[llvm] r349217 - [NewGVN] Update use counts for SSA copies when replacing them by their operands.
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 14 16:32:38 PST 2018
Author: fhahn
Date: Fri Dec 14 16:32:38 2018
New Revision: 349217
URL: http://llvm.org/viewvc/llvm-project?rev=349217&view=rev
Log:
[NewGVN] Update use counts for SSA copies when replacing them by their operands.
The current code relies on LeaderUseCount to determine if we can remove
an SSA copy, but in that the LeaderUseCount does not refer to the SSA
copy. If a SSA copy is a dominating leader, we use the operand as dominating
leader instead. This means we removed a user of a ssa copy and we should
decrement its use count, so we can remove the ssa copy once it becomes dead.
Fixes PR38804.
Reviewers: efriedma, davide
Reviewed By: davide
Differential Revision: https://reviews.llvm.org/D51595
Added:
llvm/trunk/test/Transforms/NewGVN/eliminate-ssacopy.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp?rev=349217&r1=349216&r2=349217&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp Fri Dec 14 16:32:38 2018
@@ -4093,10 +4093,13 @@ bool NewGVN::eliminateInstructions(Funct
// It's about to be alive again.
if (LeaderUseCount == 0 && isa<Instruction>(DominatingLeader))
ProbablyDead.erase(cast<Instruction>(DominatingLeader));
- // Copy instructions, however, are still dead because we use their
- // operand as the leader.
- if (LeaderUseCount == 0 && isSSACopy)
- ProbablyDead.insert(II);
+ // For copy instructions, we use their operand as a leader,
+ // which means we remove a user of the copy and it may become dead.
+ if (isSSACopy) {
+ unsigned &IIUseCount = UseCounts[II];
+ if (--IIUseCount == 0)
+ ProbablyDead.insert(II);
+ }
++LeaderUseCount;
AnythingReplaced = true;
}
Added: llvm/trunk/test/Transforms/NewGVN/eliminate-ssacopy.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NewGVN/eliminate-ssacopy.ll?rev=349217&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/NewGVN/eliminate-ssacopy.ll (added)
+++ llvm/trunk/test/Transforms/NewGVN/eliminate-ssacopy.ll Fri Dec 14 16:32:38 2018
@@ -0,0 +1,81 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -newgvn -S < %s | FileCheck %s
+
+; Make sure the created ssa copies are cleaned up. See PR38804.
+
+; CHECK-NOT: ssa_copy
+
+ at b = external dso_local local_unnamed_addr global i32, align 4
+ at a = external dso_local local_unnamed_addr global i8, align 1
+ at f = external dso_local local_unnamed_addr global i16, align 2
+
+define void @g() {
+; CHECK-LABEL: @g(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: br i1 undef, label [[FOR_COND1THREAD_PRE_SPLIT:%.*]], label [[FOR_COND_PREHEADER:%.*]]
+; CHECK: for.cond.preheader:
+; CHECK-NEXT: unreachable
+; CHECK: for.cond1thread-pre-split:
+; CHECK-NEXT: br label [[FOR_END4_SPLIT:%.*]]
+; CHECK: for.end4.split:
+; CHECK-NEXT: br i1 true, label [[FOR_COND6_PREHEADER:%.*]], label [[IF_END11:%.*]]
+; CHECK: for.cond6.preheader:
+; CHECK-NEXT: br i1 undef, label [[FOR_COND6_PREHEADER3:%.*]], label [[IF_END11_LOOPEXIT:%.*]]
+; CHECK: for.cond6.preheader3:
+; CHECK-NEXT: br label [[IF_END11_LOOPEXIT]]
+; CHECK: if.end11.loopexit:
+; CHECK-NEXT: [[STOREMERGE_LCSSA:%.*]] = phi i32 [ 0, [[FOR_COND6_PREHEADER]] ], [ 1, [[FOR_COND6_PREHEADER3]] ]
+; CHECK-NEXT: store i32 [[STOREMERGE_LCSSA]], i32* @b, align 4
+; CHECK-NEXT: br label [[IF_END11]]
+; CHECK: if.end11:
+; CHECK-NEXT: [[TMP0:%.*]] = load i32, i32* @b, align 4
+; CHECK-NEXT: [[TMP1:%.*]] = load i8, i8* @a, align 1
+; CHECK-NEXT: [[CONV:%.*]] = sext i8 [[TMP1]] to i32
+; CHECK-NEXT: [[CMP12:%.*]] = icmp eq i32 [[TMP0]], [[CONV]]
+; CHECK-NEXT: br i1 [[CMP12]], label [[IF_THEN14:%.*]], label [[IF_END16:%.*]]
+; CHECK: if.then14:
+; CHECK-NEXT: [[CONV15:%.*]] = trunc i32 [[TMP0]] to i16
+; CHECK-NEXT: store i16 [[CONV15]], i16* @f, align 2
+; CHECK-NEXT: unreachable
+; CHECK: if.end16:
+; CHECK-NEXT: ret void
+;
+entry:
+ %tobool = icmp eq i32 undef, 0
+ br i1 %tobool, label %for.cond1thread-pre-split, label %for.cond.preheader
+
+for.cond.preheader: ; preds = %entry
+ unreachable
+
+for.cond1thread-pre-split: ; preds = %entry
+ br label %for.end4.split
+
+for.end4.split: ; preds = %for.cond1thread-pre-split
+ br i1 %tobool, label %for.cond6.preheader, label %if.end11
+
+for.cond6.preheader: ; preds = %for.end4.split
+ br i1 undef, label %for.cond6.preheader3, label %if.end11.loopexit
+
+for.cond6.preheader3: ; preds = %for.cond6.preheader
+ br label %if.end11.loopexit
+
+if.end11.loopexit: ; preds = %for.cond6.preheader3, %for.cond6.preheader
+ %storemerge.lcssa = phi i32 [ 0, %for.cond6.preheader ], [ 1, %for.cond6.preheader3 ]
+ store i32 %storemerge.lcssa, i32* @b, align 4
+ br label %if.end11
+
+if.end11: ; preds = %if.end11.loopexit, %for.end4.split
+ %0 = load i32, i32* @b, align 4
+ %1 = load i8, i8* @a, align 1
+ %conv = sext i8 %1 to i32
+ %cmp12 = icmp eq i32 %0, %conv
+ br i1 %cmp12, label %if.then14, label %if.end16
+
+if.then14: ; preds = %if.end11
+ %conv15 = trunc i32 %0 to i16
+ store i16 %conv15, i16* @f, align 2
+ unreachable
+
+if.end16: ; preds = %if.end11
+ ret void
+}
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