[llvm] 327f1ad - [AArch64] Ensure FPR128 callee-save stack offsets are aligned (#184314)
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Sun Mar 8 01:38:48 PST 2026
Author: Benjamin Maxwell
Date: 2026-03-08T09:38:42Z
New Revision: 327f1adef8df6afc07f6c88cfa380c97399af3dc
URL: https://github.com/llvm/llvm-project/commit/327f1adef8df6afc07f6c88cfa380c97399af3dc
DIFF: https://github.com/llvm/llvm-project/commit/327f1adef8df6afc07f6c88cfa380c97399af3dc.diff
LOG: [AArch64] Ensure FPR128 callee-save stack offsets are aligned (#184314)
This was benign for Linux targets (as when dividing by the scale the
offset would be correctly truncated), so only resulted in failures with
`-DLLVM_ENABLE_ASSERTIONS=On`. On Windows, this was a miscompile as the
lack of alignment would result in the FPR128 callee-save getting
assigned to the same offset as the previous GPR.
Fixes: #183708
Added:
llvm/test/CodeGen/AArch64/framelayout-fpr128-csr.ll
llvm/test/CodeGen/AArch64/framelayout-fpr128-spill.mir
Modified:
llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index e524c98984ee7..6790b80086136 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -1730,6 +1730,12 @@ void computeCalleeSaveRegisterPairs(const AArch64FrameLowering &AFL,
Register LastReg = 0;
bool HasCSHazardPadding = AFI->hasStackHazardSlotIndex() && !SplitPPRs;
+ auto AlignOffset = [StackFillDir](int Offset, int Align) {
+ if (StackFillDir < 0)
+ return alignDown(Offset, Align);
+ return alignTo(Offset, Align);
+ };
+
// When iterating backwards, the loop condition relies on unsigned wraparound.
for (unsigned i = FirstReg; i < Count; i += RegInc) {
RegPairInfo RPI;
@@ -1844,11 +1850,15 @@ void computeCalleeSaveRegisterPairs(const AArch64FrameLowering &AFL,
RPI.isPaired()) // RPI.FrameIdx must be the lower index of the pair
RPI.FrameIdx = CSI[i + RegInc].getFrameIdx();
- // Realign the scalable offset if necessary. This is relevant when
- // spilling predicates on Windows.
- if (RPI.isScalable() && ScalableByteOffset % Scale != 0) {
- ScalableByteOffset = alignTo(ScalableByteOffset, Scale);
- }
+ // Realign the scalable offset if necessary. This is relevant when spilling
+ // predicates on Windows.
+ if (RPI.isScalable() && ScalableByteOffset % Scale != 0)
+ ScalableByteOffset = AlignOffset(ScalableByteOffset, Scale);
+
+ // Realign the fixed offset if necessary. This is relevant when spilling Q
+ // registers after spilling an odd amount of X registers.
+ if (!RPI.isScalable() && ByteOffset % Scale != 0)
+ ByteOffset = AlignOffset(ByteOffset, Scale);
int OffsetPre = RPI.isScalable() ? ScalableByteOffset : ByteOffset;
assert(OffsetPre % Scale == 0);
diff --git a/llvm/test/CodeGen/AArch64/framelayout-fpr128-csr.ll b/llvm/test/CodeGen/AArch64/framelayout-fpr128-csr.ll
new file mode 100644
index 0000000000000..09bfbc5d4c82b
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/framelayout-fpr128-csr.ll
@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -verify-machineinstrs -mtriple=aarch64-none-linux-gnu < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -mtriple=aarch64-windows-msvc < %s | FileCheck %s --check-prefix=CHECK-WINDOWS
+
+; The purpose of this test is to verify q8 is assigned a 16-byte aligned offset
+; after the x10 is assigned an offset. The CSR (on Linux) are assigned offsets
+; in the order GPRs then FPRs. The stack size of this function is 48
+; (alignTo((16 + 8 * 3), 16)), so after x8 is given the offset 24, q8 originally
+; would be assigned offset 8, which is not 16-byte aligned.
