[InstCombine] Shift amount reassociation in bittest: trunc-of-lshr (PR42399)

[lebedev.ri]

Summary

Finally, the fold i was looking forward to :)

The legality check is muddy, i doubt i've groked the full generalization,
but it handles all the cases i care about, and can come up with:
https://rise4fun.com/Alive/26j

I.e. we can perform the fold if any of the following is true:

• The shift amount is either zero or one less than widest bitwidth
• Either of the values being shifted has at most lowest bit set
• The value that is being shifted by shl (which is not truncated) should have no less leading zeros than the total shift amount;
• The value that is being shifted by lshr (which is truncated) should have no less leading zeros than the widest bit width minus total shift amount minus one

I strongly suspect there is some better generalization, but i'm not aware of it as of right now.
For now i also avoided using actual computeKnownBits(), but restricted it to constants.

[lebedev.ri]

Cleanup diff by precommitting NFC cleanup,

[lebedev.ri]

bump

[lebedev.ri]

@spatel ping

[xbolva00]

Does this show up in bootstrap/test suite?

Rare folds with big pattern matching should go to AgressiveInstCombine.

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

3383

Use ´WidestBitWidth´

3396

Hoist it

3432

Replace 63 with WidestBitWidth - 1?

[lebedev.ri]

In D66383#1648970, @xbolva00 wrote:

Does this show up in bootstrap/test suite?

I have not checked this particular pattern extensions,
but i know it does appear in hotspots in my code which is why i'm trying to add these folds :S

Rare folds with big pattern matching should go to AgressiveInstCombine.

Yes it is a concern indeed, but we've had this disscussion in https://reviews.llvm.org/D64512#1587640 already, this isn't much different.

[spatel]

A few clean-ups noted inline.

If I'm reading it correctly, this is more complicated than it could be only to support arbitrary vector constants. Do we have any evidence that says we need that support?

We've come this far on this series of patches without raising that question, so I'm not going to object to this particular patch now. But I think we should keep the code simpler unless we know there's a reason to handle the arbitrary vector constant pattern. It seems too rare to me to warrant this much effort.

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

3389

I don't see the value of the 'Check' lambda. Just do this check inline?

3390

"Cst" is ambiguous (I always read that as "Cast"). "MatchCmpInteger"?

3396

Move this local variable declaration/assignment up, so it can be used in lines 3383/3384?

3422

typo: 'the the'

3425

We prefer "auto *" based on current guidelines:
http://llvm.org/docs/CodingStandards.html#use-auto-type-deduction-to-make-code-more-readable

3431

We prefer "auto *" based on current guidelines.

3432

Generalize "63" to "WideWidth - 1"?

[lebedev.ri]

In D66383#1649115, @spatel wrote:

A few clean-ups noted inline.

If I'm reading it correctly, this is more complicated than it could be only to support arbitrary vector constants. Do we have any evidence that says we need that support?

We've come this far on this series of patches without raising that question, so I'm not going to object to this particular patch now. But I think we should keep the code simpler unless we know there's a reason to handle the arbitrary vector constant pattern. It seems too rare to me to warrant this much effort.

Indeed, non-splat support is ugly here, and incomplete still.
I don't have any evidence, and furthermore i only need scalar support from this, so i will happily cripple it.

[lebedev.ri]

Rebased, addressed review notes, pessimized vectors even more.

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

3389

It will result in ugly cascade of if's - if one of preconditions does not match we can't just abort,
some next precondition can still match and thus allow the fold.
I believe it is better to keep lambda here.

3425

Whoops, this was not intentional.

[spatel]

LGTM - still complicated, but easier to read without the ConstExpr logic. :)

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

3394–3396

That's a confusing name for the common (scalar) case since that's not a splat. "NewShAmtC" ?

[lebedev.ri]

In D66383#1649684, @spatel wrote:

LGTM

Thank you for the review!

still complicated, but easier to read without the ConstExpr logic. :)

Yeah :/ I'm likely missing some generalization.

