diff --git a/lib/CodeGen/EarlyIfConversion.cpp b/lib/CodeGen/EarlyIfConversion.cpp index d3687b98b34..fbc4d97c498 100644 --- a/lib/CodeGen/EarlyIfConversion.cpp +++ b/lib/CodeGen/EarlyIfConversion.cpp @@ -479,11 +479,20 @@ void SSAIfConv::rewritePHIOperands() { // Convert all PHIs to select instructions inserted before FirstTerm. for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { PHIInfo &PI = PHIs[i]; + unsigned DstReg = 0; + DEBUG(dbgs() << "If-converting " << *PI.PHI); - unsigned PHIDst = PI.PHI->getOperand(0).getReg(); - unsigned DstReg = MRI->createVirtualRegister(MRI->getRegClass(PHIDst)); - TII->insertSelect(*Head, FirstTerm, HeadDL, DstReg, Cond, PI.TReg, PI.FReg); - DEBUG(dbgs() << " --> " << *std::prev(FirstTerm)); + if (PI.TReg == PI.FReg) { + // We do not need the select instruction if both incoming values are + // equal. + DstReg = PI.TReg; + } else { + unsigned PHIDst = PI.PHI->getOperand(0).getReg(); + DstReg = MRI->createVirtualRegister(MRI->getRegClass(PHIDst)); + TII->insertSelect(*Head, FirstTerm, HeadDL, + DstReg, Cond, PI.TReg, PI.FReg); + DEBUG(dbgs() << " --> " << *std::prev(FirstTerm)); + } // Rewrite PHI operands TPred -> (DstReg, Head), remove FPred. for (unsigned i = PI.PHI->getNumOperands(); i != 1; i -= 2) { diff --git a/test/CodeGen/AArch64/ifcvt-select.ll b/test/CodeGen/AArch64/ifcvt-select.ll new file mode 100644 index 00000000000..4e024d963f2 --- /dev/null +++ b/test/CodeGen/AArch64/ifcvt-select.ll @@ -0,0 +1,41 @@ +; RUN: llc -mtriple=arm64-apple-ios -mcpu=cyclone < %s | FileCheck %s +; Do not generate redundant select in early if-converstion pass. + +define i32 @foo(i32 %a, i32 %b) { +entry: +;CHECK-LABEL: foo: +;CHECK: csinc +;CHECK-NOT: csel + %sub = sub nsw i32 %b, %a + %cmp10 = icmp sgt i32 %a, 0 + br i1 %cmp10, label %while.body.lr.ph, label %while.end + +while.body.lr.ph: + br label %while.body + +while.body: + %j.012 = phi i32 [ %sub, %while.body.lr.ph ], [ %inc, %if.then ], [ %inc, %if.else ] + %i.011 = phi i32 [ %a, %while.body.lr.ph ], [ %inc2, %if.then ], [ %dec, %if.else ] + %cmp1 = icmp slt i32 %i.011, %j.012 + br i1 %cmp1, label %while.end, label %while.cond + +while.cond: + %inc = add nsw i32 %j.012, 5 + %cmp2 = icmp slt i32 %inc, %b + br i1 %cmp2, label %if.then, label %if.else + +if.then: + %inc2 = add nsw i32 %i.011, 1 + br label %while.body + +if.else: + %dec = add nsw i32 %i.011, -1 + br label %while.body + +while.end: + %j.0.lcssa = phi i32 [ %j.012, %while.body ], [ %sub, %entry ] + %i.0.lcssa = phi i32 [ %i.011, %while.body ], [ %a, %entry ] + %add = add nsw i32 %j.0.lcssa, %i.0.lcssa + ret i32 %add +} +