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Teach DAE to look for functions whose arguments are unused, and change all callers to pass in an undefvalue instead.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123596 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -39,7 +39,8 @@ using namespace llvm;
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STATISTIC(NumArgumentsEliminated, "Number of unread args removed");
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STATISTIC(NumRetValsEliminated , "Number of unused return values removed");
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STATISTIC(NumArgumentsReplacedWithUndef,
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"Number of unread args replaced with undef");
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namespace {
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/// DAE - The dead argument elimination pass.
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///
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@ -148,6 +149,7 @@ namespace {
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void PropagateLiveness(const RetOrArg &RA);
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bool RemoveDeadStuffFromFunction(Function *F);
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bool DeleteDeadVarargs(Function &Fn);
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bool RemoveDeadArgumentsFromCallers(Function &Fn);
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};
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}
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@ -287,6 +289,55 @@ bool DAE::DeleteDeadVarargs(Function &Fn) {
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return true;
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}
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/// RemoveDeadArgumentsFromCallers - Checks if the given function has any
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/// arguments that are unused, and changes the caller parameters to be undefined
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/// instead.
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bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
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{
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if (Fn.isDeclaration())
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return false;
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// Functions with local linkage should already have been handled.
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if (Fn.hasLocalLinkage())
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return false;
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if (Fn.use_empty())
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return false;
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llvm::SmallVector<unsigned, 8> UnusedArgs;
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for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
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I != E; ++I) {
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Argument *Arg = I;
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if (Arg->use_empty() && !Arg->hasByValAttr())
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UnusedArgs.push_back(Arg->getArgNo());
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}
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if (UnusedArgs.empty())
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return false;
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bool Changed = false;
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for (Function::use_iterator I = Fn.use_begin(), E = Fn.use_end();
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I != E; ++I) {
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CallSite CS(*I);
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if (!CS || !CS.isCallee(I))
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continue;
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// Now go through all unused args and replace them with "undef".
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for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
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unsigned ArgNo = UnusedArgs[I];
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Value *Arg = CS.getArgument(ArgNo);
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CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
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++NumArgumentsReplacedWithUndef;
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Changed = true;
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}
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}
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return Changed;
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}
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/// Convenience function that returns the number of return values. It returns 0
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/// for void functions and 1 for functions not returning a struct. It returns
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/// the number of struct elements for functions returning a struct.
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@ -939,5 +990,14 @@ bool DAE::runOnModule(Module &M) {
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Function *F = I++;
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Changed |= RemoveDeadStuffFromFunction(F);
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}
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// Finally, look for any unused parameters in functions with non-local
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// linkage and replace the passed in parameters with undef.
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for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
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Function& F = *I;
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Changed |= RemoveDeadArgumentsFromCallers(F);
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}
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return Changed;
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}
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@ -1,5 +1,4 @@
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; RUN: opt -deadargelim -S %s | FileCheck %s
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; XFAIL: *
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define void @test(i32) {
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ret void
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@ -11,3 +10,30 @@ define void @foo() {
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; CHECK: @foo
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; CHECK: i32 undef
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}
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define void @f(i32 %X) {
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entry:
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tail call void @sideeffect() nounwind
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ret void
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}
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declare void @sideeffect()
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define void @g(i32 %n) {
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entry:
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%add = add nsw i32 %n, 1
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; CHECK: tail call void @f(i32 undef)
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tail call void @f(i32 %add)
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ret void
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}
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define void @h() {
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entry:
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%i = alloca i32, align 4
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volatile store i32 10, i32* %i, align 4
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; CHECK: %tmp = volatile load i32* %i, align 4
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; CHECK-next: call void @f(i32 undef)
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%tmp = volatile load i32* %i, align 4
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call void @f(i32 %tmp)
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ret void
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}
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