[InstSimplify] Fold (ctpop(X) == N) || (X != 0) into X != 0 where N > 0

[hkmatsumoto]

Summary

(ctpop(X) == N) || (X != 0) --> (X != 0) https://alive2.llvm.org/ce/z/hYL5C2 (for N = 10)
(ctpop(X) != N) && (X == 0) --> (X == 0) https://alive2.llvm.org/ce/z/oLkMvI (for N = 15)

[hkmatsumoto]

Proof (This is first time writing proof in English, so sorry for any inconveniences)
Suppose X: i32

1. For 0 < N <= 32
   • ctpop(X) == N --> X > 0.
   • Hence (ctpop(X) == N) || (X != 0) --> X > 0 || X != 0.
   • Intuitively X > 0 || X != 0 --> X != 0.
2. For 32 < N (This case is already optimized anyway)
   • ctpop(X) == N is always false, because of the semantics of ctpop().
   • Hence (ctpop(X) == N) || (X != 0) --> false || X != 0 --> X != 0.

[spatel]

If we are not creating a new value in a transformation (only returning an existing value or constant), we usually prefer to add that fold (and tests) to "InstSimplify".

Note that you can use "llvm.assume" with Alive2 to create a more general proof instead of using a specific constant:
https://alive2.llvm.org/ce/z/vcY7_s

[hkmatsumoto]

• Move change and its test to InstSimplify

• Remove/unchange tests whose and/or are replaced with select

This is because InstSimlify/and-or-icmp-* tests do not include such tests, and as far as I tried on goldbot.org simplifyAndOrOfICmps* functions in InstructionSimplify.cpp does not acknowledge select operands to optimize.

[spatel]

llvm/lib/Analysis/InstructionSimplify.cpp

1811

Normally in this kind of code, we name this "C" (for constant).

1814

Use m_ZeroInt() instead of m_SpecificInt()?

1815

It seems more natural if we write this as "!C->isZero()"

llvm/test/Transforms/InstCombine/ispow2.ll

900 ↗

(On Diff #419469)

We should add a new test for "wrong predicate" because this test and the later one are reduced before we reach the transform in InstCombine.

llvm/test/Transforms/InstSimplify/and-or-icmp-ctpop.ll

35

Should this be or <2 x i1> %cmp, %notzero?

[spatel]

I posted inline comments on this patch yesterday, but it did not appear to trigger an email.

[hkmatsumoto]

Oops, sorry I actually got the email but was hidden under a bunch of others.
Let me quickly address some of your reviews, and address all of them tomorrow morning.

[hkmatsumoto]

Address code reviews

[spatel]

In D122757#3422764, @hkmatsumoto wrote:

Oops, sorry I actually got the email but was hidden under a bunch of others.
Let me quickly address some of your reviews, and address all of them tomorrow morning.

Ah - I actually see the mail too now, but it was also buried in my inbox. :)

Thanks for the updates. I think you can request commit access now if you have not already:
https://llvm.org/docs/DeveloperPolicy.html#obtaining-commit-access

If you get that, you can add the new tests as an "NFC" patch first. After that, this patch should be good to commit too.

[hkmatsumoto]

Update negative tests

[hkmatsumoto]

I pre-committed tests but immediately reverted as I noticed I forgot to rerun update_test_checks.py to make them baseline tests.
Let me take some time to confirm that the revert commit (rGf65c78a0949023bb0f3051cdaea7758e48420978) made CI pass.

