[AggressiveInstCombine] Generalize foldGuardedRotateToFunnelShift to generic funnel shifts

[RKSimon]

Summary

The fold currently only handles rotation patterns, but with the maturation of backend funnel shift handling we can now realistically handle all funnel shift patterns.

This should allow us to begin resolving PR46896 et al.

[RKSimon]

llvm/test/Transforms/AggressiveInstCombine/funnel.ll

430

This does fold to a funnel shift (see rotate.ll) - not sure whether its worth keeping or not.

[spatel]

LGTM

[spatel]

Reopening because the patch was reverted.
Failure example from the reverting commit:

$ cat apedec-reduced.c
a;
b(e) {
  int c;
  unsigned d = f();
  c = d >> 32 - e;
  return c;
}
g() {
  int h = i();
  if (a)
    h = h << a | b(a);
  return h;
}
$ clang -target aarch64-linux-gnu -w -c -O3 apedec-reduced.c
clang: ../lib/Transforms/InstCombine/InstructionCombining.cpp:3656: bool llvm::InstCombinerImpl::run(): Assertion `DT.dominates(BB, UserParent) && "Dominance relation broken?"' failed.

[RKSimon]

Ensure we block poison in a funnel shift value - similar to rG0fe91ad463fea9d08cbcd640a62aa9ca2d8d05e0

[RKSimon]

I still haven't been able to get to the bottom of PR48068

[RKSimon]

Check that the shift values can be hoisted from each basic block.

[mstorsjo]

The original, unreduced testcase seems to work fine now at least - thanks! Can't really comment on the code itself though.

[spatel]

LGTM - the only diff from the earlier rev is that we now check the dominator tree to confirm that the shift ops are safe to hoist.

llvm/lib/Transforms/AggressiveInstCombine/AggressiveInstCombine.cpp

 using namespace llvm;
 using namespace PatternMatch;
 
 #define DEBUG_TYPE "aggressive-instcombine"
 
 STATISTIC(NumAnyOrAllBitsSet, "Number of any/all-bits-set patterns folded");
 STATISTIC(NumGuardedRotates,
           "Number of guarded rotates transformed into funnel shifts");
+STATISTIC(NumGuardedFunnelShifts,
+          "Number of guarded funnel shifts transformed into funnel shifts");
 STATISTIC(NumPopCountRecognized, "Number of popcount idioms recognized");
 
 namespace {
 /// Contains expression pattern combiner logic.
 /// This class provides both the logic to combine expression patterns and
 /// combine them. It differs from InstCombiner class in that each pattern
 /// combiner runs only once as opposed to InstCombine's multi-iteration,
 /// which allows pattern combiner to have higher complexity than the O(1)
public:
   /// Run all expression pattern optimizations on the given /p F function.
   ///
   /// \param F function to optimize.
   /// \returns true if the IR is changed.
   bool runOnFunction(Function &F) override;
 };
 } // namespace
 
-/// Match a pattern for a bitwise rotate operation that partially guards
-/// against undefined behavior by branching around the rotation when the shift
-/// amount is 0.
-static bool foldGuardedRotateToFunnelShift(Instruction &I) {
+/// Match a pattern for a bitwise funnel/rotate operation that partially guards
+/// against undefined behavior by branching around the funnel-shift/rotation
+/// when the shift amount is 0.
+static bool foldGuardedFunnelShift(Instruction &I) {
   if (I.getOpcode() != Instruction::PHI || I.getNumOperands() != 2)
     return false;
 
   // As with the one-use checks below, this is not strictly necessary, but we
   // are being cautious to avoid potential perf regressions on targets that
-  // do not actually have a rotate instruction (where the funnel shift would be
-  // expanded back into math/shift/logic ops).
+  // do not actually have a funnel/rotate instruction (where the funnel shift
+  // would be expanded back into math/shift/logic ops).
   if (!isPowerOf2_32(I.getType()->getScalarSizeInBits()))
     return false;
 
   // Match V to funnel shift left/right and capture the source operands and
   // shift amount.
   auto matchFunnelShift = [](Value *V, Value *&ShVal0, Value *&ShVal1,
                              Value *&ShAmt) {
     Value *SubAmt;
if (match(V,
                               m_LShr(m_Value(ShVal1), m_Value(ShAmt)))))) {
       if (ShAmt == SubAmt) // TODO: Use m_Specific
         return Intrinsic::fshr;
     }
 
     return Intrinsic::not_intrinsic;
   };
 
