Revert [InstCombine] Shift amount reassociation: shl-trunc-shl pattern

This reverts r368059 (git commit 0f957109761913c563922f1afd4ceb29ef21bbd0)

This caused Clang to assert while self-hosting and compiling
SystemZInstrInfo.cpp. Reduction is running.

llvm-svn: 368084

1 files changed, 24 insertions, 66 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index b822761422c..c0a1df6b9a7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -27,84 +27,42 @@ using namespace PatternMatch;
 // This is valid for any shift, but they must be identical.
 static Instruction *
 reassociateShiftAmtsOfTwoSameDirectionShifts(BinaryOperator *Sh0,
-                                             const SimplifyQuery &SQ,
-                                             InstCombiner::BuilderTy &Builder) {
-  // Look for a shift of some instruction, ignore zext of shift amount if any.
-  Instruction *Sh0Op0;
-  Value *ShAmt0;
-  if (!match(Sh0,
-             m_Shift(m_Instruction(Sh0Op0), m_ZExtOrSelf(m_Value(ShAmt0)))))
-    return nullptr;
-
-  // If there is a truncation between the two shifts, we must make note of it
-  // and look through it. The truncation imposes additional constraints on the
-  // transform.
+                                             const SimplifyQuery &SQ) {
+  // Look for:  (x shiftopcode ShAmt0) shiftopcode ShAmt1
+  Value *X, *ShAmt1, *ShAmt0;
   Instruction *Sh1;
-  Value *Trunc = nullptr;
-  match(Sh0Op0,
-        m_CombineOr(m_CombineAnd(m_Trunc(m_Instruction(Sh1)), m_Value(Trunc)),
-                    m_Instruction(Sh1)));
-
-  // Inner shift: (x shiftopcode ShAmt1)
-  Value *X, *ShAmt1;
-  if (!match(Sh1, m_Shift(m_Value(X), m_ZExtOrSelf(m_Value(ShAmt1)))))
+  if (!match(Sh0, m_Shift(m_CombineAnd(m_Shift(m_Value(X), m_Value(ShAmt1)),
+                                       m_Instruction(Sh1)),
+                          m_Value(ShAmt0))))
     return nullptr;
 
   // The shift opcodes must be identical.
   Instruction::BinaryOps ShiftOpcode = Sh0->getOpcode();
   if (ShiftOpcode != Sh1->getOpcode())
     return nullptr;
-
-  // Did we match a pattern with truncation ?
-  if (Trunc) {
-    // For right-shifts we can't do any such simplifications. Leave as-is.
-    if (ShiftOpcode != Instruction::BinaryOps::Shl)
-      return nullptr; // FIXME: still could perform constant-folding.
-    // If we saw truncation, we'll need to produce extra instruction,
-    // and for that one of the operands of the shift must be one-use.
-    if (!match(Sh0, m_c_BinOp(m_OneUse(m_Value()), m_Value())))
-      return nullptr;
-  }
-
   // Can we fold (ShAmt0+ShAmt1) ?
-  auto *NewShAmt = dyn_cast_or_null<Constant>(
-      SimplifyAddInst(ShAmt0, ShAmt1, /*isNSW=*/false, /*isNUW=*/false,
-                      SQ.getWithInstruction(Sh0)));
+  Value *NewShAmt = SimplifyBinOp(Instruction::BinaryOps::Add, ShAmt0, ShAmt1,
+                                  SQ.getWithInstruction(Sh0));
   if (!NewShAmt)
     return nullptr; // Did not simplify.
-  // Is the new shift amount smaller than the bit width of inner shift?
-  if (!match(NewShAmt, m_SpecificInt_ICMP(
-                           ICmpInst::Predicate::ICMP_ULT,
-                           APInt(NewShAmt->getType()->getScalarSizeInBits(),
-                                 X->getType()->getScalarSizeInBits()))))
-    return nullptr; // FIXME: could perform constant-folding.
-
+  // Is the new shift amount smaller than the bit width?
+  // FIXME: could also rely on ConstantRange.
+  unsigned BitWidth = X->getType()->getScalarSizeInBits();
+  if (!match(NewShAmt, m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_ULT,
+                                          APInt(BitWidth, BitWidth))))
+    return nullptr;
   // All good, we can do this fold.
-  NewShAmt = ConstantExpr::getZExtOrBitCast(NewShAmt, X->getType());
-
   BinaryOperator *NewShift = BinaryOperator::Create(ShiftOpcode, X, NewShAmt);
-
-  // The flags can only be propagated if there wasn't a trunc.
-  if (!Trunc) {
-    // If the pattern did not involve trunc, and both of the original shifts
-    // had the same flag set, preserve the flag.
-    if (ShiftOpcode == Instruction::BinaryOps::Shl) {
-      NewShift->setHasNoUnsignedWrap(Sh0->hasNoUnsignedWrap() &&
-                                     Sh1->hasNoUnsignedWrap());
-      NewShift->setHasNoSignedWrap(Sh0->hasNoSignedWrap() &&
-                                   Sh1->hasNoSignedWrap());
-    } else {
-      NewShift->setIsExact(Sh0->isExact() && Sh1->isExact());
-    }
+  // If both of the original shifts had the same flag set, preserve the flag.
+  if (ShiftOpcode == Instruction::BinaryOps::Shl) {
+    NewShift->setHasNoUnsignedWrap(Sh0->hasNoUnsignedWrap() &&
+                                   Sh1->hasNoUnsignedWrap());
+    NewShift->setHasNoSignedWrap(Sh0->hasNoSignedWrap() &&
+                                 Sh1->hasNoSignedWrap());
+  } else {
+    NewShift->setIsExact(Sh0->isExact() && Sh1->isExact());
   }
-
-  Instruction *Ret = NewShift;
-  if (Trunc) {
-    Builder.Insert(NewShift);
-    Ret = CastInst::Create(Instruction::Trunc, NewShift, Sh0->getType());
-  }
-
-  return Ret;
+  return NewShift;
 }
 
 // If we have some pattern that leaves only some low bits set, and then performs
@@ -200,7 +158,7 @@ Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
       return Res;
 
   if (Instruction *NewShift =
-          reassociateShiftAmtsOfTwoSameDirectionShifts(&I, SQ, Builder))
+          reassociateShiftAmtsOfTwoSameDirectionShifts(&I, SQ))
     return NewShift;
 
   // (C1 shift (A add C2)) -> (C1 shift C2) shift A)