+void SystemZPassConfig::addPreEmitPass() {
+ // We eliminate comparisons here rather than earlier because some
+ // transformations can change the set of available CC values and we
+ // generally want those transformations to have priority. This is
+ // especially true in the commonest case where the result of the comparison
+ // is used by a single in-range branch instruction, since we will then
+ // be able to fuse the compare and the branch instead.
+ //
+ // For example, two-address NILF can sometimes be converted into
+ // three-address RISBLG. NILF produces a CC value that indicates whether
+ // the low word is zero, but RISBLG does not modify CC at all. On the
+ // other hand, 64-bit ANDs like NILL can sometimes be converted to RISBG.
+ // The CC value produced by NILL isn't useful for our purposes, but the
+ // value produced by RISBG can be used for any comparison with zero
+ // (not just equality). So there are some transformations that lose
+ // CC values (while still being worthwhile) and others that happen to make
+ // the CC result more useful than it was originally.
+ //
+ // Another reason is that we only want to use BRANCH ON COUNT in cases
+ // where we know that the count register is not going to be spilled.
+ //
+ // Doing it so late makes it more likely that a register will be reused
+ // between the comparison and the branch, but it isn't clear whether
+ // preventing that would be a win or not.
+ if (getOptLevel() != CodeGenOpt::None)
+ addPass(createSystemZElimComparePass(getSystemZTargetMachine()), false);
+ if (getOptLevel() != CodeGenOpt::None)
+ addPass(createSystemZShortenInstPass(getSystemZTargetMachine()), false);
+ addPass(createSystemZLongBranchPass(getSystemZTargetMachine()));
+}
+
+TargetPassConfig *SystemZTargetMachine::createPassConfig(PassManagerBase &PM) {
+ return new SystemZPassConfig(this, PM);
+}