[PATCH] D108204: [GVN] Execute performLoopLoadPRE ahead of PerformLoadPRE

[JinGu Kang via Phabricator via llvm-commits]

jaykang10 created this revision.
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There are cfgs which both of loop load pre and load pre can handle.

In this case, it could be better to perform loop load pre first because it can reduce the number of execution of load or it can help sccp pass propagate constant.

It fixes https://bugs.llvm.org/show_bug.cgi?id=51141


https://reviews.llvm.org/D108204

Files:
  llvm/lib/Transforms/Scalar/GVN.cpp
  llvm/test/Transforms/GVN/gvn-loop-load-pre-order.ll


Index: llvm/test/Transforms/GVN/gvn-loop-load-pre-order.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/GVN/gvn-loop-load-pre-order.ll
@@ -0,0 +1,65 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -loops -gvn -S | FileCheck -check-prefix=CHECK-PRE %s
+; RUN: opt < %s -loops -gvn -sccp -S | FileCheck -check-prefix=CHECK-SCCP %s
+
+ at b = external global i32, align 4
+
+define void @main(i1 %cond) {
+; CHECK-PRE-LABEL: @main(
+; CHECK-PRE-NEXT:  entry:
+; CHECK-PRE-NEXT:    store i32 0, i32* @b, align 4
+; CHECK-PRE-NEXT:    br label [[WHILE_BODY3:%.*]]
+; CHECK-PRE:       while.cond.loopexit.loopexit:
+; CHECK-PRE-NEXT:    ret void
+; CHECK-PRE:       while.body3:
+; CHECK-PRE-NEXT:    [[TMP0:%.*]] = phi i32 [ [[TMP1:%.*]], [[IF_END:%.*]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-PRE-NEXT:    [[TOBOOL4_NOT:%.*]] = icmp eq i32 [[TMP0]], 0
+; CHECK-PRE-NEXT:    br i1 [[TOBOOL4_NOT]], label [[IF_END]], label [[IF_THEN:%.*]]
+; CHECK-PRE:       if.then:
+; CHECK-PRE-NEXT:    tail call void @foo()
+; CHECK-PRE-NEXT:    [[DOTPRE:%.*]] = load i32, i32* @b, align 4
+; CHECK-PRE-NEXT:    br label [[IF_END]]
+; CHECK-PRE:       if.end:
+; CHECK-PRE-NEXT:    [[TMP1]] = phi i32 [ [[DOTPRE]], [[IF_THEN]] ], [ 0, [[WHILE_BODY3]] ]
+; CHECK-PRE-NEXT:    br i1 [[COND:%.*]], label [[WHILE_COND_LOOPEXIT_LOOPEXIT:%.*]], label [[WHILE_BODY3]]
+;
+; CHECK-SCCP-LABEL: @main(
+; CHECK-SCCP-NEXT:  entry:
+; CHECK-SCCP-NEXT:    store i32 0, i32* @b, align 4
+; CHECK-SCCP-NEXT:    br label [[WHILE_BODY3:%.*]]
+; CHECK-SCCP:       while.cond.loopexit.loopexit:
+; CHECK-SCCP-NEXT:    ret void
+; CHECK-SCCP:       while.body3:
+; CHECK-SCCP-NEXT:    br i1 true, label [[IF_END:%.*]], label [[IF_THEN:%.*]]
+; CHECK-SCCP:       if.then:
+; CHECK-SCCP-NEXT:    br label [[IF_END]]
+; CHECK-SCCP:       if.end:
+; CHECK-SCCP-NEXT:    br i1 [[COND:%.*]], label [[WHILE_COND_LOOPEXIT_LOOPEXIT:%.*]], label [[WHILE_BODY3]]
+;
+entry:
+  store i32 0, i32* @b
+  br label %while.body3.lr.ph
+
+while.cond.loopexit.loopexit:                     ; preds = %if.end
+  ret void
+
+while.body3.lr.ph:                                ; preds = %while.cond1.preheader
+  %0 = load i32, i32* @b, align 4
+  %1 = icmp eq i32 %0, 0
+  br label %while.body3
+
+while.body3:                                      ; preds = %if.end, %while.body3.lr.ph
+  %2 = load i32, i32* @b, align 4
+  %tobool4.not = icmp eq i32 %2, 0
+  br i1 %tobool4.not, label %if.end, label %if.then
+
+if.then:                                          ; preds = %while.body3
+  tail call void @foo()
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %while.body3
+  br i1 %cond, label %while.cond.loopexit.loopexit, label %while.body3
+}
+
+declare void @foo()
+
Index: llvm/lib/Transforms/Scalar/GVN.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/GVN.cpp
+++ llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1673,8 +1673,9 @@
   if (!isLoadInLoopPREEnabled() && LI && LI->getLoopFor(Load->getParent()))
     return Changed;
 
-  return Changed || PerformLoadPRE(Load, ValuesPerBlock, UnavailableBlocks) ||
-         performLoopLoadPRE(Load, ValuesPerBlock, UnavailableBlocks);
+  return Changed ||
+         performLoopLoadPRE(Load, ValuesPerBlock, UnavailableBlocks) ||
+         PerformLoadPRE(Load, ValuesPerBlock, UnavailableBlocks);
 }
 
 static bool impliesEquivalanceIfTrue(CmpInst* Cmp) {


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