[llvm] [InstCombine] Fold umax(nuw_mul(x, C0), x + 1) into (x == 0 ? 1 : nuw_mul(x, C0)) (PR #123468)

[Nikita Popov via llvm-commits]

================
@@ -0,0 +1,358 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+; When C0 is neither 0 nor 1:
+;   umax(nuw_mul(x, C0), x + 1) is optimized to:
+;   x == 0 ? 1 : nuw_mul(x, C0)
+; When C0 is not 0:
+;   umax(nuw_shl(x, C0), x + 1) is optimized to:
+;   x == 0 ? 1 : nuw_shl(x, C0)
+
+; Positive Test Cases for `shl`
+
+define i64 @test_shl_by_2(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_by_2(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[TMP2:%.*]] = shl nuw i64 [[X]], 2
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[X]], 0
+; CHECK-NEXT:    [[MAX:%.*]] = select i1 [[TMP1]], i64 1, i64 [[TMP2]]
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw i64 %x, 2
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+define i64 @test_shl_by_5(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_by_5(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[TMP2:%.*]] = shl nuw i64 [[X]], 5
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[X]], 0
+; CHECK-NEXT:    [[MAX:%.*]] = select i1 [[TMP1]], i64 1, i64 [[TMP2]]
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw i64 %x, 5
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+define i64 @test_shl_with_nsw(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_with_nsw(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw nsw i64 [[X]], 2
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[X]], 0
+; CHECK-NEXT:    [[MAX:%.*]] = select i1 [[TMP1]], i64 1, i64 [[SHL]]
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw nsw i64 %x, 2
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+; Commuted Test Cases for `shl`
+
+define i64 @test_shl_umax_commuted(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_umax_commuted(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i64 [[X]], 2
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[X]], 0
+; CHECK-NEXT:    [[MAX:%.*]] = select i1 [[TMP1]], i64 1, i64 [[SHL]]
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw i64 %x, 2
+  %max = call i64 @llvm.umax.i64(i64 %x1, i64 %shl)
+  ret i64 %max
+}
+
+; Negative Test Cases for `shl`
+
+define i64 @test_shl_by_zero(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_by_zero(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[X1:%.*]] = add i64 [[X]], 1
+; CHECK-NEXT:    [[MAX:%.*]] = call i64 @llvm.umax.i64(i64 [[X]], i64 [[X1]])
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw i64 %x, 0
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+define i64 @test_shl_add_by_2(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_add_by_2(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[X1:%.*]] = add i64 [[X]], 2
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i64 [[X]], 2
+; CHECK-NEXT:    [[MAX:%.*]] = call i64 @llvm.umax.i64(i64 [[SHL]], i64 [[X1]])
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 2
+  %shl = shl nuw i64 %x, 2
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+define i64 @test_shl_without_nuw(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_without_nuw(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[X1:%.*]] = add i64 [[X]], 1
+; CHECK-NEXT:    [[SHL:%.*]] = shl i64 [[X]], 2
+; CHECK-NEXT:    [[MAX:%.*]] = call i64 @llvm.umax.i64(i64 [[SHL]], i64 [[X1]])
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl i64 %x, 2
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+define i64 @test_shl_umin(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_umin(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[X1:%.*]] = add i64 [[X]], 1
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i64 [[X]], 2
+; CHECK-NEXT:    [[MAX:%.*]] = call i64 @llvm.umin.i64(i64 [[SHL]], i64 [[X1]])
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw i64 %x, 2
+  %max = call i64 @llvm.umin.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+; Multi-use Test Cases for `shl`
+declare void @use(i64)
+
+define i64 @test_shl_multi_use_add(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_multi_use_add(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[X1:%.*]] = add i64 [[X]], 1
+; CHECK-NEXT:    call void @use(i64 [[X1]])
+; CHECK-NEXT:    [[TMP2:%.*]] = shl nuw i64 [[X]], 3
+; CHECK-NEXT:    [[MAX:%.*]] = call i64 @llvm.umax.i64(i64 [[TMP2]], i64 [[X1]])
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  call void @use(i64 %x1)
+  %shl = shl nuw i64 %x, 3
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+define i64 @test_shl_multi_use_shl(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_multi_use_shl(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[SHL:%.*]] = shl nuw i64 [[X]], 2
+; CHECK-NEXT:    call void @use(i64 [[SHL]])
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[X]], 0
+; CHECK-NEXT:    [[MAX:%.*]] = select i1 [[TMP1]], i64 1, i64 [[SHL]]
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw i64 %x, 2
+  call void @use(i64 %shl)
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  ret i64 %max
+}
+
+define i64 @test_shl_multi_use_max(i64 %x) {
+; CHECK-LABEL: define i64 @test_shl_multi_use_max(
+; CHECK-SAME: i64 [[X:%.*]]) {
+; CHECK-NEXT:    [[TMP2:%.*]] = shl nuw i64 [[X]], 3
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[X]], 0
+; CHECK-NEXT:    [[MAX:%.*]] = select i1 [[TMP1]], i64 1, i64 [[TMP2]]
+; CHECK-NEXT:    call void @use(i64 [[MAX]])
+; CHECK-NEXT:    ret i64 [[MAX]]
+;
+  %x1 = add i64 %x, 1
+  %shl = shl nuw i64 %x, 3
+  %max = call i64 @llvm.umax.i64(i64 %shl, i64 %x1)
+  call void @use(i64 %max)
----------------
nikic wrote:

No need to test multi-use on the root instruction.

https://github.com/llvm/llvm-project/pull/123468