[llvm] Use t2LDRLIT_ga_pcrel for loading stack guards with no-movt in PIC mode. (PR #156208)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-arm

Author: Amara Emerson (aemerson)

<details>
<summary>Changes</summary>

When using no-movt we don't use the pcrel version of the literal load.
This change also unifies logic with the ARM version of this function as well,
which has:
```
  if (!Subtarget.useMovt() || ForceELFGOTPIC) {
    // For ELF non-PIC, use GOT PIC code sequence as well because R_ARM_GOT_ABS
    // does not have assembler support.
    if (TM.isPositionIndependent() || ForceELFGOTPIC)
      expandLoadStackGuardBase(MI, ARM::LDRLIT_ga_pcrel, ARM::LDRi12);
    else
      expandLoadStackGuardBase(MI, ARM::LDRLIT_ga_abs, ARM::LDRi12);
    return;
  }
```

rdar://138334512

---
Full diff: https://github.com/llvm/llvm-project/pull/156208.diff


2 Files Affected:

- (modified) llvm/lib/Target/ARM/Thumb2InstrInfo.cpp (+7-3) 
- (modified) llvm/test/CodeGen/ARM/stack-guard-nomovt.ll (+56-20) 


``````````diff
diff --git a/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp b/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp
index 8b254fafc438e..7b9e4f0a55143 100644
--- a/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp
+++ b/llvm/lib/Target/ARM/Thumb2InstrInfo.cpp
@@ -263,11 +263,15 @@ void Thumb2InstrInfo::expandLoadStackGuard(
 
   const auto *GV = cast<GlobalValue>((*MI->memoperands_begin())->getValue());
   const ARMSubtarget &Subtarget = MF.getSubtarget<ARMSubtarget>();
+  bool IsPIC = MF.getTarget().isPositionIndependent();
   if (Subtarget.isTargetELF() && !GV->isDSOLocal())
     expandLoadStackGuardBase(MI, ARM::t2LDRLIT_ga_pcrel, ARM::t2LDRi12);
-  else if (!Subtarget.useMovt())
-    expandLoadStackGuardBase(MI, ARM::tLDRLIT_ga_abs, ARM::t2LDRi12);
-  else if (MF.getTarget().isPositionIndependent())
+  else if (!Subtarget.useMovt()) {
+    expandLoadStackGuardBase(
+        MI, IsPIC ? ARM::t2LDRLIT_ga_pcrel : ARM::tLDRLIT_ga_abs,
+        ARM::t2LDRi12);
+  }
+  else if (IsPIC)
     expandLoadStackGuardBase(MI, ARM::t2MOV_ga_pcrel, ARM::t2LDRi12);
   else
     expandLoadStackGuardBase(MI, ARM::t2MOVi32imm, ARM::t2LDRi12);
diff --git a/llvm/test/CodeGen/ARM/stack-guard-nomovt.ll b/llvm/test/CodeGen/ARM/stack-guard-nomovt.ll
index 6802dabfda87a..2003fd747f43d 100644
--- a/llvm/test/CodeGen/ARM/stack-guard-nomovt.ll
+++ b/llvm/test/CodeGen/ARM/stack-guard-nomovt.ll
@@ -1,27 +1,63 @@
-; RUN: llc -relocation-model=static -mattr=+no-movt < %s | FileCheck %s
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -relocation-model=static -mattr=+no-movt < %s | FileCheck %s --check-prefix=STATIC
