Use unsigned arithmetic builtins for UInt(N) operations (#4740)

We were mistakenly using the signed builtins, which produce the same
lowering for add/multiply right now, but don't for division and modulus.

When manually flipping SignedOverflowIsUB on, the signed version of add
gains the nsw (no signed wrap) flag, while the unsigned version
(correctly after this change) does not:
```
// CHECK:STDOUT: define i32 @_Cadd_i32.Main(i32 %a, i32 %b) !dbg !4 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT:   %int.sadd = add nsw i32 %a, %b, !dbg !7
// CHECK:STDOUT:   ret i32 %int.sadd, !dbg !8
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: define i32 @_Cadd_u32.Main(i32 %a, i32 %b) !dbg !9 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT:   %int.uadd = add i32 %a, %b, !dbg !10
// CHECK:STDOUT:   ret i32 %int.uadd, !dbg !11
// CHECK:STDOUT: }
```

core/prelude/types/uint.carbon

@@ -50,19 +50,19 @@ impl forall [N:! IntLiteral()] UInt(N) as Ordered {
 // Arithmetic.
 
 impl forall [N:! IntLiteral()] UInt(N) as Add {
-  fn Op[self: Self](other: Self) -> Self = "int.sadd";
+  fn Op[self: Self](other: Self) -> Self = "int.uadd";
 }
 
 impl forall [N:! IntLiteral()] UInt(N) as Div {
-  fn Op[self: Self](other: Self) -> Self = "int.sdiv";
+  fn Op[self: Self](other: Self) -> Self = "int.udiv";
 }
 
 impl forall [N:! IntLiteral()] UInt(N) as Mod {
-  fn Op[self: Self](other: Self) -> Self = "int.smod";
+  fn Op[self: Self](other: Self) -> Self = "int.umod";
 }
 
 impl forall [N:! IntLiteral()] UInt(N) as Mul {
-  fn Op[self: Self](other: Self) -> Self = "int.smul";
+  fn Op[self: Self](other: Self) -> Self = "int.umul";
 }
 
 impl forall [N:! IntLiteral()] UInt(N) as Negate {
@@ -70,7 +70,7 @@ impl forall [N:! IntLiteral()] UInt(N) as Negate {
 }
 
 impl forall [N:! IntLiteral()] UInt(N) as Sub {
-  fn Op[self: Self](other: Self) -> Self = "int.ssub";
+  fn Op[self: Self](other: Self) -> Self = "int.usub";
 }
 
 // Bitwise operators.