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

foldICmpWithTruncSignExtendedVal(ICmpInst &I,
   return T1;
 }
 
 // Given pattern:
 //   icmp eq/ne (and ((x shift Q), (y oppositeshift K))), 0
 // we should move shifts to the same hand of 'and', i.e. rewrite as
 //   icmp eq/ne (and (x shift (Q+K)), y), 0  iff (Q+K) u< bitwidth(x)
 // We are only interested in opposite logical shifts here.
-// One of the shifts can be truncated. For now, it can only be 'shl'.
+// One of the shifts can be truncated.
 // If we can, we want to end up creating 'lshr' shift.
 static Value *
 foldShiftIntoShiftInAnotherHandOfAndInICmp(ICmpInst &I, const SimplifyQuery SQ,
                                            InstCombiner::BuilderTy &Builder) {
   if (!I.isEquality() || !match(I.getOperand(1), m_Zero()) ||
       !I.getOperand(0)->hasOneUse())
     return nullptr;
 
foldShiftIntoShiftInAnotherHandOfAndInICmp(ICmpInst &I, const SimplifyQuery SQ,
   // Or they both have identical types if there was no truncation.
   Instruction *NarrowestShift = XShift;
 
   Type *WidestTy = WidestShift->getType();
   assert(NarrowestShift->getType() == I.getOperand(0)->getType() &&
          "We did not look past any shifts while matching XShift though.");
   bool HadTrunc = WidestTy != I.getOperand(0)->getType();
 
-  if (HadTrunc) {
-    // We did indeed have a truncation. For now, let's only proceed if the 'shl'
-    // was truncated, since that does not require any extra legality checks.
-    // FIXME: trunc-of-lshr.
-    if (!match(YShift, m_Shl(m_Value(), m_Value())))
-      return nullptr;
-  }
-
   // If YShift is a 'lshr', swap the shifts around.
   if (match(YShift, m_LShr(m_Value(), m_Value())))
     std::swap(XShift, YShift);
 
   // The shifts must be in opposite directions.
   auto XShiftOpcode = XShift->getOpcode();
   if (XShiftOpcode == YShift->getOpcode())
     return nullptr; // Do not care about same-direction shifts here.
if (XShAmt->getType() != YShAmt->getType())
     return nullptr;
 
