[SystemZ] Use BRCT and BRCTG to eliminate add-&-compare sequences
This patch just uses a peephole test for "add; compare; branch" sequences
within a single block. The IR optimizers already convert loops to
decrement-and-branch-on-nonzero form in some cases, so even this
simplistic test triggers many times during a clang bootstrap and
projects/test-suite run. It looks like there are still cases where we
need to more strongly prefer branches on nonzero though. E.g. I saw a
case where a loop that started out with a check for 0 ended up with a
check for -1. I'll try to look at that sometime.
I ended up adding the Reference class because MachineInstr::readsRegister()
doesn't check for subregisters (by design, as far as I could tell).
llvm-svn: 187723
diff --git a/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp b/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
index 5dd8d98..c2a6a7f 100644
--- a/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp
@@ -684,6 +684,14 @@
MI->getOperand(0).getImm(),
MI->getOperand(1).getImm(), &MI->getOperand(2));
+ case SystemZ::BRCT:
+ return SystemZII::Branch(SystemZII::BranchCT, SystemZ::CCMASK_ICMP,
+ SystemZ::CCMASK_CMP_NE, &MI->getOperand(2));
+
+ case SystemZ::BRCTG:
+ return SystemZII::Branch(SystemZII::BranchCTG, SystemZ::CCMASK_ICMP,
+ SystemZ::CCMASK_CMP_NE, &MI->getOperand(2));
+
case SystemZ::CIJ:
case SystemZ::CRJ:
return SystemZII::Branch(SystemZII::BranchC, SystemZ::CCMASK_ICMP,