[NFC][SCEV] Add tests related to bit masking (PR37793)

[lebedev.ri]

Summary

Related to https://bugs.llvm.org/show_bug.cgi?id=37793, https://reviews.llvm.org/D46760#1127287

We'd like to do this canonicalization https://rise4fun.com/Alive/Gmc
But it is currently restricted by rL155136 / rL155362, which says:

// This is a constant shift of a constant shift. Be careful about hiding
// shl instructions behind bit masks. They are used to represent multiplies
// by a constant, and it is important that simple arithmetic expressions
// are still recognizable by scalar evolution.
//
// The transforms applied to shl are very similar to the transforms applied
// to mul by constant. We can be more aggressive about optimizing right
// shifts.
//
// Combinations of right and left shifts will still be optimized in
// DAGCombine where scalar evolution no longer applies.

I think these tests show that for *constants*, SCEV has no issues with that canonicalization.

[lebedev.ri]

test/Analysis/ScalarEvolution/lshr-shl-differentconstmask.ll

45–46

@spatel BTW, how do we want to canonicalize it? https://rise4fun.com/Alive/mxm

73–74

Similarly, mask first or last? https://rise4fun.com/Alive/0X9

[efriedma]

test/Analysis/ScalarEvolution/lshr-shl-differentconstmask.ll

45–46

DAGCombine currently canonicalizes to srl+and. Unless there's a compelling reason to choose something else, that seems fine.

[lebedev.ri]

test/Analysis/ScalarEvolution/lshr-shl-differentconstmask.ll

45–46

Aha, instcombine actually transforms it so that and is last.
https://godbolt.org/g/3cM8D7 (at least for some masks.)
Ok, that answers it.

[lebedev.ri]

Actually drop the no-longer-valid comment.

[spatel]

lib/Transforms/InstCombine/InstCombineShifts.cpp

625–629

Better to just add a 'FIXME' note until we actually make the code change here to ignore 'exact'?

[lebedev.ri]

lib/Transforms/InstCombine/InstCombineShifts.cpp

625–629

Yes, indeed. Will add.

[lebedev.ri]

Add new comment in place of the one being deleted.

lib/Transforms/InstCombine/InstCombineShifts.cpp

625–629

Hopefully this is better.

[mkazantsev]

LGTM

[lebedev.ri]

In D48229#1137346, @mkazantsev wrote:

LGTM

Thank you for the review!

lib/Transforms/InstCombine/InstCombineShifts.cpp

625

This obviously should be // FIXME: we do not yet transform non-exact shr's. The backend (DAGCombine)
Will fix before commit.

lib/Transforms/InstCombine/InstCombineShifts.cpp

if (match(Op1, m_APInt(ShAmtAPInt))) {
     }
 
     // (X >> C) << C --> X & (-1 << C)
     if (match(Op0, m_Shr(m_Value(X), m_Specific(Op1)))) {
       APInt Mask(APInt::getHighBitsSet(BitWidth, BitWidth - ShAmt));
       return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
     }
 
-    // Be careful about hiding shl instructions behind bit masks. They are used
-    // to represent multiplies by a constant, and it is important that simple
-    // arithmetic expressions are still recognizable by scalar evolution.
-    // The inexact versions are deferred to DAGCombine, so we don't hide shl
-    // behind a bit mask.
+    // FIXME: we do not yet transform non-exact lshr's. The backend (DAGCombine)
+    // needs a few fixes for the rotate pattern recognition first.
     const APInt *ShOp1;
     if (match(Op0, m_Exact(m_Shr(m_Value(X), m_APInt(ShOp1))))) {
       unsigned ShrAmt = ShOp1->getZExtValue();
       if (ShrAmt < ShAmt) {
         // If C1 < C2: (X >>?,exact C1) << C2 --> X << (C2 - C1)
         Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShrAmt);
         auto *NewShl = BinaryOperator::CreateShl(X, ShiftDiff);
         NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());

