[DSE,MemorySSA] Add an early check for read clobbers to traversal.
Depending on the benchmark, this early exit can save a substantial amount of compile-time: http://llvm-compile-time-tracker.com/compare.php?from=505f2d817aa8e07ba98e5fd4a8f6ff0666f89df1&to=eb4e441147f9b4b7a5fcbbc57428cadbe9e01f10&stat=instructions
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@ -1901,6 +1901,18 @@ struct DSEState {
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return None;
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}
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// Quick check if there are direct uses that are read-clobbers.
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if (any_of(Current->uses(), [this, &DefLoc, StartAccess](Use &U) {
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if (auto *UseOrDef = dyn_cast<MemoryUseOrDef>(U.getUser()))
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return !MSSA.dominates(StartAccess, UseOrDef) &&
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isReadClobber(DefLoc, UseOrDef->getMemoryInst());
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return false;
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})) {
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Cache.KnownReads.insert(Current);
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LLVM_DEBUG(dbgs() << " ... found a read clobber\n");
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return None;
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}
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// If Current cannot be analyzed or is not removable, check the next
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// candidate.
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if (!hasAnalyzableMemoryWrite(CurrentI, TLI) || !isRemovable(CurrentI)) {
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@ -0,0 +1,58 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt -dse -enable-dse-memoryssa -S %s | FileCheck %s
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declare i1 @cond() readnone
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define i32 @test() {
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; CHECK-LABEL: @test(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[M0:%.*]] = alloca [4 x i32], align 16
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; CHECK-NEXT: br label [[LOOP_1:%.*]]
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; CHECK: loop.1:
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; CHECK-NEXT: br label [[LOOP_2:%.*]]
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; CHECK: loop.2:
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; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 0, [[LOOP_1]] ], [ [[IV_NEXT:%.*]], [[LOOP_2]] ]
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; CHECK-NEXT: [[PTR_1:%.*]] = getelementptr inbounds [4 x i32], [4 x i32]* [[M0]], i64 3, i64 [[IV]]
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; CHECK-NEXT: [[PTR_2:%.*]] = getelementptr inbounds [4 x i32], [4 x i32]* [[M0]], i64 0, i64 [[IV]]
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; CHECK-NEXT: store i32 20, i32* [[PTR_2]], align 4
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; CHECK-NEXT: store i32 30, i32* [[PTR_1]], align 4
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; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
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; CHECK-NEXT: [[C_3:%.*]] = call i1 @cond()
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; CHECK-NEXT: br i1 [[C_3]], label [[LOOP_1_LATCH:%.*]], label [[LOOP_2]]
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; CHECK: loop.1.latch:
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; CHECK-NEXT: [[C_2:%.*]] = call i1 @cond()
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; CHECK-NEXT: br i1 [[C_2]], label [[EXIT:%.*]], label [[LOOP_1]]
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; CHECK: exit:
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; CHECK-NEXT: [[PTR_3:%.*]] = getelementptr inbounds [4 x i32], [4 x i32]* [[M0]], i64 0, i64 1
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; CHECK-NEXT: [[LV:%.*]] = load i32, i32* [[PTR_3]], align 16
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; CHECK-NEXT: ret i32 [[LV]]
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;
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entry:
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%M0 = alloca [4 x i32], align 16
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br label %loop.1
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loop.1:
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br label %loop.2
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loop.2:
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%iv = phi i64 [ 0, %loop.1 ], [ %iv.next, %loop.2 ]
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%ptr.1 = getelementptr inbounds [4 x i32], [4 x i32]* %M0, i64 3, i64 %iv
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store i32 10, i32* %ptr.1, align 4
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%ptr.2 = getelementptr inbounds [4 x i32], [4 x i32]* %M0, i64 0, i64 %iv
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store i32 20, i32* %ptr.2, align 4
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store i32 30, i32* %ptr.1, align 4
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%iv.next = add nuw nsw i64 %iv, 1
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%c.3 = call i1 @cond()
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br i1 %c.3, label %loop.1.latch, label %loop.2
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loop.1.latch:
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%c.2 = call i1 @cond()
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br i1 %c.2, label %exit, label %loop.1
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exit:
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%ptr.3 = getelementptr inbounds [4 x i32], [4 x i32]* %M0, i64 0, i64 1
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%lv = load i32, i32* %ptr.3, align 16
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ret i32 %lv
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}
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