[llvm] [InstCombine] Generalize `icmp (shl nuw C2, Y), C -> icmp Y, C3` (PR #104696)

[Nikita Popov via llvm-commits]

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@@ -90,3 +90,109 @@ define <2 x i1> @icmp_ugt_16x2(<2 x i32>) {
   %d = icmp ugt <2 x i32> %c, <i32 1048575, i32 1048575>
   ret <2 x i1> %d
 }
+
+define i1 @fold_icmp_shl_nuw_c1(i32 %x) {
+; CHECK-LABEL: @fold_icmp_shl_nuw_c1(
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[X:%.*]], 61440
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %lshr = lshr i32 %x, 12
+  %and = and i32 %lshr, 15
+  %shl = shl nuw i32 2, %and
+  %cmp = icmp ult i32 %shl, 4
+  ret i1 %cmp
+}
+
+define i1 @fold_icmp_shl_nuw_c2(i32 %x) {
+; CHECK-LABEL: @fold_icmp_shl_nuw_c2(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[X:%.*]], 2
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %shl = shl nuw i32 16, %x
+  %cmp = icmp ult i32 %shl, 64
+  ret i1 %cmp
+}
+
+define i1 @fold_icmp_shl_nuw_c2_non_pow2(i32 %x) {
+; CHECK-LABEL: @fold_icmp_shl_nuw_c2_non_pow2(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[X:%.*]], 2
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %shl = shl nuw i32 48, %x
+  %cmp = icmp ult i32 %shl, 192
+  ret i1 %cmp
+}
+
+define i1 @fold_icmp_shl_nuw_c2_div_non_pow2(i32 %x) {
+; CHECK-LABEL: @fold_icmp_shl_nuw_c2_div_non_pow2(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[X:%.*]], 5
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %shl = shl nuw i32 2, %x
+  %cmp = icmp ult i32 %shl, 60
+  ret i1 %cmp
+}
+
+define i1 @fold_icmp_shl_nuw_c3(i32 %x) {
+; CHECK-LABEL: @fold_icmp_shl_nuw_c3(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[X:%.*]], 1
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %shl = shl nuw i32 48, %x
+  %cmp = icmp uge i32 %shl, 144
+  ret i1 %cmp
+}
+
+; Negative tests
----------------
nikic wrote:

The first test here is no longer a negative test?

https://github.com/llvm/llvm-project/pull/104696