test/Analysis/ScalarEvolution/extract-highbits-sameconstmask.ll

+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
+
+; The obvious case.
+define i32 @div(i32 %val) nounwind {
+; CHECK-LABEL: 'div'
+; CHECK-NEXT:  Classifying expressions for: @div
+; CHECK-NEXT:    %tmp1 = udiv i32 %val, 16
+; CHECK-NEXT:    --> (%val /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT:    %tmp2 = mul i32 %tmp1, 16
+; CHECK-NEXT:    --> (16 * (%val /u 16))<nuw> U: [0,-15) S: [0,-15)
+; CHECK-NEXT:  Determining loop execution counts for: @div
+;
+  %tmp1 = udiv i32 %val, 16
+  %tmp2 = mul i32 %tmp1, 16
+  ret i32 %tmp2
+}
+
+define i32 @sdiv(i32 %val) nounwind {
+; CHECK-LABEL: 'sdiv'
+; CHECK-NEXT:  Classifying expressions for: @sdiv
+; CHECK-NEXT:    %tmp1 = sdiv i32 %val, 16
+; CHECK-NEXT:    --> %tmp1 U: full-set S: [-134217728,134217728)
+; CHECK-NEXT:    %tmp2 = mul i32 %tmp1, 16
+; CHECK-NEXT:    --> (16 * %tmp1) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:  Determining loop execution counts for: @sdiv
+;
+  %tmp1 = sdiv i32 %val, 16
+  %tmp2 = mul i32 %tmp1, 16
+  ret i32 %tmp2
+}
+
+; Or, it could be a number of equivalent patterns with mask:
+;   b) x &  (-1 << nbits)
+;   d) x >> nbits << nbits
+
+define i32 @mask_b(i32 %val) nounwind {
+; CHECK-LABEL: 'mask_b'
+; CHECK-NEXT:  Classifying expressions for: @mask_b
+; CHECK-NEXT:    %masked = and i32 %val, -16
+; CHECK-NEXT:    --> (16 * (%val /u 16))<nuw> U: [0,-15) S: [0,-15)
+; CHECK-NEXT:  Determining loop execution counts for: @mask_b
+;
+  %masked = and i32 %val, -16
+  ret i32 %masked
+}
+
+define i32 @mask_d(i32 %val) nounwind {
+; CHECK-LABEL: 'mask_d'
+; CHECK-NEXT:  Classifying expressions for: @mask_d
+; CHECK-NEXT:    %lowbitscleared = lshr i32 %val, 4
+; CHECK-NEXT:    --> (%val /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT:    %masked = shl i32 %lowbitscleared, 4
+; CHECK-NEXT:    --> (16 * (%val /u 16))<nuw> U: [0,-15) S: [0,-15)
+; CHECK-NEXT:  Determining loop execution counts for: @mask_d
+;
+  %lowbitscleared = lshr i32 %val, 4
+  %masked = shl i32 %lowbitscleared, 4
+  ret i32 %masked
+}

