[llvm] [AArch64][GlobalISel] Fix incorrect ABI when tail call not supported (PR #70215)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-globalisel

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

The check for whether a tail call is supported calls determineAssignments(), which may modify argument flags. As such, even though the check fails and a non-tail call will be emitted, it will not have a different (incorrect) ABI.

Fix this by operating on a separate copy of the arguments.

Fixes https://github.com/llvm/llvm-project/issues/70207.

---
Full diff: https://github.com/llvm/llvm-project/pull/70215.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp (+4-1) 
- (modified) llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-tail-call-fallback.ll (+7-11) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp b/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
index 2d6cc870f98e77f..02a0c58c8fd0f64 100644
--- a/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp
@@ -854,7 +854,10 @@ bool AArch64CallLowering::areCalleeOutgoingArgsTailCallable(
 
   AArch64OutgoingValueAssigner CalleeAssigner(AssignFnFixed, AssignFnVarArg,
                                               Subtarget, /*IsReturn*/ false);
-  if (!determineAssignments(CalleeAssigner, OutArgs, OutInfo)) {
+  // determineAssignments() may modify argument flags, so make a copy.
+  SmallVector<ArgInfo, 8> OutArgsCopy;
+  append_range(OutArgsCopy, OutArgs);
+  if (!determineAssignments(CalleeAssigner, OutArgsCopy, OutInfo)) {
     LLVM_DEBUG(dbgs() << "... Could not analyze call operands.\n");
     return false;
   }
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-tail-call-fallback.ll b/llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-tail-call-fallback.ll
index fc6eefb4016b66d..ebd2beca6781050 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-tail-call-fallback.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/call-lowering-tail-call-fallback.ll
@@ -3,30 +3,26 @@
 
 declare void @func(i64, i64, i64, i64, i64, i128, i128)
 
-; FIXME: This is a miscompile.
 ; Make sure the check for whether a tail call is allowed does not affect the
 ; calling convention if it fails.
 ; The first i128 argument should be passed in registers, not on the stack.
 define void @pr70207(i128 %arg1, i128 %arg2) nounwind {
 ; CHECK-LABEL: pr70207:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    sub sp, sp, #64
+; CHECK-NEXT:    mov x8, x2
 ; CHECK-NEXT:    mov x6, x0
-; CHECK-NEXT:    mov x8, x1
-; CHECK-NEXT:    mov x9, x2
-; CHECK-NEXT:    mov x10, x3
+; CHECK-NEXT:    mov x7, x1
+; CHECK-NEXT:    mov x9, x3
 ; CHECK-NEXT:    mov x0, xzr
 ; CHECK-NEXT:    mov x1, xzr
 ; CHECK-NEXT:    mov x2, xzr
 ; CHECK-NEXT:    mov x3, xzr
 ; CHECK-NEXT:    mov x4, xzr
-; CHECK-NEXT:    str x30, [sp, #48] // 8-byte Folded Spill
-; CHECK-NEXT:    str x8, [sp]
-; CHECK-NEXT:    str x9, [sp, #16]
-; CHECK-NEXT:    str x10, [sp, #32]
+; CHECK-NEXT:    str x8, [sp, #-32]!
+; CHECK-NEXT:    stp x9, x30, [sp, #8] // 8-byte Folded Spill
 ; CHECK-NEXT:    bl func
-; CHECK-NEXT:    ldr x30, [sp, #48] // 8-byte Folded Reload
-; CHECK-NEXT:    add sp, sp, #64
+; CHECK-NEXT:    ldr x30, [sp, #16] // 8-byte Folded Reload
+; CHECK-NEXT:    add sp, sp, #32
 ; CHECK-NEXT:    ret
   tail call void @func(i64 0, i64 0, i64 0, i64 0, i64 0, i128 %arg1, i128 %arg2)
   ret void

``````````

</details>


https://github.com/llvm/llvm-project/pull/70215