diff options
| -rw-r--r-- | lib/Transforms/Utils/SimplifyCFG.cpp | 12 | ||||
| -rw-r--r-- | test/Transforms/SimplifyCFG/switch-dead-default.ll | 100 |
2 files changed, 105 insertions, 7 deletions
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index e00a96161cd..b02d2923b8e 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -3423,11 +3423,17 @@ static bool EliminateDeadSwitchCases(SwitchInst *SI, AssumptionCache *AC, } // If we can prove that the cases must cover all possible values, the - // default destination becomes dead and we can remove it. + // default destination becomes dead and we can remove it. If we know some + // of the bits in the value, we can use that to more precisely compute the + // number of possible unique case values. bool HasDefault = !isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg()); - if (HasDefault && Bits < 64 /* avoid overflow */ && - SI->getNumCases() == (1ULL << Bits)) { + const unsigned NumUnknownBits = Bits - + (KnownZero.Or(KnownOne)).countPopulation(); + assert(0 <= NumUnknownBits && NumUnknownBits <= Bits); + if (HasDefault && DeadCases.empty() && + NumUnknownBits < 64 /* avoid overflow */ && + SI->getNumCases() == (1ULL << NumUnknownBits)) { DEBUG(dbgs() << "SimplifyCFG: switch default is dead.\n"); BasicBlock *NewDefault = SplitBlockPredecessors(SI->getDefaultDest(), SI->getParent(), ""); diff --git a/test/Transforms/SimplifyCFG/switch-dead-default.ll b/test/Transforms/SimplifyCFG/switch-dead-default.ll index b54ea881d8b..e5c2ef65b31 100644 --- a/test/Transforms/SimplifyCFG/switch-dead-default.ll +++ b/test/Transforms/SimplifyCFG/switch-dead-default.ll @@ -2,7 +2,7 @@ declare void @foo(i32) define void @test(i1 %a) { -; CHECK-LABEL @test +; CHECK-LABEL: @test ; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false switch i1 %a, label %default [i1 1, label %true i1 0, label %false] @@ -18,7 +18,7 @@ default: } define void @test2(i2 %a) { -; CHECK-LABEL @test2 +; CHECK-LABEL: @test2 switch i2 %a, label %default [i2 0, label %case0 i2 1, label %case1 i2 2, label %case2 @@ -45,7 +45,7 @@ default: ; This one is a negative test - we know the value of the default, ; but that's about it define void @test3(i2 %a) { -; CHECK-LABEL @test3 +; CHECK-LABEL: @test3 switch i2 %a, label %default [i2 0, label %case0 i2 1, label %case1 i2 2, label %case2] @@ -69,7 +69,7 @@ default: ; Negative test - check for possible overflow when computing ; number of possible cases. define void @test4(i128 %a) { -; CHECK-LABEL @test4 +; CHECK-LABEL: @test4 switch i128 %a, label %default [i128 0, label %case0 i128 1, label %case1] @@ -85,3 +85,95 @@ default: call void @foo(i32 0) ret void } + +; All but one bit known zero +define void @test5(i8 %a) { +; CHECK-LABEL: @test5 +; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false + %cmp = icmp ult i8 %a, 2 + call void @llvm.assume(i1 %cmp) + switch i8 %a, label %default [i8 1, label %true + i8 0, label %false] +true: + call void @foo(i32 1) + ret void +false: + call void @foo(i32 3) + ret void +default: + call void @foo(i32 2) + ret void +} + +;; All but one bit known one +define void @test6(i8 %a) { +; CHECK-LABEL: @test6 +; CHECK: @llvm.assume +; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false + %and = and i8 %a, 254 + %cmp = icmp eq i8 %and, 254 + call void @llvm.assume(i1 %cmp) + switch i8 %a, label %default [i8 255, label %true + i8 254, label %false] +true: + call void @foo(i32 1) + ret void +false: + call void @foo(i32 3) + ret void +default: + call void @foo(i32 2) + ret void +} + +; Check that we can eliminate both dead cases and dead defaults +; within a single run of simplify-cfg +define void @test7(i8 %a) { +; CHECK-LABEL: @test7 +; CHECK: @llvm.assume +; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false + %and = and i8 %a, 254 + %cmp = icmp eq i8 %and, 254 + call void @llvm.assume(i1 %cmp) + switch i8 %a, label %default [i8 255, label %true + i8 254, label %false + i8 0, label %also_dead] +true: + call void @foo(i32 1) + ret void +false: + call void @foo(i32 3) + ret void +also_dead: + call void @foo(i32 5) + ret void +default: + call void @foo(i32 2) + ret void +} + +;; All but one bit known undef +;; Note: This is currently testing an optimization which doesn't trigger. The +;; case this is protecting against is that a bit could be assumed both zero +;; *or* one given we know it's undef. ValueTracking doesn't do this today, +;; but it doesn't hurt to confirm. +define void @test8(i8 %a) { +; CHECK-LABEL: @test8( +; CHECK: switch i8 + %and = and i8 %a, 254 + %cmp = icmp eq i8 %and, undef + call void @llvm.assume(i1 %cmp) + switch i8 %a, label %default [i8 255, label %true + i8 254, label %false] +true: + call void @foo(i32 1) + ret void +false: + call void @foo(i32 3) + ret void +default: + call void @foo(i32 2) + ret void +} + +declare void @llvm.assume(i1) |