   // Can we fold (XShAmt+YShAmt) ?
   auto *NewShAmt = dyn_cast_or_null<Constant>(
       SimplifyAddInst(XShAmt, YShAmt, /*isNSW=*/false,
                       /*isNUW=*/false, SQ.getWithInstruction(&I)));
   if (!NewShAmt)
     return nullptr;
+  NewShAmt = ConstantExpr::getZExtOrBitCast(NewShAmt, WidestTy);
+
   // Is the new shift amount smaller than the bit width?
   // FIXME: could also rely on ConstantRange.
-  if (!match(NewShAmt, m_SpecificInt_ICMP(
-                           ICmpInst::Predicate::ICMP_ULT,
-                           APInt(NewShAmt->getType()->getScalarSizeInBits(),
+  if (!match(NewShAmt,
+             m_SpecificInt_ICMP(ICmpInst::Predicate::ICMP_ULT,
+                                APInt(WidestTy->getScalarSizeInBits(),
                                       WidestTy->getScalarSizeInBits()))))
     return nullptr;
+
+  // An extra legality check is needed if we had trunc-of-lshr.
+  if (HadTrunc && match(WidestShift, m_LShr(m_Value(), m_Value()))) {
+    auto Check = [SQ, WidestShift, NarrowestShift, NewShAmt, WidestTy]() {
+      auto CstMatch = [](Value *V, ICmpInst::Predicate Predicate,
+                         uint64_t Val) {
+        return match(
+            V, m_SpecificInt_ICMP(
+                   Predicate, APInt(V->getType()->getScalarSizeInBits(), Val)));
+      };
+      unsigned WidestBitWidth = WidestTy->getScalarSizeInBits();
+
+      // It isn't obvious whether it's worth it to analyze non-constants here.
+      // If *any* of these preconditions matches we can perform the fold.
+
+      // If either of the values being shifted has at most lowest bit set
+      // we always can perform the fold.
+      auto UleOne = [CstMatch](Value *V) {
+        return CstMatch(V, ICmpInst::Predicate::ICMP_ULE, 1);
+      };
+      if (UleOne(NarrowestShift->getOperand(0)) ||
+          UleOne(WidestShift->getOperand(0)))
+        return true;
+
+      // If it's edge-case shift - either by 0 or by bitwidth-1 we can fold.
+      if (match(
+              ConstantExpr::getOr(
+                  ConstantExpr::getICmp(ICmpInst::Predicate::ICMP_EQ, NewShAmt,
+                                        Constant::getNullValue(WidestTy)),
+                  ConstantExpr::getICmp(
+                      ICmpInst::Predicate::ICMP_EQ, NewShAmt,
+                      ConstantInt::get(WidestTy, WidestBitWidth - 1))),
+              m_One()))
+        return true;
+
+      // We consider *min* leading zeros so a single outlier
+      // blocks the the transform as opposed to allowing it.
+      // FIXME: this is pessimistic for vectors.
+
+      if (auto C = dyn_cast<Constant>(NarrowestShift->getOperand(0))) {
+        // Precondition:  NewShAmt u<= countLeadingZeros(C)
+        if (CstMatch(NewShAmt, ICmpInst::Predicate::ICMP_ULE,
+                     computeKnownBits(C, SQ.DL).countMinLeadingZeros()))
+          return true;
+      }
+      if (auto C = dyn_cast<Constant>(WidestShift->getOperand(0))) {
+        // Precondition:  (63-NewShAmt) u<= countLeadingZeros(C)
+        KnownBits K = computeKnownBits(C, SQ.DL);
+        auto AdjNewShAmt = ConstantExpr::getSub(
+            ConstantInt::get(C->getType(), WidestBitWidth - 1), NewShAmt);
+        if (CstMatch(AdjNewShAmt, ICmpInst::Predicate::ICMP_ULE,
+                     computeKnownBits(C, SQ.DL).countMinLeadingZeros()))
+          return true;
+      }
+      return false;
+    };
+    if (!Check())
+      return nullptr;
+  }
+
   // All good, we can do this fold.
-  NewShAmt = ConstantExpr::getZExtOrBitCast(NewShAmt, WidestTy);
   X = Builder.CreateZExt(X, WidestTy);
+  Y = Builder.CreateZExt(Y, WidestTy);
   // The shift is the same that was for X.
   Value *T0 = XShiftOpcode == Instruction::BinaryOps::LShr
                   ? Builder.CreateLShr(X, NewShAmt)
                   : Builder.CreateShl(X, NewShAmt);
   Value *T1 = Builder.CreateAnd(T0, Y);
   return Builder.CreateICmp(I.getPredicate(), T1,
                             Constant::getNullValue(WidestTy));
 }

llvm/test/Transforms/InstCombine/shift-amount-reassociation-in-bittest-with-truncation-lshr.ll

;
   ret i1 %t5
 }
 
 ; However we can fold if %x/%y are constants that pass extra legality check.
 
 ; New shift amount would be 16, %x has 16 leading zeros - can fold.
 define i1 @t1(i64 %y, i32 %len) {
 ; CHECK-LABEL: @t1(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 32, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 65535, [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -16
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[Y:%.*]], 4294901760
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i64 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %t0 = sub i32 32, %len
   %t1 = shl i32 65535, %t0
   %t2 = add i32 %len, -16
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 %y, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc
   %t5 = icmp ne i32 %t4, 0
   ret i1 %t5
 }
 ; Note that we indeed look at leading zeros!
 define i1 @t1_single_bit(i64 %y, i32 %len) {
 ; CHECK-LABEL: @t1_single_bit(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 32, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 32768, [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -16
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[Y:%.*]], 2147483648
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i64 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %t0 = sub i32 32, %len
   %t1 = shl i32 32768, %t0
   %t2 = add i32 %len, -16
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 %y, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc
;
   %t4 = and i32 %t1, %t3_trunc
   %t5 = icmp ne i32 %t4, 0
   ret i1 %t5
 }
 