test/Analysis/ScalarEvolution/extract-highbits-variablemask.ll

+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
+
+; These testcases aren't *identical* but they have the same/similar meaning.
+
+; The obvious case.
+define i32 @div(i32 %val, i32 %num) nounwind {
+; CHECK-LABEL: 'div'
+; CHECK-NEXT:  Classifying expressions for: @div
+; CHECK-NEXT:    %tmp1 = udiv i32 %val, %num
+; CHECK-NEXT:    --> (%val /u %num) U: full-set S: full-set
+; CHECK-NEXT:    %tmp2 = mul i32 %tmp1, %num
+; CHECK-NEXT:    --> ((%val /u %num) * %num) U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @div
+;
+  %tmp1 = udiv i32 %val, %num
+  %tmp2 = mul i32 %tmp1, %num
+  ret i32 %tmp2
+}
+
+define i32 @sdiv(i32 %val, i32 %num) nounwind {
+; CHECK-LABEL: 'sdiv'
+; CHECK-NEXT:  Classifying expressions for: @sdiv
+; CHECK-NEXT:    %tmp1 = sdiv i32 %val, %num
+; CHECK-NEXT:    --> %tmp1 U: full-set S: full-set
+; CHECK-NEXT:    %tmp2 = mul i32 %tmp1, %num
+; CHECK-NEXT:    --> (%num * %tmp1) U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @sdiv
+;
+  %tmp1 = sdiv i32 %val, %num
+  %tmp2 = mul i32 %tmp1, %num
+  ret i32 %tmp2
+}
+
+; Or, it could be a number of equivalent patterns with mask:
+;   b) x &  (-1 << nbits)
+;   d) x >> (32 - y) << (32 - y)
+
+define i32 @mask_b(i32 %val, i32 %numlowbits) nounwind {
+; CHECK-LABEL: 'mask_b'
+; CHECK-NEXT:  Classifying expressions for: @mask_b
+; CHECK-NEXT:    %mask = shl i32 -1, %numlowbits
+; CHECK-NEXT:    --> %mask U: full-set S: full-set
+; CHECK-NEXT:    %masked = and i32 %mask, %val
+; CHECK-NEXT:    --> %masked U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @mask_b
+;
+  %mask = shl i32 -1, %numlowbits
+  %masked = and i32 %mask, %val
+  ret i32 %masked
+}
+
+define i32 @mask_d(i32 %val, i32 %lowbits) nounwind {
+; CHECK-LABEL: 'mask_d'
+; CHECK-NEXT:  Classifying expressions for: @mask_d
+; CHECK-NEXT:    %numlowbits = sub i32 32, %lowbits
+; CHECK-NEXT:    --> (32 + (-1 * %lowbits)) U: full-set S: full-set
+; CHECK-NEXT:    %lowbitscleared = lshr i32 %val, %numlowbits
+; CHECK-NEXT:    --> %lowbitscleared U: full-set S: full-set
+; CHECK-NEXT:    %masked = shl i32 %lowbitscleared, %numlowbits
+; CHECK-NEXT:    --> %masked U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @mask_d
+;
+  %numlowbits = sub i32 32, %lowbits
+  %lowbitscleared = lshr i32 %val, %numlowbits
+  %masked = shl i32 %lowbitscleared, %numlowbits
+  ret i32 %masked
+}

test/Analysis/ScalarEvolution/extract-lowbits-sameconstmask.ll

+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
+
+; The obvious case.
+define i32 @mul(i32 %val) nounwind {
+; CHECK-LABEL: 'mul'
+; CHECK-NEXT:  Classifying expressions for: @mul
+; CHECK-NEXT:    %tmp1 = mul i32 %val, 16
+; CHECK-NEXT:    --> (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %tmp2 = udiv i32 %tmp1, 16
+; CHECK-NEXT:    --> ((16 * %val) /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @mul
+;
+  %tmp1 = mul i32 %val, 16
+  %tmp2 = udiv i32 %tmp1, 16
+  ret i32 %tmp2
+}
+
+; Or, it could be any number of equivalent patterns with mask:
+;   a) x &  (1 << nbits) - 1
+;   b) x & ~(-1 << nbits)
+;   c) x &  (-1 >> (32 - y))
+;   d) x << (32 - y) >> (32 - y)
+
+define i32 @mask_abc(i32 %val) nounwind {
+; CHECK-LABEL: 'mask_abc'
+; CHECK-NEXT:  Classifying expressions for: @mask_abc
+; CHECK-NEXT:    %masked = and i32 %val, 15
+; CHECK-NEXT:    --> (zext i4 (trunc i32 %val to i4) to i32) U: [0,16) S: [0,16)
+; CHECK-NEXT:  Determining loop execution counts for: @mask_abc
+;
+  %masked = and i32 %val, 15
+  ret i32 %masked
+}
+
+define i32 @mask_d(i32 %val) nounwind {
+; CHECK-LABEL: 'mask_d'
+; CHECK-NEXT:  Classifying expressions for: @mask_d
+; CHECK-NEXT:    %highbitscleared = shl i32 %val, 4
+; CHECK-NEXT:    --> (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %masked = lshr i32 %highbitscleared, 4
+; CHECK-NEXT:    --> ((16 * %val) /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @mask_d
+;
+  %highbitscleared = shl i32 %val, 4
+  %masked = lshr i32 %highbitscleared, 4
+  ret i32 %masked
+}

