[llvm] [CodeGen] Add preliminary plumbing for `samesign` flag (PR #112354)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,38 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -march=x86-64 -run-pass none -verify-machineinstrs -o - %s | FileCheck %s
+
+--- |
+
+  define i1 @icmp_samesign(i32 %a, i32 %b) {
+  entry:
+    %res = icmp samesign ult i32 %a, %b
+    ret i1 %res
+  }
+
+...
+---
+name:            icmp_samesign
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gr32 }
+  - { id: 1, class: gr32 }
+liveins:
+  - { reg: '$edi', virtual-reg: '%0' }
+  - { reg: '$esi', virtual-reg: '%1' }
+body: |
+  bb.0.entry:
+    liveins: $edi, $esi
+    ; CHECK-LABEL: name: icmp_samesign
+    ; CHECK: liveins: $edi, $esi
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:gr32 = COPY $esi
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:gr32 = COPY $edi
+    ; CHECK-NEXT: samesign CMP32rr killed [[COPY1]], killed [[COPY]], implicit-def $eflags
+    ; CHECK-NEXT: $al = SETCCr 2, implicit killed $eflags
+    ; CHECK-NEXT: RET 0, $al
+    %1 = COPY $esi
+    %0 = COPY $edi
+    samesign CMP32rr killed %0, killed %1, implicit-def $eflags
+    $al = SETCCr 2, implicit killed $eflags
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arsenm wrote:

Would be more sensible to have this on a G_MIR instruction as a sample 

https://github.com/llvm/llvm-project/pull/112354