Add -disable-builtin option to opt

[dim]

Summary

The option allows to disable specific target library builtin functions,
instead of -disable-simplify-libcalls, which disables all of them.

This is a prerequisite for D70143, which fixes PR43081.

[efriedma]

LGTM

llvm/test/Transforms/InstCombine/disable-builtin.ll

+; Test that -disable-builtin works correctly.
+;
+; RUN: opt < %s -instcombine -disable-builtin strcat -S | FileCheck %s
+;
+; RUN: not opt < %s -instcombine -disable-builtin foobar -S 2>&1 | FileCheck --check-prefix=FOOBAR %s
+; FOOBAR: cannot disable nonexistent builtin function foobar
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+@empty = constant [1 x i8] c"\00", align 1
+
+declare i8* @strcat(i8*, i8*)
+
+define i8* @test_strcat(i8* %x) {
+; CHECK-LABEL: @test_strcat(
+  %empty = getelementptr [1 x i8], [1 x i8]* @empty, i32 0, i32 0
+  %ret = call i8* @strcat(i8* %x, i8* %empty)
+  ret i8* %ret
+; CHECK: call i8* @strcat
+}
+

llvm/tools/opt/opt.cpp

 
 static cl::opt<bool> EmitModuleHash("module-hash", cl::desc("Emit module hash"),
                                     cl::init(false));
 
 static cl::opt<bool>
 DisableSimplifyLibCalls("disable-simplify-libcalls",
                         cl::desc("Disable simplify-libcalls"));
 
+static cl::list<std::string>
+DisableBuiltins("disable-builtin",
+                cl::desc("Disable specific target library builtin function"),
+                cl::ZeroOrMore);
+
+
 static cl::opt<bool>
 Quiet("q", cl::desc("Obsolete option"), cl::Hidden);
 
 static cl::alias
 QuietA("quiet", cl::desc("Alias for -q"), cl::aliasopt(Quiet));
 
 static cl::opt<bool>
 AnalyzeOnly("analyze", cl::desc("Only perform analysis, no optimization"));
#endif
   bool AddOneTimeDebugifyPasses = EnableDebugify && !DebugifyEach;
 
   // Add an appropriate TargetLibraryInfo pass for the module's triple.
   TargetLibraryInfoImpl TLII(ModuleTriple);
 
   // The -disable-simplify-libcalls flag actually disables all builtin optzns.
   if (DisableSimplifyLibCalls)
     TLII.disableAllFunctions();
+  else {
+    // Disable individual builtin functions in TargetLibraryInfo.
+    LibFunc F;
+    for (auto &FuncName : DisableBuiltins)
+      if (TLII.getLibFunc(FuncName, F))
+        TLII.setUnavailable(F);
+      else {
+        errs() << argv[0] << ": cannot disable nonexistent builtin function "
+               << FuncName << '\n';
+        return 1;
+      }
+  }
+
   Passes.add(new TargetLibraryInfoWrapperPass(TLII));
 
   // Add internal analysis passes from the target machine.
   Passes.add(createTargetTransformInfoWrapperPass(TM ? TM->getTargetIRAnalysis()
                                                      : TargetIRAnalysis()));
 
   if (AddOneTimeDebugifyPasses)
     Passes.add(createDebugifyModulePass());