[hkmatsumoto]

Sync with main branch

[spatel]

LGTM

llvm/lib/Analysis/InstructionSimplify.cpp

static Value *simplifyAndOrOfICmpsWithLimitConst(ICmpInst *Cmp0, ICmpInst *Cmp1,
   // (X == MIN) || (X <= Y) --> X <= Y
   if (MinMaxC.isMinValue())
     if (Pred0 == ICmpInst::ICMP_NE && Pred1 == ICmpInst::ICMP_UGT)
       return Cmp1;
 
   return nullptr;
 }
 
+/// Try to simplify and/or of icmp with ctpop intrinsic.
+static Value *simplifyAndOrOfICmpsWithCtpop(ICmpInst *Cmp0, ICmpInst *Cmp1,
+                                            bool IsAnd) {
+  ICmpInst::Predicate Pred0, Pred1;
+  Value *X;
+  const APInt *C;
+  if (!match(Cmp0, m_ICmp(Pred0, m_Intrinsic<Intrinsic::ctpop>(m_Value(X)),
+                          m_APInt(C))) ||
+      !match(Cmp1, m_ICmp(Pred1, m_Specific(X), m_ZeroInt())) || C->isZero())
+    return nullptr;
+
+  // (ctpop(X) == C) || (X != 0) --> X != 0 where C > 0
+  if (!IsAnd && Pred0 == ICmpInst::ICMP_EQ && Pred1 == ICmpInst::ICMP_NE)
+    return Cmp1;
+  // (ctpop(X) != C) && (X == 0) --> X == 0 where C > 0
+  if (IsAnd && Pred0 == ICmpInst::ICMP_NE && Pred1 == ICmpInst::ICMP_EQ)
+    return Cmp1;
+
+  return nullptr;
+}
+
 static Value *simplifyAndOfICmps(ICmpInst *Op0, ICmpInst *Op1,
                                  const SimplifyQuery &Q) {
   if (Value *X = simplifyUnsignedRangeCheck(Op0, Op1, /*IsAnd=*/true, Q))
     return X;
   if (Value *X = simplifyUnsignedRangeCheck(Op1, Op0, /*IsAnd=*/true, Q))
     return X;
 
   if (Value *X = simplifyAndOfICmpsWithSameOperands(Op0, Op1))
     return X;
   if (Value *X = simplifyAndOfICmpsWithSameOperands(Op1, Op0))
     return X;
 
   if (Value *X = simplifyAndOrOfICmpsWithConstants(Op0, Op1, true))
     return X;
 
   if (Value *X = simplifyAndOrOfICmpsWithLimitConst(Op0, Op1, true))
     return X;
 
   if (Value *X = simplifyAndOrOfICmpsWithZero(Op0, Op1, true))
     return X;
 
+  if (Value *X = simplifyAndOrOfICmpsWithCtpop(Op0, Op1, true))
+    return X;
+  if (Value *X = simplifyAndOrOfICmpsWithCtpop(Op1, Op0, true))
+    return X;
+
   if (Value *X = simplifyAndOfICmpsWithAdd(Op0, Op1, Q.IIQ))
     return X;
   if (Value *X = simplifyAndOfICmpsWithAdd(Op1, Op0, Q.IIQ))
     return X;
 
   return nullptr;
 }
 
if (Value *X = simplifyAndOrOfICmpsWithConstants(Op0, Op1, false))
     return X;
 
   if (Value *X = simplifyAndOrOfICmpsWithLimitConst(Op0, Op1, false))
     return X;
 
   if (Value *X = simplifyAndOrOfICmpsWithZero(Op0, Op1, false))
     return X;
 
+  if (Value *X = simplifyAndOrOfICmpsWithCtpop(Op0, Op1, false))
+    return X;
+  if (Value *X = simplifyAndOrOfICmpsWithCtpop(Op1, Op0, false))
+    return X;
+
   if (Value *X = simplifyOrOfICmpsWithAdd(Op0, Op1, Q.IIQ))
     return X;
   if (Value *X = simplifyOrOfICmpsWithAdd(Op1, Op0, Q.IIQ))
     return X;
 
   return nullptr;
 }
 

llvm/test/Transforms/InstSimplify/and-or-icmp-ctpop.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;
 ; (ctpop(X) == N) || (X != 0) --> X != 0
 ; where N > 0
 ;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 declare i32 @llvm.ctpop.i32(i32)
 
