[AArch64][SME] Only use ADDSVL for SVE stack if there's a streaming body #152323
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It is possible for the SMEPeepeholeOpt pass to optimize out the streaming-mode changes, which for a locally_streaming function essentially removes the streaming body. This means the ADDSVL is unnecessary (and can cause complications for unwindinfo, see llvm#152283 (comment))
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@llvm/pr-subscribers-backend-aarch64 Author: Benjamin Maxwell (MacDue) ChangesIt is possible for the SMEPeepeholeOpt pass to optimize out the streaming-mode changes, which for a locally_streaming function essentially removes the streaming body. This means the ADDSVL is unnecessary (and can cause complications for unwindinfo, see #152283 (comment)) Full diff: https://github.com/llvm/llvm-project/pull/152323.diff 2 Files Affected:
diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index fb59c9f131fb2..66047dccf852d 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -6147,9 +6147,13 @@ void llvm::emitFrameOffset(MachineBasicBlock &MBB,
// vscale in the prologue/epilogue is different the runtime value of vscale
// in the function's body. To avoid having to consider multiple vscales,
// we can use `addsvl` to allocate any scalable stack-slots, which under
- // most circumstances will be only locals, not callee-save slots.
- const Function &F = MBB.getParent()->getFunction();
- bool UseSVL = F.hasFnAttribute("aarch64_pstate_sm_body");
+ // most circumstances will be only locals, not callee-save slots. Note: We
+ // check "hasStreamingModeChanges" here as it is possible for the
+ // SMEPeepeholeOpt pass to optimize out the streaming-mode changes (removing
+ // the streaming body).
+ auto &AFI = *MBB.getParent()->getInfo<AArch64FunctionInfo>();
+ bool UseSVL =
+ AFI.hasStreamingModeChanges() && AFI.getSMEFnAttrs().hasStreamingBody();
int64_t Bytes, NumPredicateVectors, NumDataVectors;
AArch64InstrInfo::decomposeStackOffsetForFrameOffsets(
diff --git a/llvm/test/CodeGen/AArch64/sme-peephole-opts.ll b/llvm/test/CodeGen/AArch64/sme-peephole-opts.ll
index 130a316bcc2ba..213373e00cacf 100644
--- a/llvm/test/CodeGen/AArch64/sme-peephole-opts.ll
+++ b/llvm/test/CodeGen/AArch64/sme-peephole-opts.ll
@@ -314,6 +314,88 @@ define void @test9() "aarch64_pstate_sm_body" {
ret void
}
+; test that if the 'smstart' and 'smtop' are entirely removed in a locally
+; streaming function, we use addvl (not addsvl) for setting up the SVE stack.
+define aarch64_sve_vector_pcs void @test9_1() "aarch64_pstate_sm_body" {
+; CHECK-LABEL: test9_1:
+; CHECK: // %bb.0:
+; CHECK-NEXT: stp x29, x30, [sp, #-16]! // 16-byte Folded Spill
+; CHECK-NEXT: addvl sp, sp, #-18
+; CHECK-NEXT: str p15, [sp, #4, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p14, [sp, #5, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p13, [sp, #6, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p12, [sp, #7, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p11, [sp, #8, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p10, [sp, #9, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p9, [sp, #10, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p8, [sp, #11, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p7, [sp, #12, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p6, [sp, #13, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p5, [sp, #14, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str p4, [sp, #15, mul vl] // 2-byte Folded Spill
+; CHECK-NEXT: str z23, [sp, #2, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z22, [sp, #3, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z21, [sp, #4, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z20, [sp, #5, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z19, [sp, #6, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z18, [sp, #7, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z17, [sp, #8, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z16, [sp, #9, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z15, [sp, #10, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z14, [sp, #11, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z13, [sp, #12, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z12, [sp, #13, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z11, [sp, #14, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z10, [sp, #15, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z9, [sp, #16, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: str z8, [sp, #17, mul vl] // 16-byte Folded Spill
