[PATCH] D75400: [LICM] Allow freeze to hoist out of a loop

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune updated this revision to Diff 247440.
aqjune added a comment.

Update


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75400/new/

https://reviews.llvm.org/D75400

Files:
  llvm/lib/Transforms/Scalar/LICM.cpp
  llvm/test/Transforms/LICM/freeze.ll


Index: llvm/test/Transforms/LICM/freeze.ll
===================================================================
--- llvm/test/Transforms/LICM/freeze.ll
+++ llvm/test/Transforms/LICM/freeze.ll
@@ -1,8 +1,8 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -licm -S < %s | FileCheck %s
 
-define void @licm(i1 %a) {
-; CHECK-LABEL: @licm(
+define void @hoist(i1 %a) {
+; CHECK-LABEL: @hoist(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[B:%.*]] = freeze i1 [[A:%.*]]
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
@@ -18,4 +18,26 @@
   br label %loop
 }
 
+define i1 @sink(i1 %a) {
+; CHECK-LABEL: @sink(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[C:%.*]] = call i1 @cond()
+; CHECK-NEXT:    br i1 [[C]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[FR_LE:%.*]] = freeze i1 [[A:%.*]]
+; CHECK-NEXT:    ret i1 [[FR_LE]]
+;
+entry:
+  br label %loop
+loop:
+  %fr = freeze i1 %a
+  %c = call i1 @cond()
+  br i1 %c, label %loop, label %exit
+exit:
+  ret i1 %fr
+}
+
+declare i1 @cond()
 declare void @use(i1)
Index: llvm/lib/Transforms/Scalar/LICM.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LICM.cpp
+++ llvm/lib/Transforms/Scalar/LICM.cpp
@@ -1231,10 +1231,6 @@
       return MSSA->isLiveOnEntryDef(Source) ||
              !CurLoop->contains(Source->getBlock());
     }
-  } else if (isa<FreezeInst>(&I)) {
-    // Freeze instruction cannot be sunk into a loop because it may yield a
-    // different value for each iteration after sinking.
-    return !Flags->IsSink;
   }
 
   assert(!I.mayReadOrWriteMemory() && "unhandled aliasing");
@@ -1949,7 +1945,7 @@
         // Note that proving a load safe to speculate requires proving
         // sufficient alignment at the target location.  Proving it guaranteed
         // to execute does as well.  Thus we can increase our guaranteed
-        // alignment as well.
+        // alignment as well. 
         if (!DereferenceableInPH || (InstAlignment > Alignment))
           if (isSafeToExecuteUnconditionally(*Load, DT, CurLoop, SafetyInfo,
                                              ORE, Preheader->getTerminator())) {


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