Don't emit "deprecated instruction in IT block" warning if requested

[kongyi]

Summary

Also fixed formatting in AsmMatcherEmitter because it was confusing.

[kristof.beyls]

GNU binutils has a specific option to silence the warnings about deprecated IT blocks (-m{no-}warn-restrict-it), see https://sourceware.org/legacy-ml/binutils/2019-12/msg00093.html.
I haven't looked up if GNU tools have the equivalent of -no-deprecated-warn.

I also wonder how to specify the "-no-deprecated-warn" option from the clang command line. Is it possible?

Basically, yes, it looks like it's the right thing to also disable warnings related to deprecated IT constructs for -no-deprecated-warn, so this looks like a good change.
But there is probably more to be done to make the option easily accessible from the clang command line and to implement -m{no-}warn-restrict-it for GNU binutils compatibility?

So: this patch LGTM, thanks.

llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp

if (validateInstruction(Inst, Operands)) {
       // tPOP(r8)->t2LDMIA_UPD(sp,r8)->t2STR_POST(sp,r8)
       while (processInstruction(Inst, Operands, Out))
         LLVM_DEBUG(dbgs() << "Changed to: ";
                    Inst.dump_pretty(dbgs(), MII.getName(Inst.getOpcode()));
                    dbgs() << "\n");
 
       // Only after the instruction is fully processed, we can validate it
       if (wasInITBlock && hasV8Ops() && isThumb() &&
-          !isV8EligibleForIT(&Inst)) {
+          !isV8EligibleForIT(&Inst) && !getTargetOptions().MCNoDeprecatedWarn) {
         Warning(IDLoc, "deprecated instruction in IT block");
       }
     }
 
     // Only move forward at the very end so that everything in validate
     // and process gets a consistent answer about whether we're in an IT
     // block.
     forwardITPosition();

llvm/test/MC/ARM/deprecated-v8.s

 @ RUN: llvm-mc -triple armv8 -show-encoding < %s 2>&1 | FileCheck %s --check-prefix=CHECK-ARMV8
 @ RUN: llvm-mc -triple thumbv8 -show-encoding < %s 2>&1 | FileCheck %s --check-prefix=CHECK-THUMBV8
 @ RUN: llvm-mc -triple armv7 -show-encoding < %s 2>&1 | FileCheck %s --check-prefix=CHECK-ARMV7
 @ RUN: llvm-mc -triple thumbv7 -show-encoding < %s 2>&1 | FileCheck %s --check-prefix=CHECK-THUMBV7
 @ RUN: llvm-mc -triple armv6 -show-encoding < %s 2>&1 | FileCheck %s --check-prefix=CHECK-ARMV6
+@ RUN: llvm-mc -triple thumbv8 -show-encoding -no-deprecated-warn < %s 2>&1 | FileCheck %s --check-prefix=CHECK-NO-WARN
 setend be
 @ CHECK-ARMV8: warning: deprecated
 @ CHECK-THUMBV8: warning: deprecated
 @ CHECK-ARMV7-NOT: warning: deprecated
 @ CHECK-THUMBV7-NOT: warning: deprecated
+@ CHECK-NO-WARN-NOT: warning: deprecated
 mcr p15, #0, r5, c7, c5, #4
 @ CHECK-ARMV8: warning: deprecated since v7, use 'isb'
 @ CHECK-THUMBV8: warning: deprecated since v7, use 'isb'
 @ CHECK-ARMV7: warning: deprecated since v7, use 'isb'
 @ CHECK-THUMBV7: warning: deprecated since v7, use 'isb'
 @ CHECK-ARMV6-NOT: warning: deprecated since v7, use 'isb'
+@ CHECK-NO-WARN-NOT: warning: deprecated since v7, use 'isb'
 mcr p15, #0, r5, c7, c10, #4
 @ CHECK-ARMV8: warning: deprecated since v7, use 'dsb'
 @ CHECK-THUMBV8: warning: deprecated since v7, use 'dsb'
 @ CHECK-ARMV7: warning: deprecated since v7, use 'dsb'
 @ CHECK-THUMBV7: warning: deprecated since v7, use 'dsb'
 @ CHECK-ARMV6-NOT: warning: deprecated since v7, use 'dsb'
+@ CHECK-NO-WARN-NOT: warning: deprecated since v7, use 'dsb'
 mcr p15, #0, r5, c7, c10, #5
 @ CHECK-ARMV8: warning: deprecated since v7, use 'dmb'
 @ CHECK-THUMBV8: warning: deprecated since v7, use 'dmb'
 @ CHECK-ARMV7: warning: deprecated since v7, use 'dmb'
 @ CHECK-THUMBV7: warning: deprecated since v7, use 'dmb'
 @ CHECK-ARMV6-NOT: warning: deprecated since v7, use 'dmb'
+@ CHECK-NO-WARN-NOT: warning: deprecated since v7, use 'dmb'
 it ge
 movge r0, #4096
 @ CHECK-THUMBV8: warning: deprecated instruction in IT block
 @ CHECK-THUMBV7-NOT: warning
+@ CHECK-NO-WARN-NOT: warning
 ite ge
 addge r0, r1
 addlt r0, r2
 @ CHECK-ARMV8: warning: applying IT instruction to more than one subsequent instruction is deprecated
 @ CHECK-THUMBV8: warning: applying IT instruction to more than one subsequent instruction is deprecated
 @ CHECK-THUMBV7-NOT: warning
+@ CHECK-NO-WARN-NOT: warning
 it ge
 movge r0, pc // invalid operand
 @ CHECK-THUMBV8: warning: deprecated instruction in IT block
 @ CHECK-THUMBV7-NOT: warning
+@ CHECK-NO-WARN-NOT: warning
 it ge
 revge r0, r0 // invalid instruction
 @ CHECK-THUMBV8: warning: deprecated instruction in IT block
 @ CHECK-THUMBV7-NOT: warning
+@ CHECK-NO-WARN-NOT: warning
 it ge
 clzge r0, r0 // only has 32-bit form
 @ CHECK-THUMBV8: warning: deprecated instruction in IT block
 @ CHECK-THUMBV7-NOT: warning
-
+@ CHECK-NO-WARN-NOT: warning

llvm/utils/TableGen/AsmMatcherEmitter.cpp

#endif
 
   // Call the post-processing function, if used.
   StringRef InsnCleanupFn = AsmParser->getValueAsString("AsmParserInstCleanup");
   if (!InsnCleanupFn.empty())
     OS << "    " << InsnCleanupFn << "(Inst);\n";
 
   if (HasDeprecation) {
     OS << "    std::string Info;\n";
-    OS << "    if (!getParser().getTargetParser().\n";
-    OS << "        getTargetOptions().MCNoDeprecatedWarn &&\n";
+    OS << "    if (!getParser().getTargetParser().getTargetOptions().MCNoDeprecatedWarn &&\n";
     OS << "        MII.getDeprecatedInfo(Inst, getSTI(), Info)) {\n";
     OS << "      SMLoc Loc = ((" << Target.getName()
        << "Operand &)*Operands[0]).getStartLoc();\n";
     OS << "      getParser().Warning(Loc, Info, None);\n";
     OS << "    }\n";
   }
 
   if (!ReportMultipleNearMisses) {