ARM/Thumb2: Fix a misselect in getARMCmp, when attempting to adjust a signed

comparison that would overflow.
 - The other under/overflow cases can't actually happen because the immediates
   which would trigger them are legal (so we don't enter this code), but
   adjusted the style to make it clear the transform is always valid.

llvm-svn: 112053

2 files changed, 18 insertions, 4 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 034114c680c..5a10b728d4f 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -2271,28 +2271,28 @@ ARMTargetLowering::getARMCmp(SDValue LHS, SDValue RHS, ISD::CondCode CC,
       default: break;
       case ISD::SETLT:
       case ISD::SETGE:
-        if (isLegalICmpImmediate(C-1)) {
+        if (C != 0x80000000 && isLegalICmpImmediate(C-1)) {
           CC = (CC == ISD::SETLT) ? ISD::SETLE : ISD::SETGT;
           RHS = DAG.getConstant(C-1, MVT::i32);
         }
         break;
       case ISD::SETULT:
       case ISD::SETUGE:
-        if (C > 0 && isLegalICmpImmediate(C-1)) {
+        if (C != 0 && isLegalICmpImmediate(C-1)) {
           CC = (CC == ISD::SETULT) ? ISD::SETULE : ISD::SETUGT;
           RHS = DAG.getConstant(C-1, MVT::i32);
         }
         break;
       case ISD::SETLE:
       case ISD::SETGT:
-        if (isLegalICmpImmediate(C+1)) {
+        if (C != 0x7fffffff && isLegalICmpImmediate(C+1)) {
           CC = (CC == ISD::SETLE) ? ISD::SETLT : ISD::SETGE;
           RHS = DAG.getConstant(C+1, MVT::i32);
         }
         break;
       case ISD::SETULE:
       case ISD::SETUGT:
-        if (C < 0xffffffff && isLegalICmpImmediate(C+1)) {
+        if (C != 0xffffffff && isLegalICmpImmediate(C+1)) {
           CC = (CC == ISD::SETULE) ? ISD::SETULT : ISD::SETUGE;
           RHS = DAG.getConstant(C+1, MVT::i32);
         }
diff --git a/llvm/test/CodeGen/Thumb2/thumb2-cmp.ll b/llvm/test/CodeGen/Thumb2/thumb2-cmp.ll
index d4773bb5809..63249f4cf14 100644
--- a/llvm/test/CodeGen/Thumb2/thumb2-cmp.ll
+++ b/llvm/test/CodeGen/Thumb2/thumb2-cmp.ll
@@ -39,3 +39,17 @@ define i1 @f5(i32 %a) {
     %tmp = icmp eq i32 %a, 1114112
     ret i1 %tmp
 }
+
+; Check that we don't do an invalid (a > b) --> !(a < b + 1) transform.
+;
+; CHECK: f6:
+; CHECK-NOT: cmp.w r0, #-2147483648
+; CHECK: bx lr
+define i32 @f6(i32 %a) {
+    %tmp = icmp sgt i32 %a, 2147483647
+    br i1 %tmp, label %true, label %false
+true:
+    ret i32 2
+false:
+    ret i32 0
+}