[llvm] [llvm][X86] Fix merging of large sp updates (PR #125007)

[via llvm-commits]

================
@@ -0,0 +1,25 @@
+; RUN: llc < %s -O3 -mtriple=x86_64-linux-unknown -verify-machineinstrs -o %t.s
+; RUN: FileCheck --input-file=%t.s %s
+
+; Check that the stack update after calling bar gets merged into the second add
+; and not the first which is already at the chunk size limit (0x7FFFFFFF).
+
+define void @foo(ptr %rhs) {
+; CHECK-LABEL: foo
+entry:
+  %lhs = alloca [5 x [5 x [3 x [162 x [161 x [161 x double]]]]]], align 16
+  store ptr %lhs, ptr %rhs, align 8
+  %0 = call i32 @baz()
+  call void @bar(i64 0, i64 0, i64 0, i64 0, i64 0, ptr null, ptr %rhs, ptr null, ptr %rhs)
+; CHECK: call{{.*}}bar
+; CHECK: addq{{.*}}$2147483647, %rsp
+; CHECK: addq{{.*}}$372037585, %rsp
+  ret void
+}
+
+declare void @bar(i64, i64, i64, i64, i64, ptr, ptr, ptr, ptr)
+
+declare i32 @baz()
+
+
+; RUN: llvm-mc -triple x86_64-unknown-unknown %t.s
----------------
macurtis-amd wrote:

@phoebewang Thanks for taking a look at this.

> What's this checking for?

Added comment with rationale:

```
; Double-check that we are able to assemble the generated '.s'. A symptom of the
; problem that led to this test is an assembler failure when using
; '-save-temps'. For example:
;
; > ...s:683:7: error: invalid operand for instruction
; >        addq    $2147483679, %rsp               # imm = 0x8000001F
;
; RUN: llvm-mc -triple x86_64-unknown-unknown %t.s
```

> Why don't put it in the beginning of the file?

Moved to to top of the file.

https://github.com/llvm/llvm-project/pull/125007