MIParser/MIRPrinter: Compute block successors if not explicitely specified

- MIParser: If the successor list is not specified successors will be
  added based on basic block operands in the block and possible
  fallthrough.

- MIRPrinter: Adds a new `simplify-mir` option, with that option set:
  Skip printing of block successor lists in cases where the
  parser is guaranteed to reconstruct it. This means we still print the
  list if some successor cannot be determined (happens for example for
  jump tables), if the successor order changes or branch probabilities
  being unequal.

Differential Revision: https://reviews.llvm.org/D31262

llvm-svn: 302289

1 files changed, 35 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/MIRParser/MIParser.cpp b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
index cac22af3295..1d36ff4e145 100644
--- a/llvm/lib/CodeGen/MIRParser/MIParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
@@ -12,11 +12,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "MIParser.h"
+
 #include "MILexer.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/AsmParser/Parser.h"
 #include "llvm/AsmParser/SlotMapping.h"
+#include "llvm/CodeGen/MIRPrinter.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -134,7 +136,8 @@ public:
 
   bool
   parseBasicBlockDefinition(DenseMap<unsigned, MachineBasicBlock *> &MBBSlots);
-  bool parseBasicBlock(MachineBasicBlock &MBB);
+  bool parseBasicBlock(MachineBasicBlock &MBB,
+                       MachineBasicBlock *&AddFalthroughFrom);
   bool parseBasicBlockLiveins(MachineBasicBlock &MBB);
   bool parseBasicBlockSuccessors(MachineBasicBlock &MBB);
 
@@ -518,7 +521,8 @@ bool MIParser::parseBasicBlockSuccessors(MachineBasicBlock &MBB) {
   return false;
 }
 
-bool MIParser::parseBasicBlock(MachineBasicBlock &MBB) {
+bool MIParser::parseBasicBlock(MachineBasicBlock &MBB,
+                               MachineBasicBlock *&AddFalthroughFrom) {
   // Skip the definition.
   assert(Token.is(MIToken::MachineBasicBlockLabel));
   lex();
@@ -538,10 +542,12 @@ bool MIParser::parseBasicBlock(MachineBasicBlock &MBB) {
   //
   // is equivalent to
   //   liveins: %edi, %esi
+  bool ExplicitSuccesors = false;
   while (true) {
     if (Token.is(MIToken::kw_successors)) {
       if (parseBasicBlockSuccessors(MBB))
         return true;
+      ExplicitSuccesors = true;
     } else if (Token.is(MIToken::kw_liveins)) {
       if (parseBasicBlockLiveins(MBB))
         return true;
@@ -557,10 +563,9 @@ bool MIParser::parseBasicBlock(MachineBasicBlock &MBB) {
   // Parse the instructions.
   bool IsInBundle = false;
   MachineInstr *PrevMI = nullptr;
-  while (true) {
-    if (Token.is(MIToken::MachineBasicBlockLabel) || Token.is(MIToken::Eof))
-      return false;
-    else if (consumeIfPresent(MIToken::Newline))
+  while (!Token.is(MIToken::MachineBasicBlockLabel) &&
+         !Token.is(MIToken::Eof)) {
+    if (consumeIfPresent(MIToken::Newline))
       continue;
     if (consumeIfPresent(MIToken::rbrace)) {
       // The first parsing pass should verify that all closing '}' have an
@@ -592,6 +597,22 @@ bool MIParser::parseBasicBlock(MachineBasicBlock &MBB) {
     assert(Token.isNewlineOrEOF() && "MI is not fully parsed");
     lex();
   }
+
+  // Construct successor list by searching for basic block machine operands.
+  if (!ExplicitSuccesors) {
+    SmallVector<MachineBasicBlock*,4> Successors;
+    bool IsFallthrough;
+    guessSuccessors(MBB, Successors, IsFallthrough);
+    for (MachineBasicBlock *Succ : Successors)
+      MBB.addSuccessor(Succ);
+
+    if (IsFallthrough) {
+      AddFalthroughFrom = &MBB;
+    } else {
+      MBB.normalizeSuccProbs();
+    }
+  }
+
   return false;
 }
 
@@ -605,11 +626,18 @@ bool MIParser::parseBasicBlocks() {
   // The first parsing pass should have verified that this token is a MBB label
   // in the 'parseBasicBlockDefinitions' method.
   assert(Token.is(MIToken::MachineBasicBlockLabel));
+  MachineBasicBlock *AddFalthroughFrom = nullptr;
   do {
     MachineBasicBlock *MBB = nullptr;
     if (parseMBBReference(MBB))
       return true;
-    if (parseBasicBlock(*MBB))
+    if (AddFalthroughFrom) {
+      if (!AddFalthroughFrom->isSuccessor(MBB))
+        AddFalthroughFrom->addSuccessor(MBB);
+      AddFalthroughFrom->normalizeSuccProbs();
+      AddFalthroughFrom = nullptr;
+    }
+    if (parseBasicBlock(*MBB, AddFalthroughFrom))
       return true;
     // The method 'parseBasicBlock' should parse the whole block until the next
     // block or the end of file.