[llvm-branch-commits] Reapply "[llvm][RISCV] Enable trailing fences for seq-cst stores by default (#87376)" (PR #90267)
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Fri Apr 26 13:52:23 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-risc-v
Author: Paul Kirth (ilovepi)
<details>
<summary>Changes</summary>
With the tag merging in place, we can safely change the default for
+seq-cst-trailing-fence to the default, according to the recommendation in
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-atomic.adoc
This tag changes the default for the feature flag, and moves to more
consistent naming with respect to existing features.
This was reverted with https://github.com/llvm/llvm-project/pull/84597,
because ld.bfd would segfault with unknown riscv attributes.
---
Full diff: https://github.com/llvm/llvm-project/pull/90267.diff
7 Files Affected:
- (modified) llvm/docs/ReleaseNotes.rst (+5)
- (modified) llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp (+3-3)
- (modified) llvm/lib/Target/RISCV/RISCVFeatures.td (+4-4)
- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+1-1)
- (modified) llvm/test/CodeGen/RISCV/atomic-load-store.ll (+8-8)
- (modified) llvm/test/CodeGen/RISCV/attributes.ll (+2-2)
- (modified) llvm/test/CodeGen/RISCV/forced-atomics.ll (+6-6)
``````````diff
diff --git a/llvm/docs/ReleaseNotes.rst b/llvm/docs/ReleaseNotes.rst
index a83b8bb79a1c99..3e92cae9869d38 100644
--- a/llvm/docs/ReleaseNotes.rst
+++ b/llvm/docs/ReleaseNotes.rst
@@ -113,6 +113,11 @@ Changes to the RISC-V Backend
* The experimental Ssqosid extension is supported.
* Zacas is no longer experimental.
* Added the CSR names from the Resumable Non-Maskable Interrupts (Smrnmi) extension.
+* The default atomics mapping was changed to emit an additional trailing fence
+ for sequentially consistent stores, offering compatibility with a future
+ mapping using load-acquire and store-release instructions while remaining
+ fully compatible with objects produced prior to this change. The mapping
+ (ABI) used is recorded as an ELF attribute.
Changes to the WebAssembly Backend
----------------------------------
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
index 6f5f12cc72862d..adb17cec28c26f 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp
@@ -77,9 +77,9 @@ void RISCVTargetStreamer::emitTargetAttributes(const MCSubtargetInfo &STI,
}
if (STI.hasFeature(RISCV::FeatureStdExtA)) {
- unsigned AtomicABITag = STI.hasFeature(RISCV::FeatureTrailingSeqCstFence)
- ? RISCVAttrs::RISCVAtomicAbiTag::AtomicABI::A6S
- : RISCVAttrs::RISCVAtomicAbiTag::AtomicABI::A6C;
+ unsigned AtomicABITag = STI.hasFeature(RISCV::FeatureNoTrailingSeqCstFence)
+ ? RISCVAttrs::RISCVAtomicAbiTag::AtomicABI::A6C
+ : RISCVAttrs::RISCVAtomicAbiTag::AtomicABI::A6S;
emitAttribute(RISCVAttrs::ATOMIC_ABI, AtomicABITag);
}
}
diff --git a/llvm/lib/Target/RISCV/RISCVFeatures.td b/llvm/lib/Target/RISCV/RISCVFeatures.td
index c3dc4ea53697c0..deb983528f323c 100644
--- a/llvm/lib/Target/RISCV/RISCVFeatures.td
+++ b/llvm/lib/Target/RISCV/RISCVFeatures.td
@@ -1216,10 +1216,10 @@ foreach i = {1-31} in
def FeatureSaveRestore : SubtargetFeature<"save-restore", "EnableSaveRestore",
"true", "Enable save/restore.">;
-def FeatureTrailingSeqCstFence : SubtargetFeature<"seq-cst-trailing-fence",
- "EnableSeqCstTrailingFence",
- "true",
