[llvm] [AArch64] Skip storing of stack arguments when lowering tail calls (PR #126735)

Guy David via llvm-commits llvm-commits at lists.llvm.org
Tue Feb 11 06:27:48 PST 2025


https://github.com/guy-david created https://github.com/llvm/llvm-project/pull/126735

This issue starts in the selection DAG, but without this change, the backend would emit the following for a trivial tail call:
```
ldr w8, [sp]
str w8, [sp]
b func
```

I'm not too sure that checking for immutability of a specific stack object is a good enough of a gurantee, because as soon a tail-call is done lowering,`setHasTailCall()` is called and in that case perhaps a pass is allowed to change the value of the object in-memory?

This can be extended to the ARM backend as well.
Removed the `tailcall` keyword from a few other test assets, I'm assuming their original intent was left intact.

>From b08450df2896519fbf099f2346ba190ed836c56e Mon Sep 17 00:00:00 2001
From: Guy David <guyda96 at gmail.com>
Date: Tue, 11 Feb 2025 14:15:02 +0200
Subject: [PATCH] [AArch64] Skip storing of immutable stack arguments in tail
 calls

---
 .../Target/AArch64/AArch64ISelLowering.cpp    |  19 +++-
 llvm/test/CodeGen/AArch64/darwinpcs-tail.ll   |   4 +-
 .../CodeGen/AArch64/scavenge-large-call.ll    |   2 +-
 .../sve-fixed-length-frame-offests-crash.ll   | 103 +++++++++---------
 .../CodeGen/AArch64/tail-call-stack-args.ll   |  55 ++++++++++
 5 files changed, 126 insertions(+), 57 deletions(-)
 create mode 100644 llvm/test/CodeGen/AArch64/tail-call-stack-args.ll

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 0d1608a97bfd3..2a325dd418788 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -9328,10 +9328,25 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
       }
       unsigned LocMemOffset = VA.getLocMemOffset();
       int32_t Offset = LocMemOffset + BEAlign;
-      SDValue PtrOff = DAG.getIntPtrConstant(Offset, DL);
-      PtrOff = DAG.getNode(ISD::ADD, DL, PtrVT, StackPtr, PtrOff);
 
       if (IsTailCall) {
+        // When the frame pointer is perfectly aligned for the tail call and the
+        // same stack argument is passed down, omit storing it if is immutable
+        // and already in the right offset.
+        if (FPDiff == 0) {
+          if (auto *LoadNode = dyn_cast<LoadSDNode>(Arg)) {
+            if (auto *FINode =
+                    dyn_cast<FrameIndexSDNode>(LoadNode->getBasePtr())) {
+              MachineFrameInfo &MFI = MF.getFrameInfo();
+              int FI = FINode->getIndex();
+              if (LoadNode->getMemoryVT() == VA.getValVT() &&
+                  MFI.isImmutableObjectIndex(FI) &&
+                  Offset == MFI.getObjectOffset(FI))
+                continue;
+            }
+          }
+        }
+
         Offset = Offset + FPDiff;
         int FI = MF.getFrameInfo().CreateFixedObject(OpSize, Offset, true);
 
diff --git a/llvm/test/CodeGen/AArch64/darwinpcs-tail.ll b/llvm/test/CodeGen/AArch64/darwinpcs-tail.ll
index 5d3c755d0d73d..61c25edded2ac 100644
--- a/llvm/test/CodeGen/AArch64/darwinpcs-tail.ll
+++ b/llvm/test/CodeGen/AArch64/darwinpcs-tail.ll
@@ -5,11 +5,11 @@
 
 ; CHECK-LABEL: __ZThn16_N1C3addEPKcz:
 ; CHECK:       b __ZN1C3addEPKcz
+
 ; CHECK-LABEL: _tailTest:
 ; CHECK:       b __ZN1C3addEPKcz
+
 ; CHECK-LABEL: __ZThn8_N1C1fEiiiiiiiiiz:
-; CHECK:       ldr     w9, [sp, #4]
-; CHECK:       str     w9, [sp, #4]
 ; CHECK:       b __ZN1C1fEiiiiiiiiiz
 
