[InstCombine] reduce icmp_eq0-of-and-of-select-of-constants

This is the most basic patch to handle fixing issue #57666.

D133919 proposes to handle much more than this in a single patch,
but I've used 10 regression tests just to make sure this part is
doing what I expected and nothing more, and it already shows even
more potential TODO items.

The more general proofs from D133919 are correct, but I want to
enable this in smaller steps to reduce risk:
https://alive2.llvm.org/ce/z/RrVEyX

Differential Revision: https://reviews.llvm.org/D142847

Author: rotateright

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -1888,6 +1888,25 @@ Instruction *InstCombinerImpl::foldICmpAndConstant(ICmpInst &Cmp,
     return new ICmpInst(NewPred, X, SubOne(cast<Constant>(Cmp.getOperand(1))));
   }
 
+  // If we are testing the intersection of 2 select-of-nonzero-constants with no
+  // common bits set, it's the same as checking if exactly one select condition
+  // is set:
+  // ((A ? TC : FC) & (B ? TC : FC)) == 0 --> xor A, B
+  // TODO: Generalize for non-constant values.
+  // TODO: Invert with a "ne" predicate.
+  // TODO: Handle signed/unsigned predicates.
+  // TODO: Handle other bitwise logic connectors.
+  // TODO: Extend to handle a non-zero compare constant.
+  if (Pred == CmpInst::ICMP_EQ && C.isZero()) {
+    Value *A, *B;
+    const APInt *TC, *FC;
+    if (match(X, m_Select(m_Value(A), m_APInt(TC), m_APInt(FC))) &&
+        match(Y,
+              m_Select(m_Value(B), m_SpecificInt(*TC), m_SpecificInt(*FC))) &&
+        !TC->isZero() && !FC->isZero() && !TC->intersects(*FC))
+      return BinaryOperator::CreateXor(A, B);
+  }
+
   // ((zext i1 X) & Y) == 0 --> !((trunc Y) & X)
   // ((zext i1 X) & Y) != 0 -->  ((trunc Y) & X)
   // ((zext i1 X) & Y) == 1 -->  ((trunc Y) & X)

llvm/test/Transforms/InstCombine/icmp-select.ll

@@ -262,10 +262,7 @@ define i1 @umin_seq_comparison(i8 %x, i8 %y) {
 
 define i1 @select_constants_and_icmp_eq0(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0(
-; CHECK-NEXT:    [[S1:%.*]] = select i1 [[X:%.*]], i8 2, i8 1
-; CHECK-NEXT:    [[S2:%.*]] = select i1 [[Y:%.*]], i8 2, i8 1
-; CHECK-NEXT:    [[AND:%.*]] = and i8 [[S1]], [[S2]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[AND]], 0
+; CHECK-NEXT:    [[CMP:%.*]] = xor i1 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %s1 = select i1 %x, i8 2, i8 1
@@ -275,6 +272,8 @@ define i1 @select_constants_and_icmp_eq0(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; extra uses on all intermediates are ok
+
 define i1 @select_constants_and_icmp_eq0_uses(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0_uses(
 ; CHECK-NEXT:    [[S1:%.*]] = select i1 [[X:%.*]], i8 2, i8 1
@@ -283,7 +282,7 @@ define i1 @select_constants_and_icmp_eq0_uses(i1 %x, i1 %y) {
 ; CHECK-NEXT:    call void @use(i8 [[S2]])
 ; CHECK-NEXT:    [[AND:%.*]] = and i8 [[S1]], [[S2]]
 ; CHECK-NEXT:    call void @use(i8 [[AND]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[AND]], 0
+; CHECK-NEXT:    [[CMP:%.*]] = xor i1 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %s1 = select i1 %x, i8 2, i8 1
@@ -296,12 +295,11 @@ define i1 @select_constants_and_icmp_eq0_uses(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; vector splat constants are ok
+
 define <2 x i1> @select_constants_and_icmp_eq0_vec_splat(<2 x i1> %x, <2 x i1> %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0_vec_splat(
-; CHECK-NEXT:    [[S1:%.*]] = select <2 x i1> [[X:%.*]], <2 x i9> <i9 3, i9 3>, <2 x i9> <i9 48, i9 48>
-; CHECK-NEXT:    [[S2:%.*]] = select <2 x i1> [[Y:%.*]], <2 x i9> <i9 3, i9 3>, <2 x i9> <i9 48, i9 48>
-; CHECK-NEXT:    [[AND:%.*]] = and <2 x i9> [[S1]], [[S2]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <2 x i9> [[AND]], zeroinitializer
+; CHECK-NEXT:    [[CMP:%.*]] = xor <2 x i1> [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret <2 x i1> [[CMP]]
 ;
   %s1 = select <2 x i1> %x, <2 x i9> <i9 3, i9 3>, <2 x i9> <i9 48, i9 48>
@@ -311,6 +309,8 @@ define <2 x i1> @select_constants_and_icmp_eq0_vec_splat(<2 x i1> %x, <2 x i1> %
   ret <2 x i1> %cmp
 }
 
+; common bit set - simplified via known bits
+
 define i1 @select_constants_and_icmp_eq0_common_bit(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0_common_bit(
 ; CHECK-NEXT:    ret i1 false
@@ -322,6 +322,8 @@ define i1 @select_constants_and_icmp_eq0_common_bit(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; negative test - need matching constants
+
 define i1 @select_constants_and_icmp_eq0_no_common_op1(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0_no_common_op1(
 ; CHECK-NEXT:    [[S1:%.*]] = select i1 [[X:%.*]], i8 16, i8 3
@@ -337,6 +339,8 @@ define i1 @select_constants_and_icmp_eq0_no_common_op1(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; negative test - need matching constants
+
 define i1 @select_constants_and_icmp_eq0_no_common_op2(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0_no_common_op2(
 ; CHECK-NEXT:    [[S1:%.*]] = select i1 [[X:%.*]], i8 16, i8 3
@@ -352,6 +356,8 @@ define i1 @select_constants_and_icmp_eq0_no_common_op2(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; reduces via FoldOpInstSelect, but this could be a simple 'or'
+
 define i1 @select_constants_and_icmp_eq0_zero_tval(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0_zero_tval(
 ; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[X:%.*]], i1 true, i1 [[Y:%.*]]
@@ -364,6 +370,8 @@ define i1 @select_constants_and_icmp_eq0_zero_tval(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; reduces via FoldOpInstSelect, but this could be a simple 'not-of-and'
+
 define i1 @select_constants_and_icmp_eq0_zero_fval(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq0_zero_fval(
 ; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[X:%.*]], i1 [[Y:%.*]], i1 false
@@ -377,6 +385,8 @@ define i1 @select_constants_and_icmp_eq0_zero_fval(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; TODO: x & y
+
 define i1 @select_constants_and_icmp_eq_tval(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq_tval(
 ; CHECK-NEXT:    [[S1:%.*]] = select i1 [[X:%.*]], i8 6, i8 1
@@ -392,6 +402,8 @@ define i1 @select_constants_and_icmp_eq_tval(i1 %x, i1 %y) {
   ret i1 %cmp
 }
 
+; TODO: ~(x | y)
+
 define i1 @select_constants_and_icmp_eq_fval(i1 %x, i1 %y) {
 ; CHECK-LABEL: @select_constants_and_icmp_eq_fval(
 ; CHECK-NEXT:    [[S1:%.*]] = select i1 [[X:%.*]], i8 12, i8 3