test/Analysis/ScalarEvolution/extract-lowbits-variablemask.ll

+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
+
+; These testcases aren't *identical* but they have the same/similar meaning.
+
+; The obvious case.
+define i32 @mul(i32 %val, i32 %num) nounwind {
+; CHECK-LABEL: 'mul'
+; CHECK-NEXT:  Classifying expressions for: @mul
+; CHECK-NEXT:    %tmp1 = mul i32 %val, %num
+; CHECK-NEXT:    --> (%val * %num) U: full-set S: full-set
+; CHECK-NEXT:    %tmp2 = udiv i32 %tmp1, %num
+; CHECK-NEXT:    --> ((%val * %num) /u %num) U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @mul
+;
+  %tmp1 = mul i32 %val, %num
+  %tmp2 = udiv i32 %tmp1, %num
+  ret i32 %tmp2
+}
+
+; Or, it could be any number of equivalent patterns with mask:
+;   a) x &  (1 << nbits) - 1
+;   b) x & ~(-1 << nbits)
+;   c) x &  (-1 >> (32 - y))
+;   d) x << (32 - y) >> (32 - y)
+
+define i32 @mask_a(i32 %val, i32 %numlowbits) nounwind {
+; CHECK-LABEL: 'mask_a'
+; CHECK-NEXT:  Classifying expressions for: @mask_a
+; CHECK-NEXT:    %onebit = shl i32 1, %numlowbits
+; CHECK-NEXT:    --> %onebit U: full-set S: full-set
+; CHECK-NEXT:    %mask = add nsw i32 %onebit, -1
+; CHECK-NEXT:    --> (-1 + %onebit) U: full-set S: full-set
+; CHECK-NEXT:    %masked = and i32 %mask, %val
+; CHECK-NEXT:    --> %masked U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @mask_a
+;
+  %onebit = shl i32 1, %numlowbits
+  %mask = add nsw i32 %onebit, -1
+  %masked = and i32 %mask, %val
+  ret i32 %masked
+}
+
+define i32 @mask_b(i32 %val, i32 %numlowbits) nounwind {
+; CHECK-LABEL: 'mask_b'
+; CHECK-NEXT:  Classifying expressions for: @mask_b
+; CHECK-NEXT:    %notmask = shl i32 -1, %numlowbits
+; CHECK-NEXT:    --> %notmask U: full-set S: full-set
+; CHECK-NEXT:    %mask = xor i32 %notmask, -1
+; CHECK-NEXT:    --> (-1 + (-1 * %notmask)) U: full-set S: full-set
+; CHECK-NEXT:    %masked = and i32 %mask, %val
+; CHECK-NEXT:    --> %masked U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @mask_b
+;
+  %notmask = shl i32 -1, %numlowbits
+  %mask = xor i32 %notmask, -1
+  %masked = and i32 %mask, %val
+  ret i32 %masked
+}
+
+define i32 @mask_c(i32 %val, i32 %numlowbits) nounwind {
+; CHECK-LABEL: 'mask_c'
+; CHECK-NEXT:  Classifying expressions for: @mask_c
+; CHECK-NEXT:    %numhighbits = sub i32 32, %numlowbits
+; CHECK-NEXT:    --> (32 + (-1 * %numlowbits)) U: full-set S: full-set
+; CHECK-NEXT:    %mask = lshr i32 -1, %numhighbits
+; CHECK-NEXT:    --> %mask U: full-set S: full-set
+; CHECK-NEXT:    %masked = and i32 %mask, %val
+; CHECK-NEXT:    --> %masked U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @mask_c
+;
+  %numhighbits = sub i32 32, %numlowbits
+  %mask = lshr i32 -1, %numhighbits
+  %masked = and i32 %mask, %val
+  ret i32 %masked
+}
+
+define i32 @mask_d(i32 %val, i32 %numlowbits) nounwind {
+; CHECK-LABEL: 'mask_d'
+; CHECK-NEXT:  Classifying expressions for: @mask_d
+; CHECK-NEXT:    %numhighbits = sub i32 32, %numlowbits
+; CHECK-NEXT:    --> (32 + (-1 * %numlowbits)) U: full-set S: full-set
+; CHECK-NEXT:    %highbitscleared = shl i32 %val, %numhighbits
+; CHECK-NEXT:    --> %highbitscleared U: full-set S: full-set
+; CHECK-NEXT:    %masked = lshr i32 %highbitscleared, %numhighbits
+; CHECK-NEXT:    --> %masked U: full-set S: full-set
+; CHECK-NEXT:  Determining loop execution counts for: @mask_d
+;
+  %numhighbits = sub i32 32, %numlowbits
+  %highbitscleared = shl i32 %val, %numhighbits
+  %masked = lshr i32 %highbitscleared, %numhighbits
+  ret i32 %masked
+}

