[PATCH] D24788: Change the basic block weight calculation algorithm to use max instead of voting.

[Dehao Chen via llvm-commits]

danielcdh created this revision.
danielcdh added a reviewer: dnovillo.
danielcdh added a subscriber: llvm-commits.

Now that we have more precise debug info, we should change back to use maximum to get basic block weight.

https://reviews.llvm.org/D24788

Files:
  lib/Transforms/IPO/SampleProfile.cpp
  test/Transforms/SampleProfile/calls.ll
  test/Transforms/SampleProfile/fnptr.ll

Index: test/Transforms/SampleProfile/fnptr.ll
===================================================================
--- test/Transforms/SampleProfile/fnptr.ll
+++ test/Transforms/SampleProfile/fnptr.ll
@@ -8,10 +8,10 @@
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/fnptr.prof | opt -analyze -branch-prob | FileCheck %s
 ; RUN: opt < %s -passes=sample-profile -sample-profile-file=%S/Inputs/fnptr.binprof | opt -analyze -branch-prob | FileCheck %s
 
-; CHECK:   edge for.body3 -> if.then probability is 0x1a56a56a / 0x80000000 = 20.58%
-; CHECK:   edge for.body3 -> if.else probability is 0x65a95a96 / 0x80000000 = 79.42%
-; CHECK:   edge for.inc -> for.inc12 probability is 0x000fdc50 / 0x80000000 = 0.05%
-; CHECK:   edge for.inc -> for.body3 probability is 0x7ff023b0 / 0x80000000 = 99.95%
+; CHECK:   edge for.body3 -> if.then probability is 0x19f584f3 / 0x80000000 = 20.28%
+; CHECK:   edge for.body3 -> if.else probability is 0x660a7b0d / 0x80000000 = 79.72%
+; CHECK:   edge for.inc -> for.inc12 probability is 0x000f92fb / 0x80000000 = 0.05%
+; CHECK:   edge for.inc -> for.body3 probability is 0x7ff06d05 / 0x80000000 = 99.95%
 ; CHECK:   edge for.inc12 -> for.end14 probability is 0x04000000 / 0x80000000 = 3.12%
 ; CHECK:   edge for.inc12 -> for.cond1.preheader probability is 0x7c000000 / 0x80000000 = 96.88%
 
Index: test/Transforms/SampleProfile/calls.ll
===================================================================
--- test/Transforms/SampleProfile/calls.ll
+++ test/Transforms/SampleProfile/calls.ll
@@ -48,8 +48,8 @@
   store i32 %inc, i32* %i, align 4, !dbg !14
   %cmp = icmp slt i32 %0, 400000000, !dbg !14
   br i1 %cmp, label %while.body, label %while.end, !dbg !14
-; CHECK: edge while.cond -> while.body probability is 0x7ffa4e20 / 0x80000000 = 99.98% [HOT edge]
-; CHECK: edge while.cond -> while.end probability is 0x0005b1e0 / 0x80000000 = 0.02%
+; CHECK: edge while.cond -> while.body probability is 0x7d9eb367 / 0x80000000 = 98.14% [HOT edge]
+; CHECK: edge while.cond -> while.end probability is 0x02614c99 / 0x80000000 = 1.86%
 
 while.body:                                       ; preds = %while.cond
   %1 = load i32, i32* %i, align 4, !dbg !16
@@ -59,8 +59,8 @@
 ; both branches out of while.body had the same weight. In reality,
 ; the edge while.body->if.then is taken most of the time.
 ;
-; CHECK: edge while.body -> if.else probability is 0x0005b1e0 / 0x80000000 = 0.02%
-; CHECK: edge while.body -> if.then probability is 0x7ffa4e20 / 0x80000000 = 99.98% [HOT edge]
+; CHECK: edge while.body -> if.else probability is 0x00059704 / 0x80000000 = 0.02%
+; CHECK: edge while.body -> if.then probability is 0x7ffa68fc / 0x80000000 = 99.98% [HOT edge]
 
 
 if.then:                                          ; preds = %while.body
Index: lib/Transforms/IPO/SampleProfile.cpp
===================================================================
--- lib/Transforms/IPO/SampleProfile.cpp
+++ lib/Transforms/IPO/SampleProfile.cpp
@@ -513,24 +513,16 @@
 /// \returns the weight for \p BB.
 ErrorOr<uint64_t>
 SampleProfileLoader::getBlockWeight(const BasicBlock *BB) const {
-  DenseMap<uint64_t, uint64_t> CM;
+  uint64_t Max = 0;
+  bool HasWeight = false;
   for (auto &I : BB->getInstList()) {
     const ErrorOr<uint64_t> &R = getInstWeight(I);
-    if (R)
-      CM[R.get()]++;
-  }
-  if (CM.size() == 0)
-    return std::error_code();
-  uint64_t W = 0, C = 0;
-  for (const auto &C_W : CM) {
-    if (C_W.second == W) {
-      C = std::max(C, C_W.first);
-    } else if (C_W.second > W) {
-      C = C_W.first;
-      W = C_W.second;
+    if (R) {
+      Max = std::max(Max, R.get());
+      HasWeight = true;
     }
   }
-  return C;
+  return HasWeight ? ErrorOr<uint64_t>(Max) : std::error_code();
 }
 
 /// \brief Compute and store the weights of every basic block.


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