Merging r323369 and r323371:

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r323369 | aemerson | 2018-01-24 20:59:29 +0100 (Wed, 24 Jan 2018) | 4 lines

[GlobalISel] Don't fall back to FastISel.

Apparently checking the pass structure isn't enough to ensure that we don't fall
back to FastISel, as it's set up as part of the SelectionDAGISel.
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r323371 | aemerson | 2018-01-24 21:35:37 +0100 (Wed, 24 Jan 2018) | 12 lines

[AArch64][GlobalISel] Fall back during AArch64 isel if we have a volatile load.

The tablegen imported patterns for sext(load(a)) don't check for single uses
of the load or delete the original after matching. As a result two loads are
left in the generated code. This particular issue will be fixed by adding
support for a G_SEXTLOAD opcode in future.

There are however other potential issues around this that wouldn't be fixed by
a G_SEXTLOAD, so until we have a proper solution we don't try to handle volatile
loads at all in the AArch64 selector.

Fixes/works around PR36018.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@323434 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 35 insertions, 1 deletions

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index befd797e75b4..bd9fcfb5c1e8 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -1380,8 +1380,10 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
   FastISelFailed = false;
   // Initialize the Fast-ISel state, if needed.
   FastISel *FastIS = nullptr;
-  if (TM.Options.EnableFastISel)
+  if (TM.Options.EnableFastISel) {
+    DEBUG(dbgs() << "Enabling fast-isel\n");
     FastIS = TLI->createFastISel(*FuncInfo, LibInfo);
+  }
 
   setupSwiftErrorVals(Fn, TLI, FuncInfo);
 
diff --git a/lib/CodeGen/TargetPassConfig.cpp b/lib/CodeGen/TargetPassConfig.cpp
index c90a93d7e247..6c91bdc1c524 100644
--- a/lib/CodeGen/TargetPassConfig.cpp
+++ b/lib/CodeGen/TargetPassConfig.cpp
@@ -717,6 +717,8 @@ bool TargetPassConfig::addCoreISelPasses() {
   if (EnableGlobalISel == cl::BOU_TRUE ||
       (EnableGlobalISel == cl::BOU_UNSET && isGlobalISelEnabled() &&
        EnableFastISelOption != cl::BOU_TRUE)) {
+    TM->setFastISel(false);
+
     if (addIRTranslator())
       return true;
 
diff --git a/lib/Target/AArch64/AArch64InstructionSelector.cpp b/lib/Target/AArch64/AArch64InstructionSelector.cpp
index b85b4e082996..2bb9e381073a 100644
--- a/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -929,6 +929,12 @@ bool AArch64InstructionSelector::select(MachineInstr &I,
       return false;
     }
 
+    // FIXME: PR36018: Volatile loads in some cases are incorrectly selected by
+    // folding with an extend. Until we have a G_SEXTLOAD solution bail out if
+    // we hit one.
+    if (Opcode == TargetOpcode::G_LOAD && MemOp.isVolatile())
+      return false;
+
     const unsigned PtrReg = I.getOperand(1).getReg();
 #ifndef NDEBUG
     const RegisterBank &PtrRB = *RBI.getRegBank(PtrReg, MRI, TRI);
diff --git a/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll b/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll
new file mode 100644
index 000000000000..84d8faf62c82
--- /dev/null
+++ b/test/CodeGen/AArch64/GlobalISel/fallback-nofastisel.ll
@@ -0,0 +1,10 @@
+; RUN: llc -mtriple=aarch64_be-- %s -o /dev/null -debug-only=isel -O0 2>&1 | FileCheck %s
+
+; This test uses big endian in order to force an abort since it's not currently supported for GISel.
+; The purpose is to check that we don't fall back to FastISel. Checking the pass structure is insufficient
+; because the FastISel is set up in the SelectionDAGISel, so it doesn't appear on the pass structure.
+
+; CHECK-NOT: Enabling fast-ise
+define void @empty() {
+  ret void
+}
diff --git a/test/CodeGen/AArch64/GlobalISel/irtranslator-volatile-load-pr36018.ll b/test/CodeGen/AArch64/GlobalISel/irtranslator-volatile-load-pr36018.ll
new file mode 100644
index 000000000000..9bda39c9fca7
--- /dev/null
+++ b/test/CodeGen/AArch64/GlobalISel/irtranslator-volatile-load-pr36018.ll
@@ -0,0 +1,14 @@
+; RUN: llc -O0 -mtriple=aarch64-apple-ios -o - %s | FileCheck %s
+
+@g = global i16 0, align 2
+declare void @bar(i32)
+
+; Check that only one load is generated. We fall back to
+define hidden void @foo() {
+; CHECK-NOT: ldrh
+; CHECK: ldrsh
+  %1 = load volatile i16, i16* @g, align 2
+  %2 = sext i16 %1 to i32
+  call void @bar(i32 %2)
+  ret void
+}