Add test to check we can instcombine after reassociate. NFC.

[rampitec]

Summary

The pattern became optimized after b92412fb286b.

[spatel]

LGTM - feel free to add tests without pre-commit review.
I would add the 'or' variant of this pattern too for completeness:

define i32 @not_reassociate_or_or_not(i32 %a, i32 %b, i32 %c, i32 %d) {
  %notb = xor i32 %b, -1
  %notc = xor i32 %c, -1
  %b1 = or i32 %a, %notb
  %b2 = or i32 %b1, %d
  %b3 = or i32 %b2, %notc
  ret i32 %b3
}

llvm/test/Transforms/PhaseOrdering/reassociate-instcombine.ll

4

siplify -> "allow Demorgan logic fold" ?

[rampitec]

Added second test.

llvm/test/Transforms/PhaseOrdering/reassociate-instcombine.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -O1 -S < %s | FileCheck %s
+
+; Make sure we reassociate and1 with and2 before instcombine to siplify
+; (a & ~b) & ~c --> a & ~(b | c)
+define i4 @not_reassociate_and_and_not(i4 %a, i4 %b, i4 %c, i4 %d) {
+; CHECK-LABEL: @not_reassociate_and_and_not(
+; CHECK-NEXT:    [[TMP1:%.*]] = or i4 [[B:%.*]], [[C:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = xor i4 [[TMP1]], -1
+; CHECK-NEXT:    [[AND2:%.*]] = and i4 [[TMP2]], [[A:%.*]]
+; CHECK-NEXT:    [[AND3:%.*]] = and i4 [[AND2]], [[D:%.*]]
+; CHECK-NEXT:    ret i4 [[AND3]]
+;
+  %notb = xor i4 %b, -1
+  %notc = xor i4 %c, -1
+  %and1 = and i4 %a, %notb
+  %and2 = and i4 %and1, %d
+  %and3 = and i4 %and2, %notc
+  ret i4 %and3
+}