+; CHECK-NEXT: .cfi_escape 0x0f, 0x0a, 0x8f, 0x10, 0x92, 0x2e, 0x00, 0x11, 0x90, 0x01, 0x1e, 0x22 // sp + 16 + 144 * VG
+; CHECK-NEXT: .cfi_offset w30, -8
+; CHECK-NEXT: .cfi_offset w29, -16
+; CHECK-NEXT: .cfi_escape 0x10, 0x48, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x78, 0x1e, 0x22, 0x40, 0x1c // $d8 @ cfa - 8 * VG - 16
+; CHECK-NEXT: .cfi_escape 0x10, 0x49, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x70, 0x1e, 0x22, 0x40, 0x1c // $d9 @ cfa - 16 * VG - 16
+; CHECK-NEXT: .cfi_escape 0x10, 0x4a, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x68, 0x1e, 0x22, 0x40, 0x1c // $d10 @ cfa - 24 * VG - 16
+; CHECK-NEXT: .cfi_escape 0x10, 0x4b, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x60, 0x1e, 0x22, 0x40, 0x1c // $d11 @ cfa - 32 * VG - 16
+; CHECK-NEXT: .cfi_escape 0x10, 0x4c, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x58, 0x1e, 0x22, 0x40, 0x1c // $d12 @ cfa - 40 * VG - 16
+; CHECK-NEXT: .cfi_escape 0x10, 0x4d, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x50, 0x1e, 0x22, 0x40, 0x1c // $d13 @ cfa - 48 * VG - 16
+; CHECK-NEXT: .cfi_escape 0x10, 0x4e, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x48, 0x1e, 0x22, 0x40, 0x1c // $d14 @ cfa - 56 * VG - 16
+; CHECK-NEXT: .cfi_escape 0x10, 0x4f, 0x09, 0x92, 0x2e, 0x00, 0x11, 0x40, 0x1e, 0x22, 0x40, 0x1c // $d15 @ cfa - 64 * VG - 16
+; CHECK-NEXT: bl callee
+; CHECK-NEXT: ldr z23, [sp, #2, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z22, [sp, #3, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z21, [sp, #4, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z20, [sp, #5, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z19, [sp, #6, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z18, [sp, #7, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z17, [sp, #8, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z16, [sp, #9, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z15, [sp, #10, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z14, [sp, #11, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z13, [sp, #12, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z12, [sp, #13, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z11, [sp, #14, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z10, [sp, #15, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z9, [sp, #16, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr z8, [sp, #17, mul vl] // 16-byte Folded Reload
+; CHECK-NEXT: ldr p15, [sp, #4, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p14, [sp, #5, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p13, [sp, #6, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p12, [sp, #7, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p11, [sp, #8, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p10, [sp, #9, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p9, [sp, #10, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p8, [sp, #11, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p7, [sp, #12, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p6, [sp, #13, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p5, [sp, #14, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: ldr p4, [sp, #15, mul vl] // 2-byte Folded Reload
+; CHECK-NEXT: addvl sp, sp, #18
+; CHECK-NEXT: ldp x29, x30, [sp], #16 // 16-byte Folded Reload
+; CHECK-NEXT: ret
+ call void @callee()
+ ret void
+}
+
; similar to above, but in this case only the first
; 'smstart, smstop' pair can be removed and the code required
; for the CFI is still needed.
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sdesmalen-arm
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Aug 6, 2025
sdesmalen-arm
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Aug 8, 2025
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We discussed this offline; SVE locals that have their address passed to a function, even if that call (or any other part of the function) doesn't require a streaming mode change, should still be allocated with addsvl.
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It is possible for the SMEPeepeholeOpt pass to optimize out the streaming-mode changes, which for a locally_streaming function essentially removes the streaming body. This means the ADDSVL is unnecessary (and can cause complications for unwindinfo, see #152283 (comment))