 %class.C = type { %class.A.base, [4 x i8], %class.B.base, [4 x i8] }
diff --git a/llvm/test/CodeGen/AArch64/scavenge-large-call.ll b/llvm/test/CodeGen/AArch64/scavenge-large-call.ll
index 0c9bdd098aa2a..0cbdd087a5b96 100644
--- a/llvm/test/CodeGen/AArch64/scavenge-large-call.ll
+++ b/llvm/test/CodeGen/AArch64/scavenge-large-call.ll
@@ -4,7 +4,7 @@
 ; CHECK: add {{x[0-9]+}}, sp,
 
 define void @caller(ptr %0, i16 %1, i16 %2, i8 %3, double %4, i16 %5, i8 %6, ptr %7, double %8, i32 %9, ptr %10, double %11, double %12, [2 x i64] %13, [2 x i64] %14, [2 x i64] %15, double %16, double %17, [2 x i64] %18, [2 x i64] %19, i16 %20, i32 %21, double %22, i8 %23, [2 x i64] %24, [2 x i64] %25, [2 x i64] %26, i8 %27, i16 %28, i16 %29, i16 %30, i32 %31, [2 x i64] %32, [2 x i64] %33, [2 x i64] %34, [2 x i64] %35, [2 x i64] %36, i32 %37, i32 %38) {
-  tail call void @callee(ptr %0, i16 %1, i16 %2, i8 %3, double 0.000000e+00, i16 %5, i8 %6, ptr %7, double 0.000000e+00, i32 %9, ptr %10, double 0.000000e+00, double 0.000000e+00, [2 x i64] %13, [2 x i64] %14, [2 x i64] %15, double 0.000000e+00, double 0.000000e+00, [2 x i64] %18, [2 x i64] %19, i16 %20, i32 %21, double 0.000000e+00, i8 %23, [2 x i64] %24, [2 x i64] %25, [2 x i64] zeroinitializer, i8 %27, i16 0, i16 0, i16 %28, i32 0, [2 x i64] zeroinitializer, [2 x i64] zeroinitializer, [2 x i64] zeroinitializer, [2 x i64] %35, [2 x i64] %36, i32 0, i32 0)
+  call void @callee(ptr %0, i16 %1, i16 %2, i8 %3, double 0.000000e+00, i16 %5, i8 %6, ptr %7, double 0.000000e+00, i32 %9, ptr %10, double 0.000000e+00, double 0.000000e+00, [2 x i64] %13, [2 x i64] %14, [2 x i64] %15, double 0.000000e+00, double 0.000000e+00, [2 x i64] %18, [2 x i64] %19, i16 %20, i32 %21, double 0.000000e+00, i8 %23, [2 x i64] %24, [2 x i64] %25, [2 x i64] zeroinitializer, i8 %27, i16 0, i16 0, i16 %28, i32 0, [2 x i64] zeroinitializer, [2 x i64] zeroinitializer, [2 x i64] zeroinitializer, [2 x i64] %35, [2 x i64] %36, i32 0, i32 0)
   ret void
 }
 