+; RUN: llc -relocation-model=pic -mattr=+no-movt < %s | FileCheck %s --check-prefix=PIC
 
 target triple = "thumbv7a-linux-gnueabi"
 
 define i32 @test1() #0 {
-; CHECK-LABEL: test1:
-; CHECK:       @ %bb.0:
-; CHECK-NEXT:    push	{r7, lr}
-; CHECK-NEXT:    sub.w	sp, sp, #1032
-; CHECK-NEXT:    ldr	r0, .LCPI0_0
-; CHECK-NEXT:    ldr	r0, [r0]
-; CHECK-NEXT:    str.w	r0, [sp, #1028]
-; CHECK-NEXT:    add	r0, sp, #4
-; CHECK-NEXT:    bl	foo
-; CHECK-NEXT:    ldr.w	r0, [sp, #1028]
-; CHECK-NEXT:    ldr	r1, .LCPI0_0
-; CHECK-NEXT:    ldr	r1, [r1]
-; CHECK-NEXT:    cmp	r1, r0
-; CHECK-NEXT:    ittt	eq
-; CHECK-NEXT:    moveq	r0, #0
-; CHECK-NEXT:    addeq.w	sp, sp, #1032
-; CHECK-NEXT:    popeq	{r7, pc}
-; CHECK-NEXT:  .LBB0_1:
-; CHECK-NEXT:    bl __stack_chk_fail
+; STATIC-LABEL: test1:
+; STATIC:       @ %bb.0:
+; STATIC-NEXT:    push {r7, lr}
+; STATIC-NEXT:    sub.w sp, sp, #1032
+; STATIC-NEXT:    ldr r0, .LCPI0_0
+; STATIC-NEXT:    ldr r0, [r0]
+; STATIC-NEXT:    str.w r0, [sp, #1028]
+; STATIC-NEXT:    add r0, sp, #4
+; STATIC-NEXT:    bl foo
+; STATIC-NEXT:    ldr.w r0, [sp, #1028]
+; STATIC-NEXT:    ldr r1, .LCPI0_0
+; STATIC-NEXT:    ldr r1, [r1]
+; STATIC-NEXT:    cmp r1, r0
+; STATIC-NEXT:    ittt eq
+; STATIC-NEXT:    moveq r0, #0
+; STATIC-NEXT:    addeq.w sp, sp, #1032
+; STATIC-NEXT:    popeq {r7, pc}
+; STATIC-NEXT:  .LBB0_1:
+; STATIC-NEXT:    bl __stack_chk_fail
+; STATIC-NEXT:    .p2align 2
+; STATIC-NEXT:  @ %bb.2:
+; STATIC-NEXT:  .LCPI0_0:
+; STATIC-NEXT:    .long __stack_chk_guard
+;
+; PIC-LABEL: test1:
+; PIC:       @ %bb.0:
+; PIC-NEXT:    push {r7, lr}
+; PIC-NEXT:    sub.w sp, sp, #1032
+; PIC-NEXT:    ldr r0, .LCPI0_0
+; PIC-NEXT:  .LPC0_0:
+; PIC-NEXT:    add r0, pc
+; PIC-NEXT:    ldr r0, [r0]
+; PIC-NEXT:    str.w r0, [sp, #1028]
+; PIC-NEXT:    add r0, sp, #4
+; PIC-NEXT:    bl foo
+; PIC-NEXT:    ldr.w r0, [sp, #1028]
+; PIC-NEXT:    ldr r1, .LCPI0_1
+; PIC-NEXT:  .LPC0_1:
+; PIC-NEXT:    add r1, pc
+; PIC-NEXT:    ldr r1, [r1]
+; PIC-NEXT:    cmp r1, r0
+; PIC-NEXT:    ittt eq
+; PIC-NEXT:    moveq r0, #0
+; PIC-NEXT:    addeq.w sp, sp, #1032
+; PIC-NEXT:    popeq {r7, pc}
+; PIC-NEXT:  .LBB0_1:
+; PIC-NEXT:    bl __stack_chk_fail
+; PIC-NEXT:    .p2align 2
+; PIC-NEXT:  @ %bb.2:
+; PIC-NEXT:  .LCPI0_0:
+; PIC-NEXT:    .long __stack_chk_guard-(.LPC0_0+4)
+; PIC-NEXT:  .LCPI0_1:
+; PIC-NEXT:    .long __stack_chk_guard-(.LPC0_1+4)
   %a1 = alloca [256 x i32], align 4
   call void @foo(ptr %a1) #3
   ret i32 0

``````````

</details>


https://github.com/llvm/llvm-project/pull/156208