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to have single return block (at least getting there) for optimizations. This is general goodness but it would prevent some tailcall optimizations. One specific case is code like this: int f1(void); int f2(void); int f3(void); int f4(void); int f5(void); int f6(void); int foo(int x) { switch(x) { case 1: return f1(); case 2: return f2(); case 3: return f3(); case 4: return f4(); case 5: return f5(); case 6: return f6(); } } => LBB0_2: ## %sw.bb callq _f1 popq %rbp ret LBB0_3: ## %sw.bb1 callq _f2 popq %rbp ret LBB0_4: ## %sw.bb3 callq _f3 popq %rbp ret This patch teaches codegenprep to duplicate returns when the return value is a phi and where the phi operands are produced by tail calls followed by an unconditional branch: sw.bb7: ; preds = %entry %call8 = tail call i32 @f5() nounwind br label %return sw.bb9: ; preds = %entry %call10 = tail call i32 @f6() nounwind br label %return return: %retval.0 = phi i32 [ %call10, %sw.bb9 ], [ %call8, %sw.bb7 ], ... [ 0, %entry ] ret i32 %retval.0 This allows codegen to generate better code like this: LBB0_2: ## %sw.bb jmp _f1 ## TAILCALL LBB0_3: ## %sw.bb1 jmp _f2 ## TAILCALL LBB0_4: ## %sw.bb3 jmp _f3 ## TAILCALL rdar://9147433 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127953 91177308-0d34-0410-b5e6-96231b3b80d8 |
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.. | ||
Mangler.h | ||
SubtargetFeature.h | ||
Target.td | ||
TargetAsmBackend.h | ||
TargetAsmInfo.h | ||
TargetAsmLexer.h | ||
TargetAsmParser.h | ||
TargetCallingConv.h | ||
TargetCallingConv.td | ||
TargetData.h | ||
TargetELFWriterInfo.h | ||
TargetFrameLowering.h | ||
TargetInstrDesc.h | ||
TargetInstrInfo.h | ||
TargetInstrItineraries.h | ||
TargetIntrinsicInfo.h | ||
TargetJITInfo.h | ||
TargetLibraryInfo.h | ||
TargetLowering.h | ||
TargetLoweringObjectFile.h | ||
TargetMachine.h | ||
TargetOpcodes.h | ||
TargetOptions.h | ||
TargetRegisterInfo.h | ||
TargetRegistry.h | ||
TargetSchedule.td | ||
TargetSelect.h | ||
TargetSelectionDAG.td | ||
TargetSelectionDAGInfo.h | ||
TargetSubtarget.h |