toolchain/lower/testdata/operators/arithmetic.carbon

@@ -0,0 +1,174 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/operators/arithmetic.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/operators/arithmetic.carbon
+
+// Test each of the arithmetic operations, signed and unsigned values may lower
+// differently.
+
+fn add_i32(a: i32, b: i32) -> i32 { return a + b; }
+fn add_u32(a: u32, b: u32) -> u32 { return a + b; }
+
+fn div_i32(a: i32, b: i32) -> i32 { return a / b; }
+fn div_u32(a: u32, b: u32) -> u32 { return a / b; }
+
+fn mod_i32(a: i32, b: i32) -> i32 { return a % b; }
+fn mod_u32(a: u32, b: u32) -> u32 { return a % b; }
+
+fn mul_i32(a: i32, b: i32) -> i32 { return a * b; }
+fn mul_u32(a: u32, b: u32) -> u32 { return a * b; }
+
+fn neg_i32(a: i32) -> i32 { return -a; }
+fn neg_u32(a: u32) -> u32 { return -a; }
+
+fn sub_i32(a: i32, b: i32) -> i32 { return a - b; }
+fn sub_u32(a: u32, b: u32) -> u32 { return a - b; }
+
+// One test for non-32 bit, verify the size is correct.
+
+fn div_i16(a: i16, b: i16) -> i16 { return a / b; }
+fn div_u16(a: u16, b: u16) -> u16 { return a / b; }
+
+// CHECK:STDOUT: ; ModuleID = 'arithmetic.carbon'
+// CHECK:STDOUT: source_filename = "arithmetic.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cadd_i32.Main(i32 %a, i32 %b) !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.sadd = add i32 %a, %b, !dbg !7
+// CHECK:STDOUT:   ret i32 %int.sadd, !dbg !8
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cadd_u32.Main(i32 %a, i32 %b) !dbg !9 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.uadd = add i32 %a, %b, !dbg !10
+// CHECK:STDOUT:   ret i32 %int.uadd, !dbg !11
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cdiv_i32.Main(i32 %a, i32 %b) !dbg !12 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.sdiv = sdiv i32 %a, %b, !dbg !13
+// CHECK:STDOUT:   ret i32 %int.sdiv, !dbg !14
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cdiv_u32.Main(i32 %a, i32 %b) !dbg !15 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.udiv = udiv i32 %a, %b, !dbg !16
+// CHECK:STDOUT:   ret i32 %int.udiv, !dbg !17
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cmod_i32.Main(i32 %a, i32 %b) !dbg !18 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.smod = srem i32 %a, %b, !dbg !19
+// CHECK:STDOUT:   ret i32 %int.smod, !dbg !20
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cmod_u32.Main(i32 %a, i32 %b) !dbg !21 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.umod = urem i32 %a, %b, !dbg !22
+// CHECK:STDOUT:   ret i32 %int.umod, !dbg !23
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cmul_i32.Main(i32 %a, i32 %b) !dbg !24 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.smul = mul i32 %a, %b, !dbg !25
+// CHECK:STDOUT:   ret i32 %int.smul, !dbg !26
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cmul_u32.Main(i32 %a, i32 %b) !dbg !27 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.umul = mul i32 %a, %b, !dbg !28
+// CHECK:STDOUT:   ret i32 %int.umul, !dbg !29
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cneg_i32.Main(i32 %a) !dbg !30 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.snegate = sub i32 0, %a, !dbg !31
+// CHECK:STDOUT:   ret i32 %int.snegate, !dbg !32
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Cneg_u32.Main(i32 %a) !dbg !33 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.snegate = sub i32 0, %a, !dbg !34
+// CHECK:STDOUT:   ret i32 %int.snegate, !dbg !35
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Csub_i32.Main(i32 %a, i32 %b) !dbg !36 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.ssub = sub i32 %a, %b, !dbg !37
+// CHECK:STDOUT:   ret i32 %int.ssub, !dbg !38
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i32 @_Csub_u32.Main(i32 %a, i32 %b) !dbg !39 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.usub = sub i32 %a, %b, !dbg !40
+// CHECK:STDOUT:   ret i32 %int.usub, !dbg !41
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i16 @_Cdiv_i16.Main(i16 %a, i16 %b) !dbg !42 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.sdiv = sdiv i16 %a, %b, !dbg !43
+// CHECK:STDOUT:   ret i16 %int.sdiv, !dbg !44
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: define i16 @_Cdiv_u16.Main(i16 %a, i16 %b) !dbg !45 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %int.udiv = udiv i16 %a, %b, !dbg !46
