm] [LLVM][InstCombine] Preserve vector types when shrinking FP constants. (PR #163598)

[Paul Walker via llvm-commits]

================
@@ -1643,33 +1643,43 @@ Instruction *InstCombinerImpl::visitSExt(SExtInst &Sext) {
 
 /// Return a Constant* for the specified floating-point constant if it fits
 /// in the specified FP type without changing its value.
-static bool fitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) {
+static bool fitsInFPType(APFloat F, const fltSemantics &Sem) {
   bool losesInfo;
-  APFloat F = CFP->getValueAPF();
   (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo);
   return !losesInfo;
 }
 
-static Type *shrinkFPConstant(ConstantFP *CFP, bool PreferBFloat) {
-  if (CFP->getType() == Type::getPPC_FP128Ty(CFP->getContext()))
-    return nullptr;  // No constant folding of this.
+static Type *shrinkFPConstant(LLVMContext &Ctx, APFloat F, bool PreferBFloat) {
   // See if the value can be truncated to bfloat and then reextended.
-  if (PreferBFloat && fitsInFPType(CFP, APFloat::BFloat()))
-    return Type::getBFloatTy(CFP->getContext());
+  if (PreferBFloat && fitsInFPType(F, APFloat::BFloat()))
+    return Type::getBFloatTy(Ctx);
   // See if the value can be truncated to half and then reextended.
-  if (!PreferBFloat && fitsInFPType(CFP, APFloat::IEEEhalf()))
-    return Type::getHalfTy(CFP->getContext());
+  if (!PreferBFloat && fitsInFPType(F, APFloat::IEEEhalf()))
+    return Type::getHalfTy(Ctx);
   // See if the value can be truncated to float and then reextended.
-  if (fitsInFPType(CFP, APFloat::IEEEsingle()))
-    return Type::getFloatTy(CFP->getContext());
-  if (CFP->getType()->isDoubleTy())
-    return nullptr;  // Won't shrink.
-  if (fitsInFPType(CFP, APFloat::IEEEdouble()))
-    return Type::getDoubleTy(CFP->getContext());
-  // Don't try to shrink to various long double types.
+  if (fitsInFPType(F, APFloat::IEEEsingle()))
+    return Type::getFloatTy(Ctx);
+  // See if the value can be truncated to double and then reextended.
+  if (fitsInFPType(F, APFloat::IEEEdouble()))
+    return Type::getDoubleTy(Ctx);
+  // Does not shrink.
   return nullptr;
 }
 
+static Type *shrinkFPConstant(ConstantFP *CFP, bool PreferBFloat) {
+  Type *Ty = CFP->getType();
+  if (Ty->getScalarType() == Type::getPPC_FP128Ty(CFP->getContext()))
+    return nullptr; // No constant folding of this.
+
+  Type *ShrinkTy =
+      shrinkFPConstant(CFP->getContext(), CFP->getValueAPF(), PreferBFloat);
+  if (auto *VecTy = dyn_cast<VectorType>(Ty))
+    ShrinkTy = VectorType::get(ShrinkTy, VecTy);
+
+  // Does it shrink?
+  return ShrinkTy != Ty ? ShrinkTy : nullptr;
----------------
paulwalker-arm wrote:

I wasn't sure if `getSemantics() == APFloat::IEEEdouble()` is equivalent to `CFP->getType()->isDoubleTy()`.  Sounds like you're saying it is?

https://github.com/llvm/llvm-project/pull/163598