 ; New shift amount would be 16, %y has 47 leading zeros - can fold.
 define i1 @t3(i32 %x, i32 %len) {
 ; CHECK-LABEL: @t3(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 32, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -16
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 131071, [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[X:%.*]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i32 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %t0 = sub i32 32, %len
   %t1 = shl i32 %x, %t0
   %t2 = add i32 %len, -16
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 131071, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc
   %t5 = icmp ne i32 %t4, 0
   ret i1 %t5
 }
 ; Note that we indeed look at leading zeros!
 define i1 @t3_singlebit(i32 %x, i32 %len) {
 ; CHECK-LABEL: @t3_singlebit(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 32, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -16
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 65536, [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[X:%.*]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i32 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %t0 = sub i32 32, %len
   %t1 = shl i32 %x, %t0
   %t2 = add i32 %len, -16
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 65536, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc

 
 ;-------------------------------------------------------------------------------
 ; Vector tests
 ;-------------------------------------------------------------------------------
 
 ; New shift amount would be 16, minimal count of leading zeros in %x is 16. Ok.
 define <2 x i1> @t5_vec(<2 x i64> %y, <2 x i32> %len) {
 ; CHECK-LABEL: @t5_vec(
-; CHECK-NEXT:    [[T0:%.*]] = sub <2 x i32> <i32 32, i32 32>, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl <2 x i32> <i32 65535, i32 32767>, [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add <2 x i32> [[LEN]], <i32 -16, i32 -16>
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext <2 x i32> [[T2]] to <2 x i64>
-; CHECK-NEXT:    [[T3:%.*]] = lshr <2 x i64> [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc <2 x i64> [[T3]] to <2 x i32>
-; CHECK-NEXT:    [[T4:%.*]] = and <2 x i32> [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne <2 x i32> [[T4]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr <2 x i64> [[Y:%.*]], <i64 16, i64 16>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i64> [[TMP1]], <i64 65535, i64 32767>
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne <2 x i64> [[TMP2]], zeroinitializer
+; CHECK-NEXT:    ret <2 x i1> [[TMP3]]
 ;
   %t0 = sub <2 x i32> <i32 32, i32 32>, %len
   %t1 = shl <2 x i32> <i32 65535, i32 32767>, %t0
   %t2 = add <2 x i32> %len, <i32 -16, i32 -16>
   %t2_wide = zext <2 x i32> %t2 to <2 x i64>
   %t3 = lshr <2 x i64> %y, %t2_wide
   %t3_trunc = trunc <2 x i64> %t3 to <2 x i32>
   %t4 = and <2 x i32> %t1, %t3_trunc
;
   %t4 = and <2 x i32> %t1, %t3_trunc
   %t5 = icmp ne <2 x i32> %t4, <i32 0, i32 0>
   ret <2 x i1> %t5
 }
 
 ; New shift amount would be 16, minimal count of leading zeros in %x is 47. Ok.
 define <2 x i1> @t7_vec(<2 x i32> %x, <2 x i32> %len) {
 ; CHECK-LABEL: @t7_vec(
-; CHECK-NEXT:    [[T0:%.*]] = sub <2 x i32> <i32 32, i32 32>, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl <2 x i32> [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add <2 x i32> [[LEN]], <i32 -16, i32 -16>
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext <2 x i32> [[T2]] to <2 x i64>
-; CHECK-NEXT:    [[T3:%.*]] = lshr <2 x i64> <i64 131071, i64 65535>, [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc <2 x i64> [[T3]] to <2 x i32>
-; CHECK-NEXT:    [[T4:%.*]] = and <2 x i32> [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne <2 x i32> [[T4]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and <2 x i32> [[X:%.*]], <i32 1, i32 0>
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne <2 x i32> [[TMP1]], zeroinitializer
+; CHECK-NEXT:    ret <2 x i1> [[TMP2]]
 ;
   %t0 = sub <2 x i32> <i32 32, i32 32>, %len
   %t1 = shl <2 x i32> %x, %t0
   %t2 = add <2 x i32> %len, <i32 -16, i32 -16>
   %t2_wide = zext <2 x i32> %t2 to <2 x i64>
   %t3 = lshr <2 x i64> <i64 131071, i64 65535>, %t2_wide
   %t3_trunc = trunc <2 x i64> %t3 to <2 x i32>
   %t4 = and <2 x i32> %t1, %t3_trunc
;
   ret <2 x i1> %t5
 }
 