test/Analysis/ScalarEvolution/lshr-shl-differentconstmask.ll

+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
+
+; The obvious case.
+define i32 @udiv_biggerLshr(i32 %val) nounwind {
+; CHECK-LABEL: 'udiv_biggerLshr'
+; CHECK-NEXT:  Classifying expressions for: @udiv_biggerLshr
+; CHECK-NEXT:    %tmp1 = udiv i32 %val, 64
+; CHECK-NEXT:    --> (%val /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:    %tmp2 = mul i32 %tmp1, 16
+; CHECK-NEXT:    --> (16 * (%val /u 64))<nuw> U: [0,1073741809) S: [0,1073741809)
+; CHECK-NEXT:  Determining loop execution counts for: @udiv_biggerLshr
+;
+  %tmp1 = udiv i32 %val, 64
+  %tmp2 = mul i32 %tmp1, 16
+  ret i32 %tmp2
+}
+
+define i32 @udiv_biggerShl(i32 %val) nounwind {
+; CHECK-LABEL: 'udiv_biggerShl'
+; CHECK-NEXT:  Classifying expressions for: @udiv_biggerShl
+; CHECK-NEXT:    %tmp1 = udiv i32 %val, 16
+; CHECK-NEXT:    --> (%val /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT:    %tmp2 = mul i32 %tmp1, 64
+; CHECK-NEXT:    --> (64 * (%val /u 16))<nuw> U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:  Determining loop execution counts for: @udiv_biggerShl
+;
+  %tmp1 = udiv i32 %val, 16
+  %tmp2 = mul i32 %tmp1, 64
+  ret i32 %tmp2
+}
+
+; Or, it could have been transformed to shifts
+
+define i32 @shifty_biggerLshr(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerLshr'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerLshr
+; CHECK-NEXT:    %tmp1 = lshr i32 %val, 6
+; CHECK-NEXT:    --> (%val /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:    %tmp2 = shl i32 %tmp1, 4
+; CHECK-NEXT:    --> (16 * (%val /u 64))<nuw> U: [0,1073741809) S: [0,1073741809)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerLshr
+;
+  %tmp1 = lshr i32 %val, 6
+  %tmp2 = shl i32 %tmp1, 4
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerLshr_lshrexact(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerLshr_lshrexact'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerLshr_lshrexact
+; CHECK-NEXT:    %tmp1 = lshr exact i32 %val, 6
+; CHECK-NEXT:    --> (%val /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:    %tmp2 = shl i32 %tmp1, 4
+; CHECK-NEXT:    --> (16 * (%val /u 64))<nuw> U: [0,1073741809) S: [0,1073741809)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerLshr_lshrexact
+;
+  %tmp1 = lshr exact i32 %val, 6
+  %tmp2 = shl i32 %tmp1, 4
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerShr(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerShr'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerShr
+; CHECK-NEXT:    %tmp1 = lshr i32 %val, 4
+; CHECK-NEXT:    --> (%val /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT:    %tmp2 = shl i32 %tmp1, 6
+; CHECK-NEXT:    --> (64 * (%val /u 16))<nuw> U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerShr
+;
+  %tmp1 = lshr i32 %val, 4
+  %tmp2 = shl i32 %tmp1, 6
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerShr_lshrexact(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerShr_lshrexact'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerShr_lshrexact
+; CHECK-NEXT:    %tmp1 = lshr exact i32 %val, 4
+; CHECK-NEXT:    --> (%val /u 16) U: [0,268435456) S: [0,268435456)
+; CHECK-NEXT:    %tmp2 = shl i32 %tmp1, 6
+; CHECK-NEXT:    --> (64 * (%val /u 16))<nuw> U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerShr_lshrexact
+;
+  %tmp1 = lshr exact i32 %val, 4
+  %tmp2 = shl i32 %tmp1, 6
+  ret i32 %tmp2
+}
+
+; Or, further folded into mask variant.
+
+define i32 @masky_biggerLshr(i32 %val) {
+; CHECK-LABEL: 'masky_biggerLshr'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerLshr
+; CHECK-NEXT:    %tmp1 = lshr i32 %val, 2
+; CHECK-NEXT:    --> (%val /u 4) U: [0,1073741824) S: [0,1073741824)
+; CHECK-NEXT:    %tmp2 = and i32 %tmp1, -16
+; CHECK-NEXT:    --> (16 * (%val /u 64))<nuw> U: [0,1073741809) S: [0,1073741809)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerLshr
+;
+  %tmp1 = lshr i32 %val, 2
+  %tmp2 = and i32 %tmp1, -16
+  ret i32 %tmp2
+}
+
+define i32 @masky_biggerLshr_lshrexact(i32 %val) {
+; CHECK-LABEL: 'masky_biggerLshr_lshrexact'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerLshr_lshrexact
+; CHECK-NEXT:    %tmp1 = lshr exact i32 %val, 2
+; CHECK-NEXT:    --> (%val /u 4) U: [0,1073741824) S: [0,1073741824)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerLshr_lshrexact
+;
+  %tmp1 = lshr exact i32 %val, 2
+  ret i32 %tmp1
+}
+
+define i32 @masky_biggerShr(i32 %val) {
+; CHECK-LABEL: 'masky_biggerShr'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerShr
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 2
+; CHECK-NEXT:    --> (4 * %val) U: [0,-3) S: [-2147483648,2147483645)
+; CHECK-NEXT:    %tmp2 = and i32 %tmp1, -64
+; CHECK-NEXT:    --> (64 * (zext i26 (trunc i32 (%val /u 16) to i26) to i32))<nuw> U: [0,-63) S: [0,-63)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerShr
+;
+  %tmp1 = shl i32 %val, 2
+  %tmp2 = and i32 %tmp1, -64
+  ret i32 %tmp2
+}
+
+define i32 @masky_biggerShr_lshrexact(i32 %val) {
+; CHECK-LABEL: 'masky_biggerShr_lshrexact'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerShr_lshrexact
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 2
+; CHECK-NEXT:    --> (4 * %val) U: [0,-3) S: [-2147483648,2147483645)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerShr_lshrexact
+;
+  %tmp1 = shl i32 %val, 2
+  ret i32 %tmp1
+}

