Index: llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
+++ llvm/trunk/lib/CodeGen/TargetPassConfig.cpp
@@ -755,22 +755,33 @@
 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;
Index: llvm/trunk/test/CodeGen/AArch64/GlobalISel/gisel-commandline-option-fastisel.ll
===================================================================
--- llvm/trunk/test/CodeGen/AArch64/GlobalISel/gisel-commandline-option-fastisel.ll
+++ llvm/trunk/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
+}