forked from OSchip/llvm-project
Switch lowering: cluster adjacent fall-through cases even at -O0
It's cheap to do, and codegen is much faster if cases can be merged into clusters. llvm-svn: 236905
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@ -8012,10 +8012,12 @@ void SelectionDAGBuilder::visitSwitch(const SwitchInst &SI) {
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MachineBasicBlock *DefaultMBB = FuncInfo.MBBMap[SI.getDefaultDest()];
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if (TM.getOptLevel() != CodeGenOpt::None) {
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// Cluster adjacent cases with the same destination.
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sortAndRangeify(Clusters);
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// Cluster adjacent cases with the same destination. We do this at all
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// optimization levels because it's cheap to do and will make codegen faster
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// if there are many clusters.
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sortAndRangeify(Clusters);
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if (TM.getOptLevel() != CodeGenOpt::None) {
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// Replace an unreachable default with the most popular destination.
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// FIXME: Exploit unreachable default more aggressively.
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bool UnreachableDefault =
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@ -9,18 +9,19 @@ entry:
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i32 3, label %bb0
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i32 1, label %bb1
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i32 4, label %bb1
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i32 5, label %bb0
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i32 5, label %bb2
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]
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bb0: tail call void @g(i32 0) br label %return
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bb1: tail call void @g(i32 1) br label %return
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bb2: tail call void @g(i32 1) br label %return
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return: ret void
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; Should be lowered as straight compares in -O0 mode.
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; NOOPT-LABEL: basic
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; NOOPT: subl $3, %eax
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; NOOPT: je
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; NOOPT: subl $1, %eax
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; NOOPT: je
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; NOOPT: subl $3, %eax
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; NOOPT: je
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; NOOPT: subl $4, %eax
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; NOOPT: je
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; NOOPT: subl $5, %eax
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@ -58,6 +59,14 @@ return: ret void
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; CHECK: jae
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; CHECK: cmpl $3
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; CHECK: ja
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; We do this even at -O0, because it's cheap and makes codegen faster.
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; NOOPT-LABEL: simple_ranges
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; NOOPT: subl $4
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; NOOPT: jb
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; NOOPT: addl $-100
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; NOOPT: subl $4
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; NOOPT: jb
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}
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