- "Enable trailing fence for seq-cst store.">;
+def FeatureNoTrailingSeqCstFence : SubtargetFeature<"no-trailing-seq-cst-fence",
+ "EnableTrailingSeqCstFence",
+ "false",
+ "Disable trailing fence for seq-cst store.">;
def FeatureUnalignedScalarMem
: SubtargetFeature<"unaligned-scalar-mem", "EnableUnalignedScalarMem",
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 539aa352554503..769c465d56f984 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -20192,7 +20192,7 @@ Instruction *RISCVTargetLowering::emitTrailingFence(IRBuilderBase &Builder,
if (isa<LoadInst>(Inst) && isAcquireOrStronger(Ord))
return Builder.CreateFence(AtomicOrdering::Acquire);
- if (Subtarget.enableSeqCstTrailingFence() && isa<StoreInst>(Inst) &&
+ if (Subtarget.enableTrailingSeqCstFence() && isa<StoreInst>(Inst) &&
Ord == AtomicOrdering::SequentiallyConsistent)
return Builder.CreateFence(AtomicOrdering::SequentiallyConsistent);
return nullptr;
diff --git a/llvm/test/CodeGen/RISCV/atomic-load-store.ll b/llvm/test/CodeGen/RISCV/atomic-load-store.ll
index 2d1fc21cda89b0..1586a133568b35 100644
--- a/llvm/test/CodeGen/RISCV/atomic-load-store.ll
+++ b/llvm/test/CodeGen/RISCV/atomic-load-store.ll
@@ -1,26 +1,26 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc -mtriple=riscv32 -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefix=RV32I %s
-; RUN: llc -mtriple=riscv32 -mattr=+a -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv32 -mattr=+a,+no-trailing-seq-cst-fence -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV32IA,RV32IA-WMO %s
-; RUN: llc -mtriple=riscv32 -mattr=+a,+experimental-ztso -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv32 -mattr=+a,+experimental-ztso,+no-trailing-seq-cst-fence -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV32IA,RV32IA-TSO %s
; RUN: llc -mtriple=riscv64 -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefix=RV64I %s
-; RUN: llc -mtriple=riscv64 -mattr=+a -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv64 -mattr=+a,+no-trailing-seq-cst-fence -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV64IA,RV64IA-WMO %s
-; RUN: llc -mtriple=riscv64 -mattr=+a,+experimental-ztso -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv64 -mattr=+a,+experimental-ztso,+no-trailing-seq-cst-fence -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV64IA,RV64IA-TSO %s
-; RUN: llc -mtriple=riscv32 -mattr=+a,+seq-cst-trailing-fence -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv32 -mattr=+a -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV32IA,RV32IA-WMO-TRAILING-FENCE %s
-; RUN: llc -mtriple=riscv32 -mattr=+a,+experimental-ztso,+seq-cst-trailing-fence -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv32 -mattr=+a,+experimental-ztso -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV32IA,RV32IA-TSO-TRAILING-FENCE %s
-; RUN: llc -mtriple=riscv64 -mattr=+a,+seq-cst-trailing-fence -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv64 -mattr=+a -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV64IA,RV64IA-WMO-TRAILING-FENCE %s
-; RUN: llc -mtriple=riscv64 -mattr=+a,+experimental-ztso,+seq-cst-trailing-fence -verify-machineinstrs < %s \
+; RUN: llc -mtriple=riscv64 -mattr=+a,+experimental-ztso -verify-machineinstrs < %s \
; RUN: | FileCheck -check-prefixes=RV64IA,RV64IA-TSO-TRAILING-FENCE %s
