From 7885d2ca5ae8da146dcb51232ea8754aa07b5708 Mon Sep 17 00:00:00 2001
From: Petr Pavlu <petr.pavlu@arm.com>
Date: Tue, 8 Jan 2019 14:19:06 +0000
Subject: [PATCH] [GlobalISel] Fix choice of instruction selector for AArch64
 at -O0 with -global-isel=0

Commit rL347861 introduced an unintentional change in the behaviour when
compiling for AArch64 at -O0 with -global-isel=0. Previously, explicitly
disabling GlobalISel resulted in using FastISel but an updated condition
in the commit changed it to using SelectionDAG. The patch fixes this
condition and slightly better organizes the code that chooses the
instruction selector.

Fixes PR40131.

Differential Revision: https://reviews.llvm.org/D56266


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350626 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/TargetPassConfig.cpp                   | 35 ++++++++++++++--------
 .../gisel-commandline-option-fastisel.ll           | 35 ++++++++++++++++++++++
 2 files changed, 58 insertions(+), 12 deletions(-)
 create mode 100644 test/CodeGen/AArch64/GlobalISel/gisel-commandline-option-fastisel.ll

diff --git a/lib/CodeGen/TargetPassConfig.cpp b/lib/CodeGen/TargetPassConfig.cpp
index defb165fe0f..28126fcf766 100644
--- a/lib/CodeGen/TargetPassConfig.cpp
+++ b/lib/CodeGen/TargetPassConfig.cpp
@@ -755,22 +755,33 @@ void TargetPassConfig::addISelPrepare() {
 bool TargetPassConfig::addCoreISelPasses() {
   // Enable FastISel with -fast-isel, but allow that to be overridden.
   TM->setO0WantsFastISel(EnableFastISelOption != cl::BOU_FALSE);
-  if (EnableFastISelOption == cl::BOU_TRUE ||
-      (TM->getOptLevel() == CodeGenOpt::None && TM->getO0WantsFastISel() &&
-       !TM->Options.EnableGlobalISel)) {
+
+  // Determine an instruction selector.
+  enum class SelectorType { SelectionDAG, FastISel, GlobalISel };
+  SelectorType Selector;
+
+  if (EnableFastISelOption == cl::BOU_TRUE)
+    Selector = SelectorType::FastISel;
+  else if (EnableGlobalISelOption == cl::BOU_TRUE ||
+           (TM->Options.EnableGlobalISel &&
+            EnableGlobalISelOption != cl::BOU_FALSE))
+    Selector = SelectorType::GlobalISel;
+  else if (TM->getOptLevel() == CodeGenOpt::None && TM->getO0WantsFastISel())
+    Selector = SelectorType::FastISel;
+  else
+    Selector = SelectorType::SelectionDAG;
+
+  // Set consistently TM->Options.EnableFastISel and EnableGlobalISel.
+  if (Selector == SelectorType::FastISel) {
     TM->setFastISel(true);
     TM->setGlobalISel(false);
-  }
-
-  // Ask the target for an instruction selector.
-  // Explicitly enabling fast-isel should override implicitly enabled
-  // global-isel.
-  if (EnableGlobalISelOption == cl::BOU_TRUE ||
-      (EnableGlobalISelOption == cl::BOU_UNSET &&
-       TM->Options.EnableGlobalISel && EnableFastISelOption != cl::BOU_TRUE)) {
-    TM->setGlobalISel(true);
+  } else if (Selector == SelectorType::GlobalISel) {
     TM->setFastISel(false);
+    TM->setGlobalISel(true);
+  }
 
+  // Add instruction selector passes.
+  if (Selector == SelectorType::GlobalISel) {
     SaveAndRestore<bool> SavedAddingMachinePasses(AddingMachinePasses, true);
     if (addIRTranslator())
       return true;
diff --git a/test/CodeGen/AArch64/GlobalISel/gisel-commandline-option-fastisel.ll b/test/CodeGen/AArch64/GlobalISel/gisel-commandline-option-fastisel.ll
new file mode 100644
index 00000000000..73158f54325
--- /dev/null
+++ b/test/CodeGen/AArch64/GlobalISel/gisel-commandline-option-fastisel.ll
@@ -0,0 +1,35 @@
+; REQUIRES: asserts
+
+; RUN: llc -mtriple=aarch64-- -debug-pass=Structure %s -o /dev/null 2>&1 \
+; RUN:   -verify-machineinstrs=0 -O0 -global-isel=false -debug-only=isel \
+; RUN:   | FileCheck %s --check-prefixes=DISABLED,FASTISEL
+
+; RUN: llc -mtriple=aarch64-- -debug-pass=Structure %s -o /dev/null 2>&1 \
+; RUN:   -verify-machineinstrs=0 -O1 -global-isel=false -debug-only=isel \
+; RUN:   | FileCheck %s --check-prefixes=DISABLED,NOFASTISEL
+
+; RUN: llc -mtriple=aarch64-- -debug-pass=Structure %s -o /dev/null 2>&1 \
+; RUN:   -verify-machineinstrs=0 -O0 -fast-isel=false -global-isel=false \
+; RUN:   -debug-only=isel \
+; RUN:   | FileCheck %s --check-prefixes=DISABLED,NOFASTISEL
+
+; RUN: llc -mtriple=aarch64-- -debug-pass=Structure %s -o /dev/null 2>&1 \
+; RUN:   -verify-machineinstrs=0 -O1 -fast-isel=false -global-isel=false \
+; RUN:   -debug-only=isel \
+; RUN:   | FileCheck %s --check-prefixes=DISABLED,NOFASTISEL
+
+; Check that the right instruction selector is chosen when using
+; -global-isel=false. FastISel should be used at -O0 (unless -fast-isel=false is
+; also present) and SelectionDAG otherwise.
+
+; DISABLED-NOT: IRTranslator
+
+; DISABLED: AArch64 Instruction Selection
+; DISABLED: Expand ISel Pseudo-instructions
+
+; FASTISEL: Enabling fast-isel
+; NOFASTISEL-NOT: Enabling fast-isel
+
+define void @empty() {
+  ret void
+}
-- 
2.11.0