Add option to print entire function instead of just the loops for loo… (#123229)

print-after-all is useful for diffing IR between two passes. When one of
the two is a function pass, and the other is a loop pass, the diff
becomes useless. Add an option which prints the entire function for loop
passes.

llvm/include/llvm/IR/PrintPasses.h

@@ -51,6 +51,9 @@ std::vector<std::string> printAfterPasses();
 // Returns true if we should always print the entire module.
 bool forcePrintModuleIR();
 
+// Returns true if we should print the entire function for loop passes.
+bool forcePrintFuncIR();
+
 // Return true if -filter-passes is empty or contains the pass name.
 bool isPassInPrintList(StringRef PassName);
 bool isFilterPassesEmpty();

llvm/lib/Analysis/LoopInfo.cpp

@@ -999,6 +999,18 @@ void llvm::printLoop(Loop &L, raw_ostream &OS, const std::string &Banner) {
     return;
   }
 
+  if (forcePrintFuncIR()) {
+    // handling -print-loop-func-scope.
+    // -print-module-scope overrides this.
+    OS << Banner << " (loop: ";
+    L.getHeader()->printAsOperand(OS, false);
+    OS << ")\n";
+
+    // printing whole function.
+    OS << *L.getHeader()->getParent();
+    return;
+  }
+
   OS << Banner;
 
   auto *PreHeader = L.getLoopPreheader();

llvm/lib/IR/PrintPasses.cpp

@@ -88,6 +88,12 @@ static cl::opt<bool>
                               "always print a module IR"),
                      cl::init(false), cl::Hidden);
 
+static cl::opt<bool> LoopPrintFuncScope(
+    "print-loop-func-scope",
+    cl::desc("When printing IR for print-[before|after]{-all} "
+             "for a loop pass, always print function IR"),
+    cl::init(false), cl::Hidden);
+
 // See the description for -print-changed for an explanation of the use
 // of this option.
 static cl::list<std::string> FilterPasses(
@@ -141,6 +147,8 @@ std::vector<std::string> llvm::printAfterPasses() {
 
 bool llvm::forcePrintModuleIR() { return PrintModuleScope; }
 
+bool llvm::forcePrintFuncIR() { return LoopPrintFuncScope; }
+
 bool llvm::isPassInPrintList(StringRef PassName) {
   static std::unordered_set<std::string> Set(FilterPasses.begin(),
                                              FilterPasses.end());

llvm/test/Other/print-loop-func-scope.ll

@@ -0,0 +1,75 @@
+; This test documents how the IR dumped for loop passes differs with -print-loop-func-scope
+; and -print-module-scope
+;   - Without -print-loop-func-scope, dumps only the loop, with 3 sections- preheader,
+;     loop, and exit blocks
+;   - With -print-loop-func-scope, dumps only the function which contains the loop
+;   - With -print-module-scope, dumps the entire module containing the loop, and disregards
+;     the -print-loop-func-scope flag.
+
+; RUN: opt < %s 2>&1 -disable-output \
+; RUN: 	   -passes=licm -print-after=licm \
+; RUN:	   | FileCheck %s -check-prefix=VANILLA
+; RUN: opt < %s 2>&1 -disable-output \
+; RUN: 	   -passes=licm -print-after=licm -print-loop-func-scope \
+; RUN:	   | FileCheck %s -check-prefix=LOOPFUNC
+; RUN: opt < %s 2>&1 -disable-output \
+; RUN: 	   -passes=licm -print-after=licm -print-module-scope \
+; RUN:	   | FileCheck %s -check-prefix=MODULE
+; RUN: opt < %s 2>&1 -disable-output \
+; RUN: 	   -passes=licm -print-after=licm -print-module-scope -print-loop-func-scope\
+; RUN:	   | FileCheck %s -check-prefix=MODULEWITHLOOP
+
+; VANILLA: IR Dump After LICMPass
+; VANILLA-NOT: define void @foo
+; VANILLA: Preheader:
+; VANILLA: Loop:
+; VANILLA: Exit blocks
+
+; LOOPFUNC: IR Dump After LICMPass
+; LOOPFUNC: (loop:
+; LOOPFUNC: define void @foo
+; LOOPFUNC-NOT: Preheader:
+; LOOPFUNC-NOT: Loop:
+; LOOPFUNC-NOT: Exit blocks
+
+; MODULE: IR Dump After LICMPass
+; MODULE: ModuleID =
+; MODULE: define void @foo
+; MODULE-NOT: Preheader:
+; MODULE-NOT: Loop:
+; MODULE-NOT: Exit blocks
+; MODULE: define void @bar
+; MODULE: declare void @baz(i32)
+
+; MODULEWITHLOOP: IR Dump After LICMPass
+; MODULEWITHLOOP: ModuleID =
+; MODULEWITHLOOP: define void @foo
+; MODULEWITHLOOP-NOT: Preheader:
+; MODULEWITHLOOP-NOT: Loop:
+; MODULEWITHLOOP-NOT: Exit blocks
+; MODULEWITHLOOP: define void @bar
+; MODULEWITHLOOP: declare void @baz(i32)
+
+define void @foo(i32 %n) {
+entry:
+  br label %loop_cond
+
+loop_cond:
+  %i = phi i32 [ 0, %entry ], [ %i_next, %loop_body ]
+  %cmp = icmp slt i32 %i, %n
+  br i1 %cmp, label %loop_body, label %loop_end
+
+loop_body:
+  call void @baz(i32 %i)
+  %i_next = add i32 %i, 1
+  br label %loop_cond
+
+loop_end:
+  ret void
+}
+
+define void @bar() {
+  ret void
+}
+
+declare void @baz(i32)