diff --git a/llvm/test/CodeGen/AArch64/sve-fixed-length-frame-offests-crash.ll b/llvm/test/CodeGen/AArch64/sve-fixed-length-frame-offests-crash.ll
index 1bd688d23050b..c4d886336cf68 100644
--- a/llvm/test/CodeGen/AArch64/sve-fixed-length-frame-offests-crash.ll
+++ b/llvm/test/CodeGen/AArch64/sve-fixed-length-frame-offests-crash.ll
@@ -11,67 +11,66 @@ target triple = "aarch64-unknown-linux-gnu"
 define dso_local void @func1(ptr %v1, ptr %v2, ptr %v3, ptr %v4, ptr %v5, ptr %v6, ptr %v7, ptr %v8,
 ; CHECK-LABEL: func1:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    str x29, [sp, #-48]! // 8-byte Folded Spill
-; CHECK-NEXT:    stp x22, x21, [sp, #16] // 16-byte Folded Spill
-; CHECK-NEXT:    stp x20, x19, [sp, #32] // 16-byte Folded Spill
-; CHECK-NEXT:    .cfi_def_cfa_offset 48
-; CHECK-NEXT:    .cfi_offset w19, -8
-; CHECK-NEXT:    .cfi_offset w20, -16
-; CHECK-NEXT:    .cfi_offset w21, -24
-; CHECK-NEXT:    .cfi_offset w22, -32
-; CHECK-NEXT:    .cfi_offset w29, -48
+; CHECK-NEXT:    sub sp, sp, #368
+; CHECK-NEXT:    stp x29, x30, [sp, #336] // 16-byte Folded Spill
+; CHECK-NEXT:    str x28, [sp, #352] // 8-byte Folded Spill
+; CHECK-NEXT:    add x29, sp, #336
+; CHECK-NEXT:    .cfi_def_cfa w29, 32
+; CHECK-NEXT:    .cfi_offset w28, -16
+; CHECK-NEXT:    .cfi_offset w30, -24
+; CHECK-NEXT:    .cfi_offset w29, -32
 ; CHECK-NEXT:    ptrue p0.d
-; CHECK-NEXT:    add x10, sp, #176
-; CHECK-NEXT:    add x8, sp, #48
-; CHECK-NEXT:    add x9, sp, #144
-; CHECK-NEXT:    add x20, sp, #176
-; CHECK-NEXT:    ldr x15, [sp, #104]
-; CHECK-NEXT:    ld1d { z3.d }, p0/z, [x10]
+; CHECK-NEXT:    add x8, x29, #32
+; CHECK-NEXT:    add x9, x29, #136
+; CHECK-NEXT:    mov x12, #32 // =0x20
+; CHECK-NEXT:    ldp x10, x11, [x29, #336]
 ; CHECK-NEXT:    ld1d { z0.d }, p0/z, [x8]
-; CHECK-NEXT:    add x8, sp, #112
-; CHECK-NEXT:    ld1d { z2.d }, p0/z, [x9]
+; CHECK-NEXT:    add x8, x29, #72
+; CHECK-NEXT:    ld1d { z3.d }, p0/z, [x9]
 ; CHECK-NEXT:    ld1d { z1.d }, p0/z, [x8]
-; CHECK-NEXT:    ldur q4, [sp, #88]
-; CHECK-NEXT:    ldp x9, x8, [sp, #328]
-; CHECK-NEXT:    ldr x19, [sp, #272]
-; CHECK-NEXT:    ldp x11, x10, [sp, #312]
-; CHECK-NEXT:    ldp x13, x12, [sp, #296]
-; CHECK-NEXT:    ldp x18, x14, [sp, #280]
-; CHECK-NEXT:    ldp x16, x17, [sp, #208]
-; CHECK-NEXT:    ldp x21, x22, [sp, #352]
-; CHECK-NEXT:    st1d { z3.d }, p0, [x20]
-; CHECK-NEXT:    add x20, sp, #144
-; CHECK-NEXT:    st1d { z2.d }, p0, [x20]
-; CHECK-NEXT:    add x20, sp, #112
-; CHECK-NEXT:    st1d { z1.d }, p0, [x20]
-; CHECK-NEXT:    add x20, sp, #48
-; CHECK-NEXT:    st1d { z0.d }, p0, [x20]
-; CHECK-NEXT:    stp x21, x22, [sp, #352]
-; CHECK-NEXT:    ldp x22, x21, [sp, #16] // 16-byte Folded Reload
-; CHECK-NEXT:    stp x19, x18, [sp, #272]
-; CHECK-NEXT:    ldp x20, x19, [sp, #32] // 16-byte Folded Reload
-; CHECK-NEXT:    stp x16, x17, [sp, #208]
-; CHECK-NEXT:    stur q4, [sp, #88]
-; CHECK-NEXT:    str x15, [sp, #104]
-; CHECK-NEXT:    stp x14, x13, [sp, #288]
-; CHECK-NEXT:    stp x12, x11, [sp, #304]
-; CHECK-NEXT:    stp x10, x9, [sp, #320]
-; CHECK-NEXT:    str x8, [sp, #336]
-; CHECK-NEXT:    ldr x29, [sp], #48 // 8-byte Folded Reload
-; CHECK-NEXT:    b func2
