[llvm] [PAC][CodeGen] Do not emit trivial 'mov xN xN' on tail call (PR #109100)
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Wed Sep 18 03:28:05 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-aarch64
Author: Daniil Kovalev (kovdan01)
<details>
<summary>Changes</summary>
Under some conditions, a trivial `mov xN xN` instruction was emitted on tail calls. Consider the following code:
```
class Test {
public:
virtual void f() {}
};
void call_f(Test *t) {
t->f();
}
```
Correponding assembly:
```
_Z6call_fP4Test:
ldr x16, [x0]
mov x17, x0
movk x17, #<!-- -->6503, lsl #<!-- -->48
autda x16, x17
ldr x1, [x16]
=====> mov x16, x16
movk x16, #<!-- -->54167, lsl #<!-- -->48
braa x1, x16
```
This patch makes such movs being omitted.
Co-authored-by: Anatoly Trosinenko <atrosinenko@<!-- -->accesssoftek.com>
---
Full diff: https://github.com/llvm/llvm-project/pull/109100.diff
2 Files Affected:
- (modified) llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp (+6-5)
- (modified) llvm/test/CodeGen/AArch64/ptrauth-call.ll (+22)
``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
index b8f9b58a216446..c6e88131d5a343 100644
--- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -2510,11 +2510,12 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
unsigned DiscReg = AddrDisc;
if (Disc) {
if (AddrDisc != AArch64::NoRegister) {
- EmitToStreamer(*OutStreamer, MCInstBuilder(AArch64::ORRXrs)
- .addReg(ScratchReg)
- .addReg(AArch64::XZR)
- .addReg(AddrDisc)
- .addImm(0));
+ if (ScratchReg != AddrDisc)
+ EmitToStreamer(*OutStreamer, MCInstBuilder(AArch64::ORRXrs)
+ .addReg(ScratchReg)
+ .addReg(AArch64::XZR)
+ .addReg(AddrDisc)
+ .addImm(0));
EmitToStreamer(*OutStreamer, MCInstBuilder(AArch64::MOVKXi)
.addReg(ScratchReg)
.addReg(ScratchReg)
diff --git a/llvm/test/CodeGen/AArch64/ptrauth-call.ll b/llvm/test/CodeGen/AArch64/ptrauth-call.ll
index 9f211b6e1796e6..c3a2a2b0431300 100644
--- a/llvm/test/CodeGen/AArch64/ptrauth-call.ll
+++ b/llvm/test/CodeGen/AArch64/ptrauth-call.ll
@@ -167,6 +167,28 @@ define i32 @test_tailcall_ib_var(ptr %arg0, ptr %arg1) #0 {
ret i32 %tmp1
}
+define void @test_tailcall_omit_mov_x16_x16(ptr %t) {
+; CHECK-LABEL: test_tailcall_omit_mov_x16_x16:
+; CHECK: ldr x16, [x0]
+; CHECK: mov x17, x0
+; CHECK: movk x17, #6503, lsl #48
+; CHECK: autda x16, x17
+; CHECK: ldr x1, [x16]
+; CHECK: movk x16, #54167, lsl #48
+; CHECK: braa x1, x16
+entry:
+ %vtable = load ptr, ptr %t, align 8
+ %0 = ptrtoint ptr %t to i64
+ %1 = tail call i64 @llvm.ptrauth.blend(i64 %0, i64 6503)
+ %2 = ptrtoint ptr %vtable to i64
+ %3 = tail call i64 @llvm.ptrauth.auth(i64 %2, i32 2, i64 %1)
+ %4 = inttoptr i64 %3 to ptr
+ %5 = load ptr, ptr %4, align 8
+ %6 = tail call i64 @llvm.ptrauth.blend(i64 %3, i64 54167)
+ tail call void %5(ptr %t) [ "ptrauth"(i32 0, i64 %6) ]
+ ret void
+}
+
define i32 @test_call_ia_arg(ptr %arg0, i64 %arg1) #0 {
; DARWIN-LABEL: test_call_ia_arg:
; DARWIN-NEXT: stp x29, x30, [sp, #-16]!
``````````
</details>
https://github.com/llvm/llvm-project/pull/109100
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