diff options
| -rw-r--r-- | llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 21 | ||||
| -rw-r--r-- | llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll | 40 |
2 files changed, 55 insertions, 6 deletions
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp index ab45c1d21a5..50ebdb77158 100644 --- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp @@ -3486,6 +3486,21 @@ GetCaseResults(SwitchInst *SI, continue; } else if (Constant *C = ConstantFold(I, ConstantPool, DL)) { // Instruction is side-effect free and constant. + + // If the instruction has uses outside this block or a phi node slot for + // the block, it is not safe to bypass the instruction since it would then + // no longer dominate all its uses. + for (auto &Use : I->uses()) { + User *User = Use.getUser(); + if (Instruction *I = dyn_cast<Instruction>(User)) + if (I->getParent() == CaseDest) + continue; + if (PHINode *Phi = dyn_cast<PHINode>(User)) + if (Phi->getIncomingBlock(Use) == CaseDest) + continue; + return false; + } + ConstantPool.insert(std::make_pair(I, C)); } else { break; @@ -3511,12 +3526,6 @@ GetCaseResults(SwitchInst *SI, if (!ConstVal) return false; - // Note: If the constant comes from constant-propagating the case value - // through the CaseDest basic block, it will be safe to remove the - // instructions in that block. They cannot be used (except in the phi nodes - // we visit) outside CaseDest, because that block does not dominate its - // successor. If it did, we would not be in this phi node. - // Be conservative about which kinds of constants we support. if (!ValidLookupTableConstant(ConstVal)) return false; diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll index 95c9cc539d2..22f18cd4d43 100644 --- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll +++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll @@ -1204,3 +1204,43 @@ return: ; CHECK-NEXT: [[R:%.+]] = select i1 %cmp ; CHECK-NEXT: ret i32 [[R]] } + +define void @pr20210(i8 %x, i1 %y) { +; %z has uses outside of its BB or the phi it feeds into, +; so doing a table lookup and jumping directly to while.cond would +; cause %z to cease dominating all its uses. + +entry: + br i1 %y, label %sw, label %intermediate + +sw: + switch i8 %x, label %end [ + i8 7, label %intermediate + i8 3, label %intermediate + i8 2, label %intermediate + i8 1, label %intermediate + i8 0, label %intermediate + ] + +intermediate: + %z = zext i8 %x to i32 + br label %while.cond + +while.cond: + %i = phi i32 [ %z, %intermediate ], [ %j, %while.body ] + %b = icmp ne i32 %i, 7 + br i1 %b, label %while.body, label %while.end + +while.body: + %j = add i32 %i, 1 + br label %while.cond + +while.end: + call void @exit(i32 %z) + unreachable + +end: + ret void +; CHECK-LABEL: @pr20210 +; CHECK: switch i8 %x +} |