 ;-------------------------------------------------------------------------------
 
 ; Ok if the final shift amount is exactly one less than widest bit width.
 define i1 @t9_highest_bit(i32 %x, i64 %y, i32 %len) {
 ; CHECK-LABEL: @t9_highest_bit(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 64, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -1
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i32 [[X:%.*]] to i64
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr i64 [[Y:%.*]], 63
+; CHECK-NEXT:    [[TMP3:%.*]] = and i64 [[TMP2]], [[TMP1]]
+; CHECK-NEXT:    [[TMP4:%.*]] = icmp ne i64 [[TMP3]], 0
+; CHECK-NEXT:    ret i1 [[TMP4]]
 ;
   %t0 = sub i32 64, %len
   %t1 = shl i32 %x, %t0
   %t2 = add i32 %len, -1
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 %y, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc
;
   %t4 = and i32 %t1, %t3_trunc
   %t5 = icmp ne i32 %t4, 0
   ret i1 %t5
 }
 
 ; Ok if the final shift amount is zero.
 define i1 @t11_no_shift(i32 %x, i64 %y, i32 %len) {
 ; CHECK-LABEL: @t11_no_shift(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 64, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -64
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i32 [[X:%.*]] to i64
+; CHECK-NEXT:    [[TMP2:%.*]] = and i64 [[TMP1]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i64 [[TMP2]], 0
+; CHECK-NEXT:    ret i1 [[TMP3]]
 ;
   %t0 = sub i32 64, %len
   %t1 = shl i32 %x, %t0
   %t2 = add i32 %len, -64
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 %y, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc
;
   %t4 = and i32 %t1, %t3_trunc
   %t5 = icmp ne i32 %t4, 0
   ret i1 %t5
 }
 
 ; A mix of those conditions is ok.
 define <2 x i1> @t11_zero_and_almost_bitwidth(<2 x i32> %x, <2 x i64> %y, <2 x i32> %len) {
 ; CHECK-LABEL: @t11_zero_and_almost_bitwidth(
-; CHECK-NEXT:    [[T0:%.*]] = sub <2 x i32> <i32 64, i32 64>, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl <2 x i32> [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add <2 x i32> [[LEN]], <i32 -1, i32 -64>
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext <2 x i32> [[T2]] to <2 x i64>
-; CHECK-NEXT:    [[T3:%.*]] = lshr <2 x i64> [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc <2 x i64> [[T3]] to <2 x i32>
-; CHECK-NEXT:    [[T4:%.*]] = and <2 x i32> [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne <2 x i32> [[T4]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = zext <2 x i32> [[X:%.*]] to <2 x i64>
+; CHECK-NEXT:    [[TMP2:%.*]] = lshr <2 x i64> [[Y:%.*]], <i64 63, i64 0>
+; CHECK-NEXT:    [[TMP3:%.*]] = and <2 x i64> [[TMP2]], [[TMP1]]
+; CHECK-NEXT:    [[TMP4:%.*]] = icmp ne <2 x i64> [[TMP3]], zeroinitializer
+; CHECK-NEXT:    ret <2 x i1> [[TMP4]]
 ;
   %t0 = sub <2 x i32> <i32 64, i32 64>, %len
   %t1 = shl <2 x i32> %x, %t0
   %t2 = add <2 x i32> %len, <i32 -1, i32 -64>
   %t2_wide = zext <2 x i32> %t2 to <2 x i64>
   %t3 = lshr <2 x i64> %y, %t2_wide
   %t3_trunc = trunc <2 x i64> %t3 to <2 x i32>
   %t4 = and <2 x i32> %t1, %t3_trunc
;
   ret <2 x i1> %t5
 }
 
 ;------------------------------------------------------------------------------;
 