+; CHECK-NEXT:    add x8, x29, #104
+; CHECK-NEXT:    add x9, x29, #288
+; CHECK-NEXT:    ld1d { z2.d }, p0/z, [x8]
+; CHECK-NEXT:    add x8, x29, #168
+; CHECK-NEXT:    ld1d { z6.d }, p0/z, [x9]
+; CHECK-NEXT:    ld1d { z4.d }, p0/z, [x8]
+; CHECK-NEXT:    add x8, x29, #256
+; CHECK-NEXT:    ldr x9, [x29, #320]
+; CHECK-NEXT:    ld1d { z5.d }, p0/z, [x8]
+; CHECK-NEXT:    ldr x8, [x29, #200]
+; CHECK-NEXT:    st1d { z6.d }, p0, [sp, x12, lsl #3]
+; CHECK-NEXT:    mov x12, #28 // =0x1c
+; CHECK-NEXT:    st1d { z5.d }, p0, [sp, x12, lsl #3]
+; CHECK-NEXT:    mov x12, #17 // =0x11
+; CHECK-NEXT:    st1d { z4.d }, p0, [sp, x12, lsl #3]
+; CHECK-NEXT:    mov x12, #13 // =0xd
+; CHECK-NEXT:    st1d { z3.d }, p0, [sp, x12, lsl #3]
+; CHECK-NEXT:    mov x12, #9 // =0x9
+; CHECK-NEXT:    st1d { z2.d }, p0, [sp, x12, lsl #3]
+; CHECK-NEXT:    mov x12, #5 // =0x5
+; CHECK-NEXT:    st1d { z1.d }, p0, [sp, x12, lsl #3]
+; CHECK-NEXT:    st1d { z0.d }, p0, [sp]
+; CHECK-NEXT:    stp x10, x11, [sp, #304]
+; CHECK-NEXT:    str x9, [sp, #288]
+; CHECK-NEXT:    str x8, [sp, #168]
+; CHECK-NEXT:    bl func2
+; CHECK-NEXT:    ldp x29, x30, [sp, #336] // 16-byte Folded Reload
+; CHECK-NEXT:    ldr x28, [sp, #352] // 8-byte Folded Reload
+; CHECK-NEXT:    add sp, sp, #368
+; CHECK-NEXT:    ret
                              ptr %v9, ptr %v10, ptr %v11, ptr %v12, ptr %v13, ptr %v14,  ptr %v15, ptr %v16,
                              ptr %v17, ptr %v18, ptr %v19, ptr %v20, ptr %v21, ptr %v22, ptr %v23, ptr %v24,
                              ptr %v25, ptr %v26, ptr %v27, ptr %v28, ptr %v29, ptr %v30, ptr %v31, ptr %v32,
                              ptr %v33, ptr %v34, ptr %v35, ptr %v36, ptr %v37, ptr %v38, ptr %v39, ptr %v40,
                              ptr %v41, ptr %v42, ptr %v43, ptr %v44, ptr %v45, ptr %v46, ptr %v47, ptr %v48,
                              i64 %v49) #0 {
-  tail call void @func2(ptr %v1, ptr %v2, ptr %v3, ptr %v4, ptr %v5, ptr %v6, ptr %v7, ptr %v8,
-                        ptr %v9, ptr %v10, ptr %v11, ptr %v12, ptr undef, ptr %v14, ptr %v15, ptr %v16,
-                        ptr %v17, ptr %v18, ptr %v19, ptr %v20, ptr %v21, ptr %v22, ptr %v23, ptr %v24,
-                        ptr %v25, ptr %v26, ptr %v27, ptr %v28, ptr %v29, ptr %v30, ptr undef, ptr undef,
-                        ptr undef, ptr undef, ptr undef, ptr undef, ptr %v37, ptr %v38, ptr %v39, ptr %v40,
-                        ptr %v41, ptr %v42, ptr %v43, ptr %v44, ptr %v45, ptr undef, ptr %v47, ptr %v48,
-                        i64 undef)
+  call void @func2(ptr %v1, ptr %v2, ptr %v3, ptr %v4, ptr %v5, ptr %v6, ptr %v7, ptr %v8,
+                   ptr %v9, ptr %v10, ptr %v11, ptr %v12, ptr undef, ptr %v14, ptr %v15, ptr %v16,
+                   ptr %v17, ptr %v18, ptr %v19, ptr %v20, ptr %v21, ptr %v22, ptr %v23, ptr %v24,
+                   ptr %v25, ptr %v26, ptr %v27, ptr %v28, ptr %v29, ptr %v30, ptr undef, ptr undef,
+                   ptr undef, ptr undef, ptr undef, ptr undef, ptr %v37, ptr %v38, ptr %v39, ptr %v40,
+                   ptr %v41, ptr %v42, ptr %v43, ptr %v44, ptr %v45, ptr undef, ptr %v47, ptr %v48,
+                   i64 undef)
   ret void
 }
 