diff --git a/llvm/test/CodeGen/RISCV/attributes.ll b/llvm/test/CodeGen/RISCV/attributes.ll
index 1aff3e8b83f401..61b5e50c6d52f2 100644
--- a/llvm/test/CodeGen/RISCV/attributes.ll
+++ b/llvm/test/CodeGen/RISCV/attributes.ll
@@ -129,8 +129,8 @@
; RUN: llc -mtriple=riscv64 -mattr=+m %s -o - | FileCheck --check-prefixes=CHECK,RV64M %s
; RUN: llc -mtriple=riscv64 -mattr=+zmmul %s -o - | FileCheck --check-prefixes=CHECK,RV64ZMMUL %s
; RUN: llc -mtriple=riscv64 -mattr=+m,+zmmul %s -o - | FileCheck --check-prefixes=CHECK,RV64MZMMUL %s
-; RUN: llc -mtriple=riscv64 -mattr=+a %s -o - | FileCheck --check-prefixes=CHECK,RV64A,A6C %s
-; RUN: llc -mtriple=riscv64 -mattr=+a,+seq-cst-trailing-fence %s -o - | FileCheck --check-prefixes=CHECK,RV64A,A6S %s
+; RUN: llc -mtriple=riscv64 -mattr=+a,no-trailing-seq-cst-fence %s -o - | FileCheck --check-prefixes=CHECK,RV64A,A6C %s
+; RUN: llc -mtriple=riscv64 -mattr=+a %s -o - | FileCheck --check-prefixes=CHECK,RV64A,A6S %s
; RUN: llc -mtriple=riscv64 -mattr=+f %s -o - | FileCheck --check-prefixes=CHECK,RV64F %s
; RUN: llc -mtriple=riscv64 -mattr=+d %s -o - | FileCheck --check-prefixes=CHECK,RV64D %s
; RUN: llc -mtriple=riscv64 -mattr=+c %s -o - | FileCheck --check-prefixes=CHECK,RV64C %s
diff --git a/llvm/test/CodeGen/RISCV/forced-atomics.ll b/llvm/test/CodeGen/RISCV/forced-atomics.ll
index f6a53a9d76dd35..35900f8a0717aa 100644
--- a/llvm/test/CodeGen/RISCV/forced-atomics.ll
+++ b/llvm/test/CodeGen/RISCV/forced-atomics.ll
@@ -1,12 +1,12 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -mtriple=riscv32 -mattr=+seq-cst-trailing-fence < %s | FileCheck %s --check-prefixes=RV32,RV32-NO-ATOMIC
+; RUN: llc -mtriple=riscv32 -mattr=+no-trailing-seq-cst-fence < %s | FileCheck %s --check-prefixes=RV32,RV32-NO-ATOMIC
; RUN: llc -mtriple=riscv32 < %s | FileCheck %s --check-prefixes=RV32,RV32-NO-ATOMIC
-; RUN: llc -mtriple=riscv32 -mattr=+forced-atomics < %s | FileCheck %s --check-prefixes=RV32,RV32-ATOMIC
-; RUN: llc -mtriple=riscv32 -mattr=+forced-atomics,+seq-cst-trailing-fence < %s | FileCheck %s --check-prefixes=RV32,RV32-ATOMIC-TRAILING
+; RUN: llc -mtriple=riscv32 -mattr=+forced-atomics,+no-trailing-seq-cst-fence < %s | FileCheck %s --check-prefixes=RV32,RV32-ATOMIC
+; RUN: llc -mtriple=riscv32 -mattr=+forced-atomics < %s | FileCheck %s --check-prefixes=RV32,RV32-ATOMIC-TRAILING
+; RUN: llc -mtriple=riscv64 -mattr=+no-trailing-seq-cst-fence < %s | FileCheck %s --check-prefixes=RV64,RV64-NO-ATOMIC
; RUN: llc -mtriple=riscv64 < %s | FileCheck %s --check-prefixes=RV64,RV64-NO-ATOMIC
-; RUN: llc -mtriple=riscv64 -mattr=+seq-cst-trailing-fence < %s | FileCheck %s --check-prefixes=RV64,RV64-NO-ATOMIC
-; RUN: llc -mtriple=riscv64 -mattr=+forced-atomics < %s | FileCheck %s --check-prefixes=RV64,RV64-ATOMIC
-; RUN: llc -mtriple=riscv64 -mattr=+forced-atomics,+seq-cst-trailing-fence < %s | FileCheck %s --check-prefixes=RV64,RV64-ATOMIC-TRAILING
+; RUN: llc -mtriple=riscv64 -mattr=+forced-atomics,+no-trailing-seq-cst-fence < %s | FileCheck %s --check-prefixes=RV64,RV64-ATOMIC
+; RUN: llc -mtriple=riscv64 -mattr=+forced-atomics < %s | FileCheck %s --check-prefixes=RV64,RV64-ATOMIC-TRAILING
define i8 @load8(ptr %p) nounwind {
; RV32-NO-ATOMIC-LABEL: load8:
``````````
</details>
https://github.com/llvm/llvm-project/pull/90267
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