 ; Ok if one of the values being shifted is 1
 define i1 @t13_x_is_one(i64 %y, i32 %len) {
 ; CHECK-LABEL: @t13_x_is_one(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 32, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 1, [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -16
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[Y:%.*]], 65536
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i64 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %t0 = sub i32 32, %len
   %t1 = shl i32 1, %t0
   %t2 = add i32 %len, -16
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 %y, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc
   %t5 = icmp ne i32 %t4, 0
   ret i1 %t5
 }
 define i1 @t14_x_is_one(i32 %x, i32 %len) {
 ; CHECK-LABEL: @t14_x_is_one(
-; CHECK-NEXT:    [[T0:%.*]] = sub i32 32, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl i32 [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add i32 [[LEN]], -16
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext i32 [[T2]] to i64
-; CHECK-NEXT:    [[T3:%.*]] = lshr i64 1, [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc i64 [[T3]] to i32
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    ret i1 false
 ;
   %t0 = sub i32 32, %len
   %t1 = shl i32 %x, %t0
   %t2 = add i32 %len, -16
   %t2_wide = zext i32 %t2 to i64
   %t3 = lshr i64 1, %t2_wide
   %t3_trunc = trunc i64 %t3 to i32
   %t4 = and i32 %t1, %t3_trunc
   %t5 = icmp ne i32 %t4, 0
   ret i1 %t5
 }
 
 define <2 x i1> @t15_vec_x_is_one_or_zero(<2 x i64> %y, <2 x i32> %len) {
 ; CHECK-LABEL: @t15_vec_x_is_one_or_zero(
-; CHECK-NEXT:    [[T0:%.*]] = sub <2 x i32> <i32 64, i32 64>, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl <2 x i32> <i32 1, i32 0>, [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add <2 x i32> [[LEN]], <i32 -16, i32 -16>
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext <2 x i32> [[T2]] to <2 x i64>
-; CHECK-NEXT:    [[T3:%.*]] = lshr <2 x i64> [[Y:%.*]], [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc <2 x i64> [[T3]] to <2 x i32>
-; CHECK-NEXT:    [[T4:%.*]] = and <2 x i32> [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne <2 x i32> [[T4]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr <2 x i64> [[Y:%.*]], <i64 48, i64 48>
+; CHECK-NEXT:    [[TMP2:%.*]] = and <2 x i64> [[TMP1]], <i64 1, i64 0>
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne <2 x i64> [[TMP2]], zeroinitializer
+; CHECK-NEXT:    ret <2 x i1> [[TMP3]]
 ;
   %t0 = sub <2 x i32> <i32 64, i32 64>, %len
   %t1 = shl <2 x i32> <i32 1, i32 0>, %t0
   %t2 = add <2 x i32> %len, <i32 -16, i32 -16>
   %t2_wide = zext <2 x i32> %t2 to <2 x i64>
   %t3 = lshr <2 x i64> %y, %t2_wide
   %t3_trunc = trunc <2 x i64> %t3 to <2 x i32>
   %t4 = and <2 x i32> %t1, %t3_trunc
   %t5 = icmp ne <2 x i32> %t4, <i32 0, i32 0>
   ret <2 x i1> %t5
 }
 define <2 x i1> @t16_vec_y_is_one_or_zero(<2 x i32> %x, <2 x i32> %len) {
 ; CHECK-LABEL: @t16_vec_y_is_one_or_zero(
-; CHECK-NEXT:    [[T0:%.*]] = sub <2 x i32> <i32 64, i32 64>, [[LEN:%.*]]
-; CHECK-NEXT:    [[T1:%.*]] = shl <2 x i32> [[X:%.*]], [[T0]]
-; CHECK-NEXT:    [[T2:%.*]] = add <2 x i32> [[LEN]], <i32 -16, i32 -16>
-; CHECK-NEXT:    [[T2_WIDE:%.*]] = zext <2 x i32> [[T2]] to <2 x i64>
-; CHECK-NEXT:    [[T3:%.*]] = lshr <2 x i64> <i64 1, i64 0>, [[T2_WIDE]]
-; CHECK-NEXT:    [[T3_TRUNC:%.*]] = trunc <2 x i64> [[T3]] to <2 x i32>
-; CHECK-NEXT:    [[T4:%.*]] = and <2 x i32> [[T1]], [[T3_TRUNC]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne <2 x i32> [[T4]], zeroinitializer
-; CHECK-NEXT:    ret <2 x i1> [[T5]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %t0 = sub <2 x i32> <i32 64, i32 64>, %len
   %t1 = shl <2 x i32> %x, %t0
   %t2 = add <2 x i32> %len, <i32 -16, i32 -16>
   %t2_wide = zext <2 x i32> %t2 to <2 x i64>
   %t3 = lshr <2 x i64> <i64 1, i64 0>, %t2_wide
   %t3_trunc = trunc <2 x i64> %t3 to <2 x i32>
   %t4 = and <2 x i32> %t1, %t3_trunc
   %t5 = icmp ne <2 x i32> %t4, <i32 0, i32 0>
   ret <2 x i1> %t5
 }
 
