[llvm] [GlobalIsel] Combine cast of const integer. (PR #96139)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,45 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs -mtriple aarch64-unknown-unknown %s -o - | FileCheck %s
+
+---
+name:            zext_const
+body:             |
+  bb.0:
+    liveins: $w0, $w1
+    ; CHECK-LABEL: name: zext_const
+    ; CHECK: liveins: $w0, $w1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 5
+    ; CHECK-NEXT: $x0 = COPY [[C]](s64)
+    %2:_(s32) = G_CONSTANT i32 5
+    %3:_(s64) = G_ZEXT %2
+    $x0 = COPY %3
+...
+---
+name:            sext_const
+body:             |
+  bb.0:
+    liveins: $q0, $q1
+    ; CHECK-LABEL: name: sext_const
+    ; CHECK: liveins: $q0, $q1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 -5
+    ; CHECK-NEXT: $x0 = COPY [[C]](s64)
+    %2:_(s32) = G_CONSTANT i32 -5
+    %3:_(s64) = G_SEXT %2
+    $x0 = COPY %3
+...
+---
+name:            trunc_const
+body:             |
+  bb.0:
+    liveins: $q0, $q1
+    ; CHECK-LABEL: name: trunc_const
+    ; CHECK: liveins: $q0, $q1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 705032704
+    ; CHECK-NEXT: $w0 = COPY [[C]](s32)
+    %2:_(s64) = G_CONSTANT i64 5000000000
+    %3:_(s32) = G_TRUNC %2
+    $w0 = COPY %3
+
----------------
arsenm wrote:

Check vector cases 

https://github.com/llvm/llvm-project/pull/96139