[PATCH] D32624: Memory intrinsic value profile optimization: Avoid divide by 0

[Teresa Johnson via Phabricator via llvm-commits]

tejohnson created this revision.

Skip memops if the total value profiled count is 0, we can't correctly
scale up the counts and there is no point anyway.


https://reviews.llvm.org/D32624

Files:
  lib/Transforms/Instrumentation/IndirectCallPromotion.cpp
  test/Transforms/PGOProfile/memop_size_opt_zero.ll


Index: test/Transforms/PGOProfile/memop_size_opt_zero.ll
===================================================================
--- /dev/null
+++ test/Transforms/PGOProfile/memop_size_opt_zero.ll
@@ -0,0 +1,19 @@
+; Test to ensure the pgo memop optimization pass doesn't try to scale
+; up a value profile with a 0 count, which would lead to divide by 0.
+; RUN: opt < %s -passes=pgo-memop-opt -pgo-memop-count-threshold=1 -S | FileCheck %s --check-prefix=MEMOP_OPT
+; RUN: opt < %s -pgo-memop-opt -pgo-memop-count-threshold=1 -S | FileCheck %s --check-prefix=MEMOP_OPT
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @foo(i8* %dst, i8* %src, i64 %conv) !prof !0 {
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %conv, i32 1, i1 false), !prof !1
+  ret void
+}
+
+; MEMOP_OPT: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %dst, i8* %src, i64 %conv, i32 1, i1 false), !prof !1
+
+!0 = !{!"function_entry_count", i64 1}
+!1 = !{!"VP", i32 1, i64 0, i64 1, i64 0, i64 2, i64 0, i64 3, i64 0, i64 9, i64 0, i64 4, i64 0, i64 5, i64 0, i64 6, i64 0, i64 7, i64 0, i64 8, i64 0}
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i32, i1)
Index: lib/Transforms/Instrumentation/IndirectCallPromotion.cpp
===================================================================
--- lib/Transforms/Instrumentation/IndirectCallPromotion.cpp
+++ lib/Transforms/Instrumentation/IndirectCallPromotion.cpp
@@ -872,6 +872,10 @@
 
   if (ActualCount < MemOPCountThreshold)
     return false;
+  // Skip if the total value profiled count is 0, in which case we can't
+  // scale up the counts properly (and there is no profitable transformation).
+  if (TotalCount == 0)
+    return false;
 
   TotalCount = ActualCount;
   if (MemOPScaleCount)


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