[TargetPassConfig] Add a hook to tell whether GlobalISel should warm …

…on fallback.

Thanks to this patch, we know have a way to easly see if GlobalISel
failed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280273 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/TargetPassConfig.h

@@ -286,6 +286,11 @@ class TargetPassConfig : public ImmutablePass {
   /// erroring out.
   virtual bool isGlobalISelAbortEnabled() const;
 
+  /// Check whether or not a diagnostic should be emitted when GlobalISel
+  /// uses the fallback path. In other words, it will emit a diagnostic
+  /// when GlobalISel failed and isGlobalISelAbortEnabled is false.
+  virtual bool reportDiagnosticWhenGlobalISelFallback() const;
+
 protected:
   // Helper to verify the analysis is really immutable.
   void setOpt(bool &Opt, bool Val);

lib/CodeGen/LLVMTargetMachine.cpp

@@ -169,7 +169,8 @@ addPassesToGenerateCode(LLVMTargetMachine *TM, PassManagerBase &PM,
       return nullptr;
 
     // Pass to reset the MachineFunction if the ISel failed.
-    PM.add(createResetMachineFunctionPass());
+    PM.add(createResetMachineFunctionPass(
+        PassConfig->reportDiagnosticWhenGlobalISelFallback()));
 
     // Provide a fallback path when we do not want to abort on
     // not-yet-supported input.

lib/CodeGen/TargetPassConfig.cpp

@@ -98,11 +98,13 @@ PrintMachineInstrs("print-machineinstrs", cl::ValueOptional,
                    cl::desc("Print machine instrs"),
                    cl::value_desc("pass-name"), cl::init("option-unspecified"));
 
-static cl::opt<bool> EnableGlobalISelAbort(
+static cl::opt<int> EnableGlobalISelAbort(
     "global-isel-abort", cl::Hidden,
     cl::desc("Enable abort calls when \"global\" instruction selection "
-             "fails to lower/select an instruction"),
-    cl::init(true));
+             "fails to lower/select an instruction: 0 disable the abort, "
+             "1 enable the abort, and "
+             "2 disable the abort but emit a diagnostic on failure"),
+    cl::init(1));
 
 // Temporary option to allow experimenting with MachineScheduler as a post-RA
 // scheduler. Targets can "properly" enable this with
@@ -899,5 +901,9 @@ void TargetPassConfig::addBlockPlacement() {
 /// GlobalISel Configuration
 //===---------------------------------------------------------------------===//
 bool TargetPassConfig::isGlobalISelAbortEnabled() const {
-  return EnableGlobalISelAbort;
+  return EnableGlobalISelAbort == 1;
+}
+
+bool TargetPassConfig::reportDiagnosticWhenGlobalISelFallback() const {
+  return EnableGlobalISelAbort == 2;
 }

test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll

@@ -1,5 +1,6 @@
 ; RUN: not llc -O0 -global-isel -verify-machineinstrs %s -o - 2>&1 | FileCheck %s --check-prefix=ERROR
-; RUN: llc -O0 -global-isel -global-isel-abort=false -verify-machineinstrs %s -o - 2>&1 | FileCheck %s --check-prefix=FALLBACK
+; RUN: llc -O0 -global-isel -global-isel-abort=0 -verify-machineinstrs %s -o - 2>&1 | FileCheck %s --check-prefix=FALLBACK
+; RUN: llc -O0 -global-isel -global-isel-abort=2 -verify-machineinstrs %s -o - 2>&1 | FileCheck %s --check-prefix=FALLBACK_WITH_REPORT
 ; This file checks that the fallback path to selection dag works.
 ; The test is fragile in the sense that it must be updated to expose
 ; something that fails with global-isel.
@@ -12,6 +13,8 @@ target triple = "aarch64-apple-ios"
 ; ERROR: Unable to lower arguments
 ; FALLBACK: ldr q0,
 ; FALLBACK-NEXT: bl ___fixunstfti
+;
+; FALLBACK_WITH_REPORT-DAG: bl ___fixunstfti
 define i128 @ABIi128(i128 %arg1) {
   %farg1 =       bitcast i128 %arg1 to fp128 
   %res = fptoui fp128 %farg1 to i128