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Teach SimplifyCFG that (switch (select cond, X, Y)) is better expressed as a branch.
Based on a patch by Alistair Lynn. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126647 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Frits van Bommel
parent
da834093b7
commit
f7b2a9d7df
@ -1800,6 +1800,26 @@ static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
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return true;
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}
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// SimplifySwitchOnSelect - Replaces
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// (switch (select cond, X, Y)) on constant X, Y
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// with a branch - conditional if X and Y lead to distinct BBs,
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// unconditional otherwise.
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static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
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// Check for constant integer values in the select.
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ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
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ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
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if (!TrueVal || !FalseVal)
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return false;
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// Find the relevant condition and destinations.
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Value *Condition = Select->getCondition();
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BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
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BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
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// Perform the actual simplification.
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return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
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}
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// SimplifyIndirectBrOnSelect - Replaces
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// (indirectbr (select cond, blockaddress(@fn, BlockA),
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// blockaddress(@fn, BlockB)))
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@ -2310,6 +2330,11 @@ bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
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if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
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return SimplifyCFG(BB) | true;
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Value *Cond = SI->getCondition();
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if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
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if (SimplifySwitchOnSelect(SI, Select))
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return SimplifyCFG(BB) | true;
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// If the block only contains the switch, see if we can fold the block
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// away into any preds.
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BasicBlock::iterator BBI = BB->begin();
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138
test/Transforms/SimplifyCFG/switch-on-const-select.ll
Normal file
138
test/Transforms/SimplifyCFG/switch-on-const-select.ll
Normal file
@ -0,0 +1,138 @@
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; RUN: opt < %s -simplifycfg -S | FileCheck %s
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; Test basic folding to a conditional branch.
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define i32 @foo(i64 %x, i64 %y) nounwind {
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; CHECK: @foo
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entry:
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%eq = icmp eq i64 %x, %y
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br i1 %eq, label %b, label %switch
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switch:
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%lt = icmp slt i64 %x, %y
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; CHECK: br i1 %lt, label %a, label %b
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%qux = select i1 %lt, i32 0, i32 2
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switch i32 %qux, label %bees [
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i32 0, label %a
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i32 1, label %b
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i32 2, label %b
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]
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a:
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tail call void @bees.a() nounwind
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ret i32 1
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; CHECK: b:
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; CHECK-NEXT: %retval = phi i32 [ 0, %switch ], [ 2, %entry ]
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b:
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%retval = phi i32 [0, %switch], [0, %switch], [2, %entry]
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tail call void @bees.b() nounwind
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ret i32 %retval
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; CHECK-NOT: bees:
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bees:
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tail call void @llvm.trap() nounwind
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unreachable
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}
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; Test basic folding to an unconditional branch.
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define i32 @bar(i64 %x, i64 %y) nounwind {
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; CHECK: @bar
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entry:
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; CHECK-NEXT: entry:
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; CHECK-NEXT: tail call void @bees.a() nounwind
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; CHECK-NEXT: ret i32 0
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%lt = icmp slt i64 %x, %y
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%qux = select i1 %lt, i32 0, i32 2
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switch i32 %qux, label %bees [
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i32 0, label %a
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i32 1, label %b
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i32 2, label %a
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]
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a:
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%retval = phi i32 [0, %entry], [0, %entry], [1, %b]
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tail call void @bees.a() nounwind
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ret i32 0
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b:
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tail call void @bees.b() nounwind
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br label %a
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bees:
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tail call void @llvm.trap() nounwind
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unreachable
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}
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; Test the edge case where both values from the select are the default case.
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define void @bazz(i64 %x, i64 %y) nounwind {
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; CHECK: @bazz
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entry:
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; CHECK-NEXT: entry:
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; CHECK-NEXT: tail call void @bees.b() nounwind
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; CHECK-NEXT: ret void
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%lt = icmp slt i64 %x, %y
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%qux = select i1 %lt, i32 10, i32 12
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switch i32 %qux, label %b [
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i32 0, label %a
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i32 1, label %bees
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i32 2, label %bees
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]
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a:
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tail call void @bees.a() nounwind
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ret void
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b:
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tail call void @bees.b() nounwind
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ret void
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bees:
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tail call void @llvm.trap()
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unreachable
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}
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; Test the edge case where both values from the select are equal.
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define void @quux(i64 %x, i64 %y) nounwind {
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; CHECK: @quux
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entry:
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; CHECK-NEXT: entry:
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; CHECK-NEXT: tail call void @bees.a() nounwind
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; CHECK-NEXT: ret void
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%lt = icmp slt i64 %x, %y
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%qux = select i1 %lt, i32 0, i32 0
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switch i32 %qux, label %b [
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i32 0, label %a
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i32 1, label %bees
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i32 2, label %bees
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]
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a:
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tail call void @bees.a() nounwind
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ret void
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b:
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tail call void @bees.b() nounwind
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ret void
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bees:
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tail call void @llvm.trap()
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unreachable
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}
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; A final test, for phi node munging.
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define i32 @xyzzy(i64 %x, i64 %y) {
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; CHECK: @xyzzy
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entry:
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%eq = icmp eq i64 %x, %y
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br i1 %eq, label %r, label %cont
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cont:
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; CHECK: %lt = icmp slt i64 %x, %y
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%lt = icmp slt i64 %x, %y
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; CHECK-NEXT: br i1 %lt, label %a, label %r
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%qux = select i1 %lt, i32 0, i32 2
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switch i32 %qux, label %bees [
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i32 0, label %a
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i32 1, label %r
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i32 2, label %r
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]
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r:
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%val = phi i32 [0, %entry], [1, %cont], [1, %cont]
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ret i32 %val
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a:
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ret i32 -1
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; CHECK-NOT: bees:
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bees:
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tail call void @llvm.trap()
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unreachable
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}
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declare void @llvm.trap() nounwind noreturn
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declare void @bees.a() nounwind
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declare void @bees.b() nounwind
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