+// CHECK:STDOUT:   ret i16 %int.udiv, !dbg !47
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "arithmetic.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "add_i32", linkageName: "_Cadd_i32.Main", scope: null, file: !3, line: 14, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{}
+// CHECK:STDOUT: !7 = !DILocation(line: 14, column: 44, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 14, column: 37, scope: !4)
+// CHECK:STDOUT: !9 = distinct !DISubprogram(name: "add_u32", linkageName: "_Cadd_u32.Main", scope: null, file: !3, line: 15, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !10 = !DILocation(line: 15, column: 44, scope: !9)
+// CHECK:STDOUT: !11 = !DILocation(line: 15, column: 37, scope: !9)
+// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "div_i32", linkageName: "_Cdiv_i32.Main", scope: null, file: !3, line: 17, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !13 = !DILocation(line: 17, column: 44, scope: !12)
+// CHECK:STDOUT: !14 = !DILocation(line: 17, column: 37, scope: !12)
+// CHECK:STDOUT: !15 = distinct !DISubprogram(name: "div_u32", linkageName: "_Cdiv_u32.Main", scope: null, file: !3, line: 18, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !16 = !DILocation(line: 18, column: 44, scope: !15)
+// CHECK:STDOUT: !17 = !DILocation(line: 18, column: 37, scope: !15)
+// CHECK:STDOUT: !18 = distinct !DISubprogram(name: "mod_i32", linkageName: "_Cmod_i32.Main", scope: null, file: !3, line: 20, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !19 = !DILocation(line: 20, column: 44, scope: !18)
+// CHECK:STDOUT: !20 = !DILocation(line: 20, column: 37, scope: !18)
+// CHECK:STDOUT: !21 = distinct !DISubprogram(name: "mod_u32", linkageName: "_Cmod_u32.Main", scope: null, file: !3, line: 21, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !22 = !DILocation(line: 21, column: 44, scope: !21)
+// CHECK:STDOUT: !23 = !DILocation(line: 21, column: 37, scope: !21)
+// CHECK:STDOUT: !24 = distinct !DISubprogram(name: "mul_i32", linkageName: "_Cmul_i32.Main", scope: null, file: !3, line: 23, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !25 = !DILocation(line: 23, column: 44, scope: !24)
+// CHECK:STDOUT: !26 = !DILocation(line: 23, column: 37, scope: !24)
+// CHECK:STDOUT: !27 = distinct !DISubprogram(name: "mul_u32", linkageName: "_Cmul_u32.Main", scope: null, file: !3, line: 24, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !28 = !DILocation(line: 24, column: 44, scope: !27)
+// CHECK:STDOUT: !29 = !DILocation(line: 24, column: 37, scope: !27)
+// CHECK:STDOUT: !30 = distinct !DISubprogram(name: "neg_i32", linkageName: "_Cneg_i32.Main", scope: null, file: !3, line: 26, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !31 = !DILocation(line: 26, column: 36, scope: !30)
+// CHECK:STDOUT: !32 = !DILocation(line: 26, column: 29, scope: !30)
+// CHECK:STDOUT: !33 = distinct !DISubprogram(name: "neg_u32", linkageName: "_Cneg_u32.Main", scope: null, file: !3, line: 27, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !34 = !DILocation(line: 27, column: 36, scope: !33)
+// CHECK:STDOUT: !35 = !DILocation(line: 27, column: 29, scope: !33)
+// CHECK:STDOUT: !36 = distinct !DISubprogram(name: "sub_i32", linkageName: "_Csub_i32.Main", scope: null, file: !3, line: 29, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !37 = !DILocation(line: 29, column: 44, scope: !36)
+// CHECK:STDOUT: !38 = !DILocation(line: 29, column: 37, scope: !36)
+// CHECK:STDOUT: !39 = distinct !DISubprogram(name: "sub_u32", linkageName: "_Csub_u32.Main", scope: null, file: !3, line: 30, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !40 = !DILocation(line: 30, column: 44, scope: !39)
+// CHECK:STDOUT: !41 = !DILocation(line: 30, column: 37, scope: !39)
+// CHECK:STDOUT: !42 = distinct !DISubprogram(name: "div_i16", linkageName: "_Cdiv_i16.Main", scope: null, file: !3, line: 34, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !43 = !DILocation(line: 34, column: 44, scope: !42)
+// CHECK:STDOUT: !44 = !DILocation(line: 34, column: 37, scope: !42)
+// CHECK:STDOUT: !45 = distinct !DISubprogram(name: "div_u16", linkageName: "_Cdiv_u16.Main", scope: null, file: !3, line: 35, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !46 = !DILocation(line: 35, column: 44, scope: !45)
+// CHECK:STDOUT: !47 = !DILocation(line: 35, column: 37, scope: !45)