diff --git a/llvm/test/CodeGen/AArch64/tail-call-stack-args.ll b/llvm/test/CodeGen/AArch64/tail-call-stack-args.ll
new file mode 100644
index 0000000000000..bde5df737407a
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/tail-call-stack-args.ll
@@ -0,0 +1,55 @@
+; RUN: llc %s -o - | FileCheck %s
+
+; Tail calls which have stack arguments in the same offsets as the caller do not
+; need to load and store the arguments from the stack.
+
+target triple = "aarch64-none-linux-gnu"
+
+declare i32 @func(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j)
+
+; CHECK-LABEL: wrapper_func:
+define i32 @wrapper_func(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j) {
+  ; CHECK: // %bb.
+  ; CHECK-NEXT: b func
+  %call = tail call i32 @func(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j)
+  ret i32 %call
+}
+
+; CHECK-LABEL: wrapper_func_zero_arg:
+define i32 @wrapper_func_zero_arg(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j) {
+  ; CHECK: // %bb.
+  ; CHECK-NEXT: mov	w0, wzr
+  ; CHECK-NEXT: b func
+  %call = tail call i32 @func(i32 0, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j)
+  ret i32 %call
+}
+
+; CHECK-LABEL: wrapper_func_zero_stack_arg:
+define i32 @wrapper_func_zero_stack_arg(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j) {
+  ; CHECK: // %bb.
+  ; CHECK-NEXT: str wzr, [sp, #8]
+  ; CHECK-NEXT: b func
+  %call = tail call i32 @func(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 0)
+  ret i32 %call
+}
+
+; CHECK-LABEL: wrapper_func_overriden_arg:
+define i32 @wrapper_func_overriden_arg(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j) {
+  ; CHECK: // %bb.
+  ; CHECK-NEXT: mov w1, w0
+  ; CHECK-NEXT: mov w0, wzr
+  ; CHECK-NEXT: b func
+  %call = tail call i32 @func(i32 0, i32 %a, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j)
+  ret i32 %call
+}
+
+; CHECK-LABEL: wrapper_func_overriden_stack_arg:
+define i32 @wrapper_func_overriden_stack_arg(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 %i, i32 %j) {
+  ; CHECK: // %bb.
+  ; CHECK-NEXT: ldr w8, [sp]
+  ; CHECK-NEXT: str wzr, [sp]
+  ; CHECK-NEXT: str w8, [sp, #8]
+  ; CHECK-NEXT: b func
+  %call = tail call i32 @func(i32 %a, i32 %b, i32 %c, i32 %d, i32 %e, i32 %f, i32 %g, i32 %h, i32 0, i32 %i)
+  ret i32 %call
+}



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