Teach the BranchProbabilityInfo pass to print its results, and use that

to bring it under direct test instead of merely indirectly testing it in
the BlockFrequencyInfo pass.

The next step is to start adding tests for the various heuristics
employed, and to start fixing those heuristics once they're under test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142778 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/BranchProbabilityInfo.h

@@ -37,6 +37,9 @@ class BranchProbabilityInfo : public FunctionPass {
 
   DenseMap<Edge, uint32_t> Weights;
 
+  /// \brief Track the last function we run over for printing.
+  Function *LastF;
+
   // Get sum of the block successors' weights.
   uint32_t getSumForBlock(const BasicBlock *BB) const;
 
@@ -48,8 +51,8 @@ public:
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const;
-
   bool runOnFunction(Function &F);
+  void print(raw_ostream &OS, const Module *M = 0) const;
 
   // Returned value is between 1 and UINT32_MAX. Look at
   // BranchProbabilityInfo.cpp for details.
@@ -74,8 +77,8 @@ public:
   // Print value between 0 (0% probability) and 1 (100% probability),
   // however the value is never equal to 0, and can be 1 only iff SRC block
   // has only one successor.
-  raw_ostream &printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
-                                    BasicBlock *Dst) const;
+  raw_ostream &printEdgeProbability(raw_ostream &OS, const BasicBlock *Src,
+                                    const BasicBlock *Dst) const;
 };
 
 }

lib/Analysis/BranchProbabilityInfo.cpp

@@ -12,11 +12,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Constants.h"
+#include "llvm/Function.h"
 #include "llvm/Instructions.h"
 #include "llvm/LLVMContext.h"
 #include "llvm/Metadata.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Support/CFG.h"
 #include "llvm/Support/Debug.h"
 
 using namespace llvm;
@@ -453,11 +455,26 @@ void BranchProbabilityInfo::getAnalysisUsage(AnalysisUsage &AU) const {
 }
 
 bool BranchProbabilityInfo::runOnFunction(Function &F) {
+  LastF = &F; // Store the last function we ran on for printing.
   LoopInfo &LI = getAnalysis<LoopInfo>();
   BranchProbabilityAnalysis BPA(this, &LI);
   return BPA.runOnFunction(F);
 }
 
+void BranchProbabilityInfo::print(raw_ostream &OS, const Module *) const {
+  OS << "---- Branch Probabilities ----\n";
+  // We print the probabilities from the last function the analysis ran over,
+  // or the function it is currently running over.
+  assert(LastF && "Cannot print prior to running over a function");
+  for (Function::const_iterator BI = LastF->begin(), BE = LastF->end();
+       BI != BE; ++BI) {
+    for (succ_const_iterator SI = succ_begin(BI), SE = succ_end(BI);
+         SI != SE; ++SI) {
+      printEdgeProbability(OS << "  ", BI, *SI);
+    }
+  }
+}
+
 uint32_t BranchProbabilityInfo::getSumForBlock(const BasicBlock *BB) const {
   uint32_t Sum = 0;
 
@@ -537,8 +554,9 @@ getEdgeProbability(const BasicBlock *Src, const BasicBlock *Dst) const {
 }
 
 raw_ostream &
-BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
-                                            BasicBlock *Dst) const {
+BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS,
+                                            const BasicBlock *Src,
+                                            const BasicBlock *Dst) const {
 
   const BranchProbability Prob = getEdgeProbability(Src, Dst);
   OS << "edge " << Src->getNameStr() << " -> " << Dst->getNameStr()

test/Analysis/BranchProbabilityInfo/basic.ll

@@ -0,0 +1,90 @@
+; RUN: opt < %s -analyze -branch-prob | FileCheck %s
+
+define i32 @test1(i32 %i, i32* %a) {
+; CHECK: Printing analysis {{.*}} for function 'test1'
+entry:
+  br label %body
+; CHECK: edge entry -> body probability is 16 / 16 = 100%
+
+body:
+  %iv = phi i32 [ 0, %entry ], [ %next, %body ]
+  %base = phi i32 [ 0, %entry ], [ %sum, %body ]
+  %arrayidx = getelementptr inbounds i32* %a, i32 %iv
+  %0 = load i32* %arrayidx
+  %sum = add nsw i32 %0, %base
+  %next = add i32 %iv, 1
+  %exitcond = icmp eq i32 %next, %i
+  br i1 %exitcond, label %exit, label %body
+; CHECK: edge body -> exit probability is 4 / 128
+; CHECK: edge body -> body probability is 124 / 128
+
+exit:
+  ret i32 %sum
+}
+
+define i32 @test2(i32 %i, i32 %a, i32 %b) {
+; CHECK: Printing analysis {{.*}} for function 'test2'
+entry:
+  %cond = icmp ult i32 %i, 42
+  br i1 %cond, label %then, label %else, !prof !0
+; CHECK: edge entry -> then probability is 64 / 68
+; CHECK: edge entry -> else probability is 4 / 68
+
+then:
+  br label %exit
+; CHECK: edge then -> exit probability is 16 / 16 = 100%
+
+else:
+  br label %exit
+; CHECK: edge else -> exit probability is 16 / 16 = 100%
+
+exit:
+  %result = phi i32 [ %a, %then ], [ %b, %else ]
+  ret i32 %result
+}
+
+!0 = metadata !{metadata !"branch_weights", i32 64, i32 4}
+
+define i32 @test3(i32 %i, i32 %a, i32 %b, i32 %c, i32 %d, i32 %e) {
+; CHECK: Printing analysis {{.*}} for function 'test3'
+entry:
+  switch i32 %i, label %case_a [ i32 1, label %case_b
+                                 i32 2, label %case_c
+                                 i32 3, label %case_d
+                                 i32 4, label %case_e ], !prof !1
+; CHECK: edge entry -> case_a probability is 4 / 80
+; CHECK: edge entry -> case_b probability is 4 / 80
+; CHECK: edge entry -> case_c probability is 64 / 80
+; CHECK: edge entry -> case_d probability is 4 / 80
+; CHECK: edge entry -> case_e probability is 4 / 80
+
+case_a:
+  br label %exit
+; CHECK: edge case_a -> exit probability is 16 / 16 = 100%
+
+case_b:
+  br label %exit
+; CHECK: edge case_b -> exit probability is 16 / 16 = 100%
+
+case_c:
+  br label %exit
+; CHECK: edge case_c -> exit probability is 16 / 16 = 100%
+
+case_d:
+  br label %exit
+; CHECK: edge case_d -> exit probability is 16 / 16 = 100%
+
+case_e:
+  br label %exit
+; CHECK: edge case_e -> exit probability is 16 / 16 = 100%
+
+exit:
+  %result = phi i32 [ %a, %case_a ],
+                    [ %b, %case_b ],
+                    [ %c, %case_c ],
+                    [ %d, %case_d ],
+                    [ %e, %case_e ]
+  ret i32 %result
+}
+
+!1 = metadata !{metadata !"branch_weights", i32 4, i32 4, i32 64, i32 4, i32 4}

test/Analysis/BranchProbabilityInfo/dg.exp

@@ -0,0 +1,3 @@
+load_lib llvm.exp
+
+RunLLVMTests [lsort [glob -nocomplain $srcdir/$subdir/*.{ll,c,cpp}]]