[PATCH] D39992: [CodeGenPrepare] Disable div bypass when working set size is huge.

[Easwaran Raman via Phabricator via llvm-commits]

eraman created this revision.

Bypass of slow divs based on operand values is currently disabled for
-Os. Do the same when profile summary is available and the working set
size of the application is huge. This is similar to how loop peeling is
guarded by hasHugeWorkingSetSize. In the div bypass case, the generated
extra code (and the extra branch) tendss to outweigh the benefits of the
bypass. This results in noticeable performance improvement on an
internal application.


https://reviews.llvm.org/D39992

Files:
  lib/CodeGen/CodeGenPrepare.cpp
  test/CodeGen/X86/bypass-slow-division-tune.ll


Index: test/CodeGen/X86/bypass-slow-division-tune.ll
===================================================================
--- test/CodeGen/X86/bypass-slow-division-tune.ll
+++ test/CodeGen/X86/bypass-slow-division-tune.ll
@@ -2,6 +2,7 @@
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu -mcpu=atom       < %s | FileCheck -check-prefixes=ATOM,CHECK %s
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu -mcpu=silvermont < %s | FileCheck -check-prefixes=REST,CHECK %s
 ; RUN: llc -mtriple=x86_64-unknown-linux-gnu -mcpu=skylake    < %s | FileCheck -check-prefixes=REST,CHECK %s
+; RUN: llc -profile-summary-huge-working-set-size-threshold=1 -mtriple=x86_64-unknown-linux-gnu -mcpu=skylake    < %s | FileCheck -check-prefixes=HUGEWS %s
 
 ; Verify that div32 is bypassed only for Atoms.
 define i32 @div32(i32 %a, i32 %b) {
@@ -36,20 +37,47 @@
 define i64 @div64_optsize(i64 %a, i64 %b) optsize {
 ; CHECK-LABEL: div64_optsize:
 ; CHECK-NOT: divl
+; CHECK: ret
+  %div = sdiv i64 %a, %b
+  ret i64 %div
+}
+
+define i64 @div64_hugews(i64 %a, i64 %b) {
+; HUGEWS-LABEL: div64_hugews:
+; HUGEWS-NOT: divl
+; HUGEWS: ret
   %div = sdiv i64 %a, %b
   ret i64 %div
 }
 
 define i32 @div32_optsize(i32 %a, i32 %b) optsize {
 ; CHECK-LABEL: div32_optsize:
 ; CHECK-NOT: divb
+; CHECK: ret
   %div = sdiv i32 %a, %b
   ret i32 %div
 }
 
 define i32 @div32_minsize(i32 %a, i32 %b) minsize {
 ; CHECK-LABEL: div32_minsize:
 ; CHECK-NOT: divb
+; CHECK: ret
   %div = sdiv i32 %a, %b
   ret i32 %div
 }
+
+!llvm.module.flags = !{!1}
+!1 = !{i32 1, !"ProfileSummary", !2}
+!2 = !{!3, !4, !5, !6, !7, !8, !9, !10}
+!3 = !{!"ProfileFormat", !"InstrProf"}
+!4 = !{!"TotalCount", i64 10000}
+!5 = !{!"MaxCount", i64 1000}
+!6 = !{!"MaxInternalCount", i64 1}
+!7 = !{!"MaxFunctionCount", i64 1000}
+!8 = !{!"NumCounts", i64 3}
+!9 = !{!"NumFunctions", i64 3}
+!10 = !{!"DetailedSummary", !11}
+!11 = !{!12, !13, !14}
+!12 = !{i32 10000, i64 1000, i32 1}
+!13 = !{i32 999000, i64 1000, i32 3}
+!14 = !{i32 999999, i64 5, i32 3}
Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -353,18 +353,19 @@
   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
   OptSize = F.optForSize();
 
+  ProfileSummaryInfo *PSI =
+      getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
   if (ProfileGuidedSectionPrefix) {
-    ProfileSummaryInfo *PSI =
-        getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
     if (PSI->isFunctionHotInCallGraph(&F))
       F.setSectionPrefix(".hot");
     else if (PSI->isFunctionColdInCallGraph(&F))
       F.setSectionPrefix(".unlikely");
   }
 
   /// This optimization identifies DIV instructions that can be
   /// profitably bypassed and carried out with a shorter, faster divide.
-  if (!OptSize && TLI && TLI->isSlowDivBypassed()) {
+  if (!OptSize && !PSI->hasHugeWorkingSetSize() && TLI &&
+      TLI->isSlowDivBypassed()) {
     const DenseMap<unsigned int, unsigned int> &BypassWidths =
        TLI->getBypassSlowDivWidths();
     BasicBlock* BB = &*F.begin();


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