[InstCombine] isFreeToInvert(): constant expressions aren't free to invert (PR50370)

This fixes https://bugs.llvm.org/show_bug.cgi?id=50370,
which reports a yet another endless combine loop,
this one regressed from 554b1bc,
which fixed yet another endless combine loop (PR50308)

This code had fallen into the very typical pitfall of forgetting
that constant expressions exist, and they aren't free to invert,
because the `not` won't be absorbed by the "constant",
but will remain a (constant) expression...

(cherry-picked from e35a9ec)

Author: LebedevRI

llvm/include/llvm/Transforms/InstCombine/InstCombiner.h

@@ -249,8 +249,8 @@ class LLVM_LIBRARY_VISIBILITY InstCombiner {
     if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
       if (BO->getOpcode() == Instruction::Add ||
           BO->getOpcode() == Instruction::Sub)
-        if (isa<Constant>(BO->getOperand(0)) ||
-            isa<Constant>(BO->getOperand(1)))
+        if (match(BO, PatternMatch::m_c_BinOp(PatternMatch::m_Value(),
+                                              PatternMatch::m_ImmConstant())))
           return WillInvertAllUses;
 
     // Selects with invertible operands are freely invertible

llvm/test/Transforms/InstCombine/not-add.ll

@@ -165,3 +165,35 @@ cond.end:
   %sub = sub nsw i32 %v3, %cond
   ret i32 %sub
 }
+
+@g = extern_weak global i32
+define void @pr50370(i32 %x) {
+; CHECK-LABEL: @pr50370(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[X:%.*]], 1
+; CHECK-NEXT:    [[B15:%.*]] = srem i32 ashr (i32 65536, i32 or (i32 zext (i1 icmp eq (i32* @g, i32* null) to i32), i32 65537)), [[XOR]]
+; CHECK-NEXT:    [[B22:%.*]] = add i32 [[B15]], sdiv (i32 or (i32 zext (i1 icmp eq (i32* @g, i32* null) to i32), i32 65537), i32 2147483647)
+; CHECK-NEXT:    [[B14:%.*]] = srem i32 ashr (i32 65536, i32 or (i32 zext (i1 icmp eq (i32* @g, i32* null) to i32), i32 65537)), [[B22]]
+; CHECK-NEXT:    [[B12:%.*]] = add nuw i32 [[B15]], ashr (i32 65536, i32 or (i32 zext (i1 icmp eq (i32* @g, i32* null) to i32), i32 65537))
+; CHECK-NEXT:    [[B8:%.*]] = shl i32 sdiv (i32 or (i32 zext (i1 icmp eq (i32* @g, i32* null) to i32), i32 65537), i32 2147483647), [[B14]]
+; CHECK-NEXT:    [[B2:%.*]] = xor i32 [[B12]], [[B8]]
+; CHECK-NEXT:    [[B:%.*]] = xor i32 [[B2]], -1
+; CHECK-NEXT:    store i32 [[B]], i32* undef, align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  %xor = xor i32 %x, 1
+  %or4 = or i32 or (i32 zext (i1 icmp eq (i32* @g, i32* null) to i32), i32 1), 65536
+  %B6 = ashr i32 65536, %or4
+  %B15 = srem i32 %B6, %xor
+  %B20 = sdiv i32 %or4, 2147483647
+  %B22 = add i32 %B15, %B20
+  %B14 = srem i32 %B6, %B22
+  %B12 = add i32 %B15, %B6
+  %B8 = shl i32 %B20, %B14
+  %B2 = xor i32 %B12, %B8
+  %B3 = or i32 %B12, undef
+  %B = xor i32 %B2, %B3
+  store i32 %B, i32* undef, align 4
+  ret void
+}