[llvm] [InstCombine] simplify `icmp pred x, ~x` (PR #73990)

[via llvm-commits]

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@@ -5,6 +5,521 @@ declare void @llvm.assume(i1)
 declare void @barrier()
 declare void @use.i8(i8)
 
+; X op ~X tests. op signed
+; X s< ~X   -->      X s< 0
+define i1 @src_slt(i8 %x) {
+; CHECK-LABEL: @src_slt(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i8 [[X:%.*]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %not = xor i8 %x, -1
+  %cmp = icmp slt i8 %x, %not
+  ret i1 %cmp
+}
+define i1 @src_slt_i128(i128 %x) {
+; CHECK-LABEL: @src_slt_i128(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i128 [[X:%.*]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %not = xor i128 %x, -1
+  %cmp = icmp slt i128 %x, %not
+  ret i1 %cmp
+}
+; X s> ~X   -->     X s> -1
+define i1 @src_sgt(i8 %x) {
+; CHECK-LABEL: @src_sgt(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], -1
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %not = xor i8 %x, -1
+  %cmp = icmp sgt i8 %x, %not
+  ret i1 %cmp
+}
+define i1 @src_sgt_i128(i128 %x) {
+; CHECK-LABEL: @src_sgt_i128(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i128 [[X:%.*]], -1
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %not = xor i128 %x, -1
+  %cmp = icmp sgt i128 %x, %not
+  ret i1 %cmp
+}
+; X s<= ~X   -->      X s< 0
+define i1 @src_sle(i8 %x) {
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ParkHanbum wrote:

@nikic maybe this problem solved after implemented code moved to `foidIcmpXorXX`. how do you think?

https://github.com/llvm/llvm-project/pull/73990