From 74ae778176ec4dc8303e7f0c7dbab973c4c2e97c Mon Sep 17 00:00:00 2001
From: Nemanja Ivanovic <nemanja.i.ibm@gmail.com>
Date: Mon, 17 May 2021 06:05:36 -0500
Subject: [PATCH] [PowerPC] Do not emit dssall on AIX

This instruction is a nop on all server cores (certainly on all
cores that AIX supports) so it is fine to emit a nop instead of it.
In fact, that is exactly what XL emits. So we emit a nop on AIX
and we leave the codegen as is on other platforms since there may
indeed be cores out there for which this actually does some prefetching.
---
 llvm/lib/Target/PowerPC/PPCInstrAltivec.td |  9 ++++++++-
 llvm/lib/Target/PowerPC/PPCInstrInfo.td    |  2 ++
 llvm/test/CodeGen/PowerPC/dssall.ll        | 21 +++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/PowerPC/dssall.ll

diff --git a/llvm/lib/Target/PowerPC/PPCInstrAltivec.td b/llvm/lib/Target/PowerPC/PPCInstrAltivec.td
index 6dfa495..01f898e 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrAltivec.td
+++ b/llvm/lib/Target/PowerPC/PPCInstrAltivec.td
@@ -347,7 +347,7 @@ def DSS      : DSS_Form<0, 822, (outs), (ins u5imm:$STRM),
 }
 
 def DSSALL   : DSS_Form<1, 822, (outs), (ins),
-                        "dssall", IIC_LdStLoad /*FIXME*/, [(int_ppc_altivec_dssall)]>,
+                        "dssall", IIC_LdStLoad /*FIXME*/, []>,
                         Deprecated<DeprecatedDST> {
   let STRM = 0;
   let A = 0;
@@ -865,6 +865,13 @@ def V_SETALLONES  : VXForm_3<908, (outs vrrc:$vD), (ins),
 def : InstAlias<"vmr $vD, $vA", (VOR vrrc:$vD, vrrc:$vA, vrrc:$vA)>;
 def : InstAlias<"vnot $vD, $vA", (VNOR vrrc:$vD, vrrc:$vA, vrrc:$vA)>;
 
+// This is a nop on all supported architectures and the AIX assembler
+// doesn't support it (and will not be updated to support it).
+let Predicates = [IsAIX] in
+def : Pat<(int_ppc_altivec_dssall), (NOP)>;
+let Predicates = [NotAIX] in
+def : Pat<(int_ppc_altivec_dssall), (DSSALL)>;
+
 // Rotates.
 def : Pat<(v16i8 (rotl v16i8:$vA, v16i8:$vB)),
           (v16i8 (VRLB v16i8:$vA, v16i8:$vB))>;
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.td b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
index 7936a4e..b839f38 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.td
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.td
@@ -1178,6 +1178,8 @@ def IsNotISA3_1 : Predicate<"!Subtarget->isISA3_1()">;
 // AIX assembler may not be modern enough to support some extended mne.
 def ModernAs: Predicate<"!Subtarget->isAIXABI() || Subtarget->HasModernAIXAs">, 
                  AssemblerPredicate<(any_of (not AIXOS), FeatureModernAIXAs)>;
+def IsAIX : Predicate<"Subtarget->isAIXABI()">;
+def NotAIX : Predicate<"!Subtarget->isAIXABI()">;
 
 //===----------------------------------------------------------------------===//
 // PowerPC Multiclass Definitions.
diff --git a/llvm/test/CodeGen/PowerPC/dssall.ll b/llvm/test/CodeGen/PowerPC/dssall.ll
new file mode 100644
index 0000000..c33b37c
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/dssall.ll
@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc-ibm-aix-xcoff | \
+; RUN:   FileCheck %s
+; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc64le-- | \
+; RUN:   FileCheck %s --check-prefix=NOTAIX
+define dso_local void @test() local_unnamed_addr {
+; CHECK-LABEL: test:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    nop
+; CHECK-NEXT:    blr
+;
+; NOTAIX-LABEL: test:
+; NOTAIX:       # %bb.0: # %entry
+; NOTAIX-NEXT:    dssall
+; NOTAIX-NEXT:    blr
+entry:
+  tail call void @llvm.ppc.altivec.dssall()
+  ret void
+}
+
+declare void @llvm.ppc.altivec.dssall()
-- 
2.7.4