 define i1 @eq_or_non_0(i32 %x) {
 ; CHECK-LABEL: @eq_or_non_0(
-; CHECK-NEXT:    [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[T0]], 10
-; CHECK-NEXT:    [[NOTZERO:%.*]] = icmp ne i32 [[X]], 0
-; CHECK-NEXT:    [[R:%.*]] = or i1 [[NOTZERO]], [[CMP]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    [[NOTZERO:%.*]] = icmp ne i32 [[X:%.*]], 0
+; CHECK-NEXT:    ret i1 [[NOTZERO]]
 ;
   %t0 = tail call i32 @llvm.ctpop.i32(i32 %x)
   %cmp = icmp eq i32 %t0, 10
   %notzero = icmp ne i32 %x, 0
   %r = or i1 %notzero, %cmp
   ret i1 %r
 }
 
 declare <2 x i32> @llvm.ctpop.v2i32(<2 x i32>)
 
 define <2 x i1> @eq_or_non_0_commute(<2 x i32> %x) {
 ; CHECK-LABEL: @eq_or_non_0_commute(
-; CHECK-NEXT:    [[T0:%.*]] = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <2 x i32> [[T0]], <i32 20, i32 20>
-; CHECK-NEXT:    [[NOTZERO:%.*]] = icmp ne <2 x i32> [[X]], zeroinitializer
-; CHECK-NEXT:    [[R:%.*]] = or <2 x i1> [[CMP]], [[NOTZERO]]
-; CHECK-NEXT:    ret <2 x i1> [[R]]
+; CHECK-NEXT:    [[NOTZERO:%.*]] = icmp ne <2 x i32> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    ret <2 x i1> [[NOTZERO]]
 ;
   %t0 = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> %x)
   %cmp = icmp eq <2 x i32> %t0, <i32 20, i32 20>
   %notzero = icmp ne <2 x i32> %x, <i32 0, i32 0>
   %r = or <2 x i1> %cmp, %notzero
   ret <2 x i1> %r
 }
 
 ; Negative test - wrong predicate
 
 define i1 @eq_or_non_0_wrong_pred1(i32 %x) {
 ; CHECK-LABEL: @eq_or_non_0_wrong_pred1(
 ; CHECK-NEXT:    [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]])

 ;
 ; (ctpop(X) != N) && (X == 0) --> X == 0
 ; where N > 0
 ;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 define i1 @ne_and_is_0(i32 %x) {
 ; CHECK-LABEL: @ne_and_is_0(
-; CHECK-NEXT:    [[T0:%.*]] = tail call i32 @llvm.ctpop.i32(i32 [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[T0]], 10
-; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq i32 [[X]], 0
-; CHECK-NEXT:    [[R:%.*]] = and i1 [[ISZERO]], [[CMP]]
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq i32 [[X:%.*]], 0
+; CHECK-NEXT:    ret i1 [[ISZERO]]
 ;
   %t0 = tail call i32 @llvm.ctpop.i32(i32 %x)
   %cmp = icmp ne i32 %t0, 10
   %iszero = icmp eq i32 %x, 0
   %r = and i1 %iszero, %cmp
   ret i1 %r
 }
 
 define <2 x i1> @ne_and_is_0_commute(<2 x i32> %x) {
 ; CHECK-LABEL: @ne_and_is_0_commute(
-; CHECK-NEXT:    [[T0:%.*]] = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne <2 x i32> [[T0]], <i32 20, i32 20>
-; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq <2 x i32> [[X]], zeroinitializer
-; CHECK-NEXT:    [[R:%.*]] = and <2 x i1> [[CMP]], [[ISZERO]]
-; CHECK-NEXT:    ret <2 x i1> [[R]]
+; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq <2 x i32> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    ret <2 x i1> [[ISZERO]]
 ;
   %t0 = tail call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> %x)
   %cmp = icmp ne <2 x i32> %t0, <i32 20, i32 20>
   %iszero = icmp eq <2 x i32> %x, <i32 0, i32 0>
   %r = and <2 x i1> %cmp, %iszero
   ret <2 x i1> %r
 }