test/Analysis/ScalarEvolution/shl-lshr-differentconstmask.ll

+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -S -analyze -scalar-evolution < %s | FileCheck %s
+
+; The obvious case.
+define i32 @mul_biggerShl(i32 %val) nounwind {
+; CHECK-LABEL: 'mul_biggerShl'
+; CHECK-NEXT:  Classifying expressions for: @mul_biggerShl
+; CHECK-NEXT:    %tmp1 = mul i32 %val, 64
+; CHECK-NEXT:    --> (64 * %val) U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:    %tmp2 = udiv i32 %tmp1, 16
+; CHECK-NEXT:    --> ((64 * %val) /u 16) U: [0,268435453) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @mul_biggerShl
+;
+  %tmp1 = mul i32 %val, 64
+  %tmp2 = udiv i32 %tmp1, 16
+  ret i32 %tmp2
+}
+
+define i32 @mul_biggerLshl(i32 %val) nounwind {
+; CHECK-LABEL: 'mul_biggerLshl'
+; CHECK-NEXT:  Classifying expressions for: @mul_biggerLshl
+; CHECK-NEXT:    %tmp1 = mul i32 %val, 16
+; CHECK-NEXT:    --> (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %tmp2 = udiv i32 %tmp1, 64
+; CHECK-NEXT:    --> ((16 * %val) /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @mul_biggerLshl
+;
+  %tmp1 = mul i32 %val, 16
+  %tmp2 = udiv i32 %tmp1, 64
+  ret i32 %tmp2
+}
+
+; Or, it could have been transformed to shifts
+
+define i32 @shifty_biggerShl(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerShl'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerShl
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 6
+; CHECK-NEXT:    --> (64 * %val) U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 4
+; CHECK-NEXT:    --> ((64 * %val) /u 16) U: [0,268435453) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerShl
+;
+  %tmp1 = shl i32 %val, 6
+  %tmp2 = lshr i32 %tmp1, 4
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerShl_shlnuw(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerShl_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerShl_shlnuw
+; CHECK-NEXT:    %tmp1 = shl nuw i32 %val, 6
+; CHECK-NEXT:    --> (64 * %val) U: [0,-63) S: [-2147483648,2147483585)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 4
+; CHECK-NEXT:    --> ((64 * %val) /u 16) U: [0,268435453) S: [0,268435456)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerShl_shlnuw
+;
+  %tmp1 = shl nuw i32 %val, 6
+  %tmp2 = lshr i32 %tmp1, 4
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerLshr(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerLshr'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerLshr
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 4
+; CHECK-NEXT:    --> (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 6
