[ARM] Fix perf regression in compare optimization.

Fix a performance regression caused by r322737.

While trying to make it easier to replace compares with existing adds and
subtracts, I accidentally stopped it from doing so in some cases.  This should
fix that.  I'm also fixing another potential bug in that commit.

Differential Revision: https://reviews.llvm.org/D42263

llvm-svn: 322972

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 9981b0586d6..45724df9619 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -2736,7 +2736,7 @@ bool ARMBaseInstrInfo::optimizeCompareInstr(
     }
     I = CmpInstr;
     E = MI;
-  } else {
+  } else if (E != B) {
     // Allow the loop below to search E (which was initially MI).  Since MI and
     // SubAdd have different tests, even if that instruction could not be MI, it
     // could still potentially be SubAdd.
@@ -2763,8 +2763,7 @@ bool ARMBaseInstrInfo::optimizeCompareInstr(
       return false;
 
     if (I == B)
-      // The 'and' is below the comparison instruction.
-      return false;
+      break;
   }
 
   // Return false if no candidates exist.