+define preserve_allcc void @d(ptr %ptr) nounwind {
+; CHECK-LABEL: d:
+; CHECK: // %bb.0: // %entry
+; CHECK-NEXT: str q8, [sp, #-32]! // 16-byte Folded Spill
+; CHECK-NEXT: str x10, [sp, #24] // 8-byte Spill
+; CHECK-NEXT: //APP
+; CHECK-NEXT: //NO_APP
+; CHECK-NEXT: ldr x10, [sp, #24] // 8-byte Reload
+; CHECK-NEXT: ldr q8, [sp], #32 // 16-byte Folded Reload
+; CHECK-NEXT: ret
+;
+; CHECK-WINDOWS-LABEL: d:
+; CHECK-WINDOWS: // %bb.0: // %entry
+; CHECK-WINDOWS-NEXT: str x10, [sp, #-32]! // 8-byte Folded Spill
+; CHECK-WINDOWS-NEXT: str q8, [sp, #16] // 16-byte Spill
+; CHECK-WINDOWS-NEXT: //APP
+; CHECK-WINDOWS-NEXT: //NO_APP
+; CHECK-WINDOWS-NEXT: ldr q8, [sp, #16] // 16-byte Reload
+; CHECK-WINDOWS-NEXT: ldr x10, [sp], #32 // 8-byte Folded Reload
+; CHECK-WINDOWS-NEXT: ret
+entry:
+ tail call void asm sideeffect "", "~{x10},~{q8}"()
+ ret void
+}
diff --git a/llvm/test/CodeGen/AArch64/framelayout-fpr128-spill.mir b/llvm/test/CodeGen/AArch64/framelayout-fpr128-spill.mir
new file mode 100644
index 0000000000000..a6236bd917129
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/framelayout-fpr128-spill.mir
@@ -0,0 +1,38 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 6
+# RUN: llc -mtriple=aarch64-linux-gnu -run-pass=prologepilog %s -o - | FileCheck %s
+# RUN: llc -mtriple=aarch64-windows-msvc -run-pass=prologepilog %s -o - | FileCheck %s --check-prefix=CHECK-WINDOWS
+
+--- |
+ ; Tests Q8 is assigned a 16-byte aligned offset after X10 is assigned an offset.
+ define preserve_allcc void @test_fpr128_spill_alignment() nounwind { entry: unreachable }
+...
+---
+name: test_fpr128_spill_alignment
+tracksRegLiveness: true
+body: |
+ bb.0:
+ ; CHECK-LABEL: name: test_fpr128_spill_alignment
+ ; CHECK: liveins: $q8, $x10
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: early-clobber $sp = frame-setup STRQpre killed $q8, $sp, -32 :: (store (s128) into %stack.1)
+ ; CHECK-NEXT: frame-setup STRXui killed $x10, $sp, 3 :: (store (s64) into %stack.0)
+ ; CHECK-NEXT: $q8 = IMPLICIT_DEF
+ ; CHECK-NEXT: $x10 = IMPLICIT_DEF
+ ; CHECK-NEXT: $x10 = frame-destroy LDRXui $sp, 3 :: (load (s64) from %stack.0)
+ ; CHECK-NEXT: early-clobber $sp, $q8 = frame-destroy LDRQpost $sp, 32 :: (load (s128) from %stack.1)
+ ; CHECK-NEXT: RET_ReallyLR
+ ;
+ ; CHECK-WINDOWS-LABEL: name: test_fpr128_spill_alignment
+ ; CHECK-WINDOWS: liveins: $x10, $q8
+ ; CHECK-WINDOWS-NEXT: {{ $}}
+ ; CHECK-WINDOWS-NEXT: early-clobber $sp = frame-setup STRXpre killed $x10, $sp, -32 :: (store (s64) into %stack.1)
+ ; CHECK-WINDOWS-NEXT: frame-setup STRQui killed $q8, $sp, 1 :: (store (s128) into %stack.0)
+ ; CHECK-WINDOWS-NEXT: $q8 = IMPLICIT_DEF
+ ; CHECK-WINDOWS-NEXT: $x10 = IMPLICIT_DEF
+ ; CHECK-WINDOWS-NEXT: $q8 = frame-destroy LDRQui $sp, 1 :: (load (s128) from %stack.0)
+ ; CHECK-WINDOWS-NEXT: early-clobber $sp, $x10 = frame-destroy LDRXpost $sp, 32 :: (load (s64) from %stack.1)
+ ; CHECK-WINDOWS-NEXT: RET_ReallyLR
+ $q8 = IMPLICIT_DEF
+ $x10 = IMPLICIT_DEF
+ RET_ReallyLR
+...
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