[InstCombine] Refactoring matchFunnelShift (NFC)

[quic-eikansh]

The matchFunnelShift function was doing pattern matching and creating the fshl/fshr instruction if needed. Moved the pattern matching code to function convertShlOrLShrToFShlOrFShr. It can be reused for other optimizations.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: None (quic-eikansh)

Changes

The matchFunnelShift function was doing pattern matching and creating the fshl/fshr instruction if needed. Moved the pattern matching code to function convertShlOrLShrToFShlOrFShr. It can be reused for other optimizations.

---

Full diff: https://github.com/llvm/llvm-project/pull/73390.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+23-13)
• (modified) llvm/lib/Transforms/InstCombine/InstCombineInternal.h (+3)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 02881109f17d29f..fd4b416ec87922f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2706,9 +2706,8 @@ Instruction *InstCombinerImpl::matchBSwapOrBitReverse(Instruction &I,
   return LastInst;
 }
 
-/// Match UB-safe variants of the funnel shift intrinsic.
-static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
-                                     const DominatorTree &DT) {
+std::optional<std::tuple<Intrinsic::ID, SmallVector<Value *, 3>>>
+InstCombinerImpl::convertShlOrLShrToFShlOrFShr(Instruction &Or) {
   // TODO: Can we reduce the code duplication between this and the related
   // rotate matching code under visitSelect and visitTrunc?
   unsigned Width = Or.getType()->getScalarSizeInBits();
@@ -2716,7 +2715,7 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
   Instruction *Or0, *Or1;
   if (!match(Or.getOperand(0), m_Instruction(Or0)) ||
       !match(Or.getOperand(1), m_Instruction(Or1)))
-    return nullptr;
+    return std::nullopt;
 
   bool IsFshl = true; // Sub on LSHR.
   SmallVector<Value *, 3> FShiftArgs;
@@ -2730,7 +2729,7 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
         !match(Or1,
                m_OneUse(m_LogicalShift(m_Value(ShVal1), m_Value(ShAmt1)))) ||
         Or0->getOpcode() == Or1->getOpcode())
-      return nullptr;
+      return std::nullopt;
 
     // Canonicalize to or(shl(ShVal0, ShAmt0), lshr(ShVal1, ShAmt1)).
     if (Or0->getOpcode() == BinaryOperator::LShr) {
@@ -2766,7 +2765,7 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
       // might remove it after this fold). This still doesn't guarantee that the
       // final codegen will match this original pattern.
       if (match(R, m_OneUse(m_Sub(m_SpecificInt(Width), m_Specific(L))))) {
-        KnownBits KnownL = IC.computeKnownBits(L, /*Depth*/ 0, &Or);
+        KnownBits KnownL = computeKnownBits(L, /*Depth*/ 0, &Or);
         return KnownL.getMaxValue().ult(Width) ? L : nullptr;
       }
 
@@ -2810,7 +2809,7 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
       IsFshl = false; // Sub on SHL.
     }
     if (!ShAmt)
-      return nullptr;
+      return std::nullopt;
 
     FShiftArgs = {ShVal0, ShVal1, ShAmt};
   } else if (isa<ZExtInst>(Or0) || isa<ZExtInst>(Or1)) {
@@ -2832,18 +2831,18 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
     const APInt *ZextHighShlAmt;
     if (!match(Or0,
                m_OneUse(m_Shl(m_Value(ZextHigh), m_APInt(ZextHighShlAmt)))))
-      return nullptr;
+      return std::nullopt;
 
     if (!match(Or1, m_ZExt(m_Value(Low))) ||
         !match(ZextHigh, m_ZExt(m_Value(High))))
-      return nullptr;
+      return std::nullopt;
 
     unsigned HighSize = High->getType()->getScalarSizeInBits();
     unsigned LowSize = Low->getType()->getScalarSizeInBits();
     // Make sure High does not overlap with Low and most significant bits of
     // High aren't shifted out.
     if (ZextHighShlAmt->ult(LowSize) || ZextHighShlAmt->ugt(Width - HighSize))
-      return nullptr;
+      return std::nullopt;
 
     for (User *U : ZextHigh->users()) {
       Value *X, *Y;
@@ -2874,11 +2873,22 @@ static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
   }
 
   if (FShiftArgs.empty())
-    return nullptr;
+    return std::nullopt;
 
   Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
-  Function *F = Intrinsic::getDeclaration(Or.getModule(), IID, Or.getType());
-  return CallInst::Create(F, FShiftArgs);
+  return std::make_tuple(IID, FShiftArgs);
+}
+
+/// Match UB-safe variants of the funnel shift intrinsic.
+static Instruction *matchFunnelShift(Instruction &Or, InstCombinerImpl &IC,
+                                     const DominatorTree &DT) {
+  if (auto Opt = IC.convertShlOrLShrToFShlOrFShr(Or)) {
+    auto [IID, FShiftArgs] = *Opt;
+    Function *F = Intrinsic::getDeclaration(Or.getModule(), IID, Or.getType());
+    return CallInst::Create(F, FShiftArgs);
+  }
+
+  return nullptr;
 }
 
 /// Attempt to combine or(zext(x),shl(zext(y),bw/2) concat packing patterns.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 0bbb22be71569f6..92cdb9cbda113a5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -236,6 +236,9 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
     return getLosslessTrunc(C, TruncTy, Instruction::SExt);
   }
 
+  std::optional<std::tuple<Intrinsic::ID, SmallVector<Value *, 3>>>
+  convertShlOrLShrToFShlOrFShr(Instruction &Or); 
+
 private:
   bool annotateAnyAllocSite(CallBase &Call, const TargetLibraryInfo *TLI);
   bool isDesirableIntType(unsigned BitWidth) const;

[quic-eikansh]

This pull request is created to address the reviews in #66115

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[nikic]

For the purpose you have in mind, I don't think this part should be extracted. Maybe @goldsteinn can confirm.

[quic-eikansh]

I created another pull request #73441 which has all the code needed for my change. I was trying to created stacked pull request. This lead to same changes in different pull request.

For the purpose you have in mind, I don't think this part should be extracted. Maybe @goldsteinn can confirm.

How do you suggest should I do it?

[goldsteinn]

not really sure what @nikic means. Do you mean these ops wont match shl/lshr anyways so its unnecessary? But then what would be alternative?

[quic-eikansh]

Closing as it landed in #73441.