 ;------------------------------------------------------------------------------;
 
 ; All other tests - extra uses, etc are already covered in
 ; shift-amount-reassociation-in-bittest-with-truncation-shl.ll and
 ; shift-amount-reassociation-in-bittest.ll
 
 ; And that's the main motivational pattern:
 define i1 @rawspeed_signbit(i64 %storage, i32 %nbits) {
 ; CHECK-LABEL: @rawspeed_signbit(
-; CHECK-NEXT:    [[SKIPNBITS:%.*]] = sub nsw i32 64, [[NBITS:%.*]]
-; CHECK-NEXT:    [[SKIPNBITSWIDE:%.*]] = zext i32 [[SKIPNBITS]] to i64
-; CHECK-NEXT:    [[DATAWIDE:%.*]] = lshr i64 [[STORAGE:%.*]], [[SKIPNBITSWIDE]]
-; CHECK-NEXT:    [[DATA:%.*]] = trunc i64 [[DATAWIDE]] to i32
-; CHECK-NEXT:    [[NBITSMINUSONE:%.*]] = add nsw i32 [[NBITS]], -1
-; CHECK-NEXT:    [[BITMASK:%.*]] = shl i32 1, [[NBITSMINUSONE]]
-; CHECK-NEXT:    [[BITMASKED:%.*]] = and i32 [[BITMASK]], [[DATA]]
-; CHECK-NEXT:    [[ISBITUNSET:%.*]] = icmp eq i32 [[BITMASKED]], 0
-; CHECK-NEXT:    ret i1 [[ISBITUNSET]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i64 [[STORAGE:%.*]], -1
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %skipnbits = sub nsw i32 64, %nbits
   %skipnbitswide = zext i32 %skipnbits to i64
   %datawide = lshr i64 %storage, %skipnbitswide
   %data = trunc i64 %datawide to i32
   %nbitsminusone = add nsw i32 %nbits, -1
   %bitmask = shl i32 1, %nbitsminusone
   %bitmasked = and i32 %bitmask, %data
   %isbitunset = icmp eq i32 %bitmasked, 0
   ret i1 %isbitunset
 }

llvm/test/Transforms/InstCombine/shift-amount-reassociation-in-bittest-with-truncation-shl.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt %s -instcombine -S | FileCheck %s
 
 ; Given pattern:
 ;   icmp eq/ne (and ((x shift Q), (y oppositeshift K))), 0
 ; we should move shifts to the same hand of 'and', i.e. e.g. rewrite as
 ;   icmp eq/ne (and (((x shift Q) shift K), y)), 0
 ; We are only interested in opposite logical shifts here.
-; We still can handle the case where there is a truncation between a shift
-; and an 'and', but for now only if it's 'shl' - simpler legality check.
+; We still can handle the case where there is a truncation between a shift and
+; an 'and'. If it's trunc-of-shl - no extra legality check is needed.
 
 ;-------------------------------------------------------------------------------
 ; Basic scalar tests
 ;-------------------------------------------------------------------------------
 
 define i1 @t0_const_after_fold_lshr_shl_ne(i32 %x, i64 %y, i32 %len) {
 ; CHECK-LABEL: @t0_const_after_fold_lshr_shl_ne(
 ; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[X:%.*]], 31