-  // One phi operand must be a rotate operation, and the other phi operand must
-  // be the source value of that rotate operation:
+  // One phi operand must be a funnel/rotate operation, and the other phi
+  // operand must be the source value of that funnel/rotate operation:
   // phi [ rotate(RotSrc, ShAmt), FunnelBB ], [ RotSrc, GuardBB ]
+  // phi [ fshl(ShlVal0, ShlVal1, ShAmt), FunnelBB ], [ ShlVal0, GuardBB ]
+  // phi [ fshr(ShlVal0, ShlVal1, ShAmt), FunnelBB ], [ ShlVal1, GuardBB ]
   PHINode &Phi = cast<PHINode>(I);
   unsigned FunnelOp = 0, GuardOp = 1;
   Value *P0 = Phi.getOperand(0), *P1 = Phi.getOperand(1);
   Value *ShVal0, *ShVal1, *ShAmt;
   Intrinsic::ID IID = matchFunnelShift(P0, ShVal0, ShVal1, ShAmt);
-  if (IID == Intrinsic::not_intrinsic || ShVal0 != ShVal1 || ShVal0 != P1) {
+  if (IID == Intrinsic::not_intrinsic ||
+      (IID == Intrinsic::fshl && ShVal0 != P1) ||
+      (IID == Intrinsic::fshr && ShVal1 != P1)) {
     IID = matchFunnelShift(P1, ShVal0, ShVal1, ShAmt);
-    if (IID == Intrinsic::not_intrinsic || ShVal0 != ShVal1 || ShVal0 != P0)
+    if (IID == Intrinsic::not_intrinsic ||
+        (IID == Intrinsic::fshl && ShVal0 != P0) ||
+        (IID == Intrinsic::fshr && ShVal1 != P0))
       return false;
     assert((IID == Intrinsic::fshl || IID == Intrinsic::fshr) &&
            "Pattern must match funnel shift left or right");
     std::swap(FunnelOp, GuardOp);
   }
-  assert(ShVal0 == ShVal1 && "Rotation funnel shift pattern expected");
 
   // The incoming block with our source operand must be the "guard" block.
-  // That must contain a cmp+branch to avoid the rotate when the shift amount
-  // is equal to 0. The other incoming block is the block with the rotate.
+  // That must contain a cmp+branch to avoid the funnel/rotate when the shift
+  // amount is equal to 0. The other incoming block is the block with the
+  // funnel/rotate.
   BasicBlock *GuardBB = Phi.getIncomingBlock(GuardOp);
   BasicBlock *FunnelBB = Phi.getIncomingBlock(FunnelOp);
   Instruction *TermI = GuardBB->getTerminator();
   ICmpInst::Predicate Pred;
   BasicBlock *PhiBB = Phi.getParent();
   if (!match(TermI, m_Br(m_ICmp(Pred, m_Specific(ShAmt), m_ZeroInt()),
                          m_SpecificBB(PhiBB), m_SpecificBB(FunnelBB))))
     return false;
 
   if (Pred != CmpInst::ICMP_EQ)
     return false;
 
   // We matched a variation of this IR pattern:
   // GuardBB:
   //   %cmp = icmp eq i32 %ShAmt, 0
   //   br i1 %cmp, label %PhiBB, label %FunnelBB
   // FunnelBB:
   //   %sub = sub i32 32, %ShAmt
-  //   %shr = lshr i32 %RotSrc, %sub
-  //   %shl = shl i32 %RotSrc, %ShAmt
-  //   %rot = or i32 %shr, %shl
+  //   %shr = lshr i32 %ShVal1, %sub
+  //   %shl = shl i32 %ShVal0, %ShAmt
+  //   %fsh = or i32 %shr, %shl
   //   br label %PhiBB
   // PhiBB:
-  //   %cond = phi i32 [ %RotSrc, %FunnelBB ], [ %RotSrc, %GuardBB ]
+  //   %cond = phi i32 [ %fsh, %FunnelBB ], [ %ShVal0, %GuardBB ]
   // -->
-  // llvm.fshl.i32(i32 %RotSrc, i32 %RotSrc, i32 %ShAmt)
+  // llvm.fshl.i32(i32 %ShVal0, i32 %ShVal1, i32 %ShAmt)
   IRBuilder<> Builder(PhiBB, PhiBB->getFirstInsertionPt());
   Function *F = Intrinsic::getDeclaration(Phi.getModule(), IID, Phi.getType());
   Phi.replaceAllUsesWith(Builder.CreateCall(F, {ShVal0, ShVal1, ShAmt}));
+  if (ShVal0 == ShVal1)
     ++NumGuardedRotates;
+  else
+    ++NumGuardedFunnelShifts;
   return true;
 }
 