+; CHECK-NEXT:    --> ((16 * %val) /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerLshr
+;
+  %tmp1 = shl i32 %val, 4
+  %tmp2 = lshr i32 %tmp1, 6
+  ret i32 %tmp2
+}
+
+define i32 @shifty_biggerLshr_shlnuw(i32 %val) {
+; CHECK-LABEL: 'shifty_biggerLshr_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @shifty_biggerLshr_shlnuw
+; CHECK-NEXT:    %tmp1 = shl nuw i32 %val, 4
+; CHECK-NEXT:    --> (16 * %val) U: [0,-15) S: [-2147483648,2147483633)
+; CHECK-NEXT:    %tmp2 = lshr i32 %tmp1, 6
+; CHECK-NEXT:    --> ((16 * %val) /u 64) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @shifty_biggerLshr_shlnuw
+;
+  %tmp1 = shl nuw i32 %val, 4
+  %tmp2 = lshr i32 %tmp1, 6
+  ret i32 %tmp2
+}
+
+; Or, further folded into mask variant.
+
+define i32 @masky_biggerShl(i32 %val) {
+; CHECK-LABEL: 'masky_biggerShl'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerShl
+; CHECK-NEXT:    %tmp1 = shl i32 %val, 2
+; CHECK-NEXT:    --> (4 * %val) U: [0,-3) S: [-2147483648,2147483645)
+; CHECK-NEXT:    %tmp2 = and i32 %tmp1, 268435452
+; CHECK-NEXT:    --> (4 * (zext i26 (trunc i32 %val to i26) to i32))<nuw> U: [0,268435453) S: [0,268435453)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerShl
+;
+  %tmp1 = shl i32 %val, 2
+  %tmp2 = and i32 %tmp1, 268435452
+  ret i32 %tmp2
+}
+
+define i32 @masky_biggerShl_shlnuw(i32 %val) {
+; CHECK-LABEL: 'masky_biggerShl_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerShl_shlnuw
+; CHECK-NEXT:    %tmp1 = shl nuw i32 %val, 2
+; CHECK-NEXT:    --> (4 * %val) U: [0,-3) S: [-2147483648,2147483645)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerShl_shlnuw
+;
+  %tmp1 = shl nuw i32 %val, 2
+  ret i32 %tmp1
+}
+
+define i32 @masky_biggerLshr(i32 %val) {
+; CHECK-LABEL: 'masky_biggerLshr'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerLshr
+; CHECK-NEXT:    %tmp1 = lshr i32 %val, 2
+; CHECK-NEXT:    --> (%val /u 4) U: [0,1073741824) S: [0,1073741824)
+; CHECK-NEXT:    %tmp2 = and i32 %tmp1, 67108863
+; CHECK-NEXT:    --> (zext i26 (trunc i32 (%val /u 4) to i26) to i32) U: [0,67108864) S: [0,67108864)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerLshr
+;
+  %tmp1 = lshr i32 %val, 2
+  %tmp2 = and i32 %tmp1, 67108863
+  ret i32 %tmp2
+}
+
+define i32 @masky_biggerLshr_shlnuw(i32 %val) {
+; CHECK-LABEL: 'masky_biggerLshr_shlnuw'
+; CHECK-NEXT:  Classifying expressions for: @masky_biggerLshr_shlnuw
+; CHECK-NEXT:    %tmp1 = lshr i32 %val, 2
+; CHECK-NEXT:    --> (%val /u 4) U: [0,1073741824) S: [0,1073741824)
+; CHECK-NEXT:  Determining loop execution counts for: @masky_biggerLshr_shlnuw
+;
+  %tmp1 = lshr i32 %val, 2
+  ret i32 %tmp1
+}