[llvm] [SCCP] Simplify [us]cmp(X, Y) into X - Y (PR #144717)

[Yingwei Zheng via llvm-commits]

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@@ -0,0 +1,78 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=sccp -S < %s | FileCheck %s
+
+define i32 @scmp_to_sub(i32 range(i32 -1, 2) %a) {
+; CHECK-LABEL: define i32 @scmp_to_sub(
+; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
+; CHECK-NEXT:    [[SCMP:%.*]] = sub nsw i32 [[A]], 0
+; CHECK-NEXT:    ret i32 [[SCMP]]
+;
+  %scmp = call i32 @llvm.scmp(i32 %a, i32 0)
+  ret i32 %scmp
+}
+
+define i32 @scmp_zext_to_sub(i1 %a, i1 %b) {
+; CHECK-LABEL: define i32 @scmp_zext_to_sub(
+; CHECK-SAME: i1 [[A:%.*]], i1 [[B:%.*]]) {
+; CHECK-NEXT:    [[ZEXT_A:%.*]] = zext i1 [[A]] to i32
+; CHECK-NEXT:    [[ZEXT_B:%.*]] = zext i1 [[B]] to i32
+; CHECK-NEXT:    [[SCMP:%.*]] = sub nsw i32 [[ZEXT_A]], [[ZEXT_B]]
+; CHECK-NEXT:    ret i32 [[SCMP]]
+;
+  %zext_a = zext i1 %a to i32
+  %zext_b = zext i1 %b to i32
+  %scmp = call i32 @llvm.scmp(i32 %zext_a, i32 %zext_b)
+  ret i32 %scmp
+}
+
+define i8 @scmp_to_sub_trunc(i32 range(i32 -1, 2) %a) {
+; CHECK-LABEL: define i8 @scmp_to_sub_trunc(
+; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
+; CHECK-NEXT:    [[SCMP1:%.*]] = sub nsw i32 [[A]], 0
+; CHECK-NEXT:    [[SCMP:%.*]] = trunc i32 [[SCMP1]] to i8
+; CHECK-NEXT:    ret i8 [[SCMP]]
+;
+  %scmp = call i8 @llvm.scmp(i32 %a, i32 0)
+  ret i8 %scmp
+}
+
+define i64 @scmp_to_sub_sext(i32 range(i32 -1, 2) %a) {
+; CHECK-LABEL: define i64 @scmp_to_sub_sext(
+; CHECK-SAME: i32 range(i32 -1, 2) [[A:%.*]]) {
+; CHECK-NEXT:    [[SCMP1:%.*]] = sub nsw i32 [[A]], 0
+; CHECK-NEXT:    [[SCMP:%.*]] = sext i32 [[SCMP1]] to i64
+; CHECK-NEXT:    ret i64 [[SCMP]]
+;
+  %scmp = call i64 @llvm.scmp(i32 %a, i32 0)
+  ret i64 %scmp
+}
+
+define i32 @scmp_to_sub_small_range(i32 range(i32 -1, 1) %a) {
+; CHECK-LABEL: define i32 @scmp_to_sub_small_range(
+; CHECK-SAME: i32 range(i32 -1, 1) [[A:%.*]]) {
+; CHECK-NEXT:    [[SCMP:%.*]] = sub nsw i32 [[A]], 0
+; CHECK-NEXT:    ret i32 [[SCMP]]
+;
+  %scmp = call i32 @llvm.scmp(i32 %a, i32 0)
+  ret i32 %scmp
+}
+
+define i32 @ucmp_to_sub(i32 range(i32 0, 3) %a) {
+; CHECK-LABEL: define i32 @ucmp_to_sub(
+; CHECK-SAME: i32 range(i32 0, 3) [[A:%.*]]) {
+; CHECK-NEXT:    [[SCMP:%.*]] = sub nsw i32 [[A]], 1
+; CHECK-NEXT:    ret i32 [[SCMP]]
+;
+  %scmp = call i32 @llvm.scmp(i32 %a, i32 1)
+  ret i32 %scmp
+}
+
+define i32 @scmp_to_sub_large_range(i32 range(i32 -1, 3) %a) {
+; CHECK-LABEL: define i32 @scmp_to_sub_large_range(
+; CHECK-SAME: i32 range(i32 -1, 3) [[A:%.*]]) {
+; CHECK-NEXT:    [[SCMP:%.*]] = call i32 @llvm.scmp.i32.i32(i32 [[A]], i32 0)
+; CHECK-NEXT:    ret i32 [[SCMP]]
+;
+  %scmp = call i32 @llvm.scmp(i32 %a, i32 0)
+  ret i32 %scmp
+}
----------------
dtcxzyw wrote:

> That's why the precondition is expressed in such a roundabout way, right?

Yeah. I don't have a better idea to weaken the precondition (see the test `ucmp_to_sub_small_range`).

https://github.com/llvm/llvm-project/pull/144717