 /// This is used by foldAnyOrAllBitsSet() to capture a source value (Root) and
 /// the bit indexes (Mask) needed by a masked compare. If we're matching a chain
 /// of 'and' ops, then we also need to capture the fact that we saw an
 /// "and X, 1", so that's an extra return value for that case.
 struct MaskOps {
for (BasicBlock &BB : F) {
     // Do not delete instructions under here and invalidate the iterator.
     // Walk the block backwards for efficiency. We're matching a chain of
     // use->defs, so we're more likely to succeed by starting from the bottom.
     // Also, we want to avoid matching partial patterns.
     // TODO: It would be more efficient if we removed dead instructions
     // iteratively in this loop rather than waiting until the end.
     for (Instruction &I : make_range(BB.rbegin(), BB.rend())) {
       MadeChange |= foldAnyOrAllBitsSet(I);
-      MadeChange |= foldGuardedRotateToFunnelShift(I);
+      MadeChange |= foldGuardedFunnelShift(I);
       MadeChange |= tryToRecognizePopCount(I); 
     }
   }
 
   // We're done with transforms, so remove dead instructions.
   if (MadeChange)
     for (BasicBlock &BB : F)
       SimplifyInstructionsInBlock(&BB);

llvm/test/Transforms/AggressiveInstCombine/funnel.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -aggressive-instcombine -S | FileCheck %s
 
 define i32 @fshl(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @fshl(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[SUB]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[A:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHR]], [[SHL]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[OR]], [[FSHBB]] ], [ [[A]], [[ENTRY:%.*]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshl.i32(i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c
   %shr = lshr i32 %b, %sub
   %shl = shl i32 %a, %c
   %or = or i32 %shr, %shl
   br label %end
 
 end:
   %cond = phi i32 [ %or, %fshbb ], [ %a, %entry ]
   ret i32 %cond
 }
 
 define i32 @fshl_commute_phi(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @fshl_commute_phi(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[SUB]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[A:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHR]], [[SHL]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[A]], [[ENTRY:%.*]] ], [ [[OR]], [[FSHBB]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshl.i32(i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c
   %shr = lshr i32 %b, %sub
   %shl = shl i32 %a, %c
   %or = or i32 %shr, %shl
   br label %end
 
 end:
   %cond = phi i32 [ %a, %entry ], [ %or, %fshbb ]
   ret i32 %cond
 }
 
 define i32 @fshl_commute_or(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @fshl_commute_or(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[SUB]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[A:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHL]], [[SHR]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[A]], [[ENTRY:%.*]] ], [ [[OR]], [[FSHBB]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshl.i32(i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c
   %shr = lshr i32 %b, %sub

 ; Verify that the intrinsic is inserted into a valid position.
 
 define i32 @fshl_insert_valid_location(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @fshl_insert_valid_location(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[SUB]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[A:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHR]], [[SHL]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[OR]], [[FSHBB]] ], [ [[A]], [[ENTRY:%.*]] ]
-; CHECK-NEXT:    [[OTHER:%.*]] = phi i32 [ 1, [[FSHBB]] ], [ 2, [[ENTRY]] ]
-; CHECK-NEXT:    [[RES:%.*]] = or i32 [[COND]], [[OTHER]]
+; CHECK-NEXT:    [[OTHER:%.*]] = phi i32 [ 1, [[FSHBB]] ], [ 2, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshl.i32(i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    [[RES:%.*]] = or i32 [[TMP0]], [[OTHER]]
 ; CHECK-NEXT:    ret i32 [[RES]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c

 }
 
 define i32 @fshr(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @fshr(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[A:%.*]], [[SUB]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHR]], [[SHL]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[OR]], [[FSHBB]] ], [ [[B]], [[ENTRY:%.*]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshr.i32(i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c
   %shl = shl i32 %a, %sub
   %shr = lshr i32 %b, %c
   %or = or i32 %shr, %shl
   br label %end
 
 end:
   %cond = phi i32 [ %or, %fshbb ], [ %b, %entry ]
   ret i32 %cond
 }
 
 define i32 @fshr_commute_phi(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @fshr_commute_phi(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[A:%.*]], [[SUB]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHR]], [[SHL]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[B]], [[ENTRY:%.*]] ], [ [[OR]], [[FSHBB]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshr.i32(i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c
   %shl = shl i32 %a, %sub
   %shr = lshr i32 %b, %c
   %or = or i32 %shr, %shl
   br label %end
 
 end:
   %cond = phi i32 [ %b, %entry ], [ %or, %fshbb ]
   ret i32 %cond
 }
 
 define i32 @fshr_commute_or(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @fshr_commute_or(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[A:%.*]], [[SUB]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHL]], [[SHR]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[B]], [[ENTRY:%.*]] ], [ [[OR]], [[FSHBB]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshr.i32(i32 [[A:%.*]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c
   %shl = shl i32 %a, %sub
fshbb:
   %or = or i32 %shl, %shr
   br label %end
 
 end:
   %cond = phi i32 [ %b, %entry ], [ %or, %fshbb ]
   ret i32 %cond
 }
 
-; Negative test - wrong shift.
+; Negative test - wrong shift for rotate (but can be folded to a generic funnel shift).
 
 define i32 @not_fshr_5(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @not_fshr_5(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]
 ; CHECK:       fshbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[C]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[C]], [[SUB]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[B:%.*]], [[C]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHL]], [[SHR]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[B]], [[ENTRY:%.*]] ], [ [[OR]], [[FSHBB]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshr.i32(i32 [[C]], i32 [[B:%.*]], i32 [[C]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %c, 0
   br i1 %cmp, label %end, label %fshbb
 
 fshbb:
   %sub = sub i32 32, %c
   %shl = shl i32 %c, %sub
   %shr = lshr i32 %b, %c
   %or = or i32 %shl, %shr
   br label %end
 
 end:
   %cond = phi i32 [ %b, %entry ], [ %or, %fshbb ]
   ret i32 %cond
 }
 
 ; Negative test - wrong sub.
 
 define i32 @not_fshr_6(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: @not_fshr_6(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[FSHBB:%.*]]

llvm/test/Transforms/AggressiveInstCombine/rotate.ll

rotbb:
   %or = or i32 %shl, %shr
   br label %end
 
 end:
   %cond = phi i32 [ %a, %entry ], [ %or, %rotbb ]
   ret i32 %cond
 }
 
-; Negative test - wrong shift.
+; Negative test - wrong shift for rotate (but can be folded to a generic funnel shift).
 
 define i32 @not_rotr_5(i32 %a, i32 %b) {
 ; CHECK-LABEL: @not_rotr_5(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[B:%.*]], 0
 ; CHECK-NEXT:    br i1 [[CMP]], label [[END:%.*]], label [[ROTBB:%.*]]
 ; CHECK:       rotbb:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 32, [[B]]
-; CHECK-NEXT:    [[SHL:%.*]] = shl i32 [[B]], [[SUB]]
-; CHECK-NEXT:    [[SHR:%.*]] = lshr i32 [[A:%.*]], [[B]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[SHL]], [[SHR]]
 ; CHECK-NEXT:    br label [[END]]
 ; CHECK:       end:
-; CHECK-NEXT:    [[COND:%.*]] = phi i32 [ [[A]], [[ENTRY:%.*]] ], [ [[OR]], [[ROTBB]] ]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.fshr.i32(i32 [[B]], i32 [[A:%.*]], i32 [[B]])
+; CHECK-NEXT:    ret i32 [[TMP0]]
 ;
 entry:
   %cmp = icmp eq i32 %b, 0
   br i1 %cmp, label %end, label %rotbb
 
 rotbb:
   %sub = sub i32 32, %b
   %shl = shl i32 %b, %sub