Teach InstCombine to merge (icmp ult (X + CA), C1) | (icmp eq X, C2) into (icmp ult (X + CA), C1 + 1) if C2 + CA == C1.

InstCombine creates these so now we compile x == 23 || x == 24 || x == 25 to
  %x.off = add i32 %x, -23
  %1 = icmp ult i32 %x.off, 3
instead of
  %x.off = add i32 %x, -23
  %1 = icmp ult i32 %x.off, 2
  %cmp3 = icmp eq i32 %x, 25
  %ret2 = or i1 %1, %cmp3

llvm-svn: 122248

2 files changed, 24 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 41734f6ac9d..57fe870158b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1450,7 +1450,16 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
       return Builder->CreateICmp(LHSCC, NewOr, LHSCst);
     }
   }
-  
+
+  // (icmp ult (X + CA), C1) | (icmp eq X, C2) -> (icmp ult (X + CA), C1 + 1)
+  //   iff C2 + CA == C1.
+  if (LHSCC == ICmpInst::ICMP_ULT) {
+    ConstantInt *AddCst;
+    if (match(Val, m_Add(m_Specific(Val2), m_ConstantInt(AddCst))))
+      if (RHSCst->getValue() + AddCst->getValue() == LHSCst->getValue())
+        return Builder->CreateICmp(LHSCC, Val, AddOne(LHSCst));
+  }
+
   // From here on, we only handle:
   //    (icmp1 A, C1) | (icmp2 A, C2) --> something simpler.
   if (Val != Val2) return 0;
diff --git a/llvm/test/Transforms/InstCombine/or.ll b/llvm/test/Transforms/InstCombine/or.ll
index 500cad2ad64..f82f9faab2d 100644
--- a/llvm/test/Transforms/InstCombine/or.ll
+++ b/llvm/test/Transforms/InstCombine/or.ll
@@ -376,3 +376,17 @@ define i32 @test35(i32 %a, i32 %b) {
   ; CHECK-NEXT: or i32 %a, %b
   ; CHECK-NEXT: or i32 %1, 1135
 }
+
+define i1 @test36(i32 %x) {
+  %cmp1 = icmp eq i32 %x, 23
+  %cmp2 = icmp eq i32 %x, 24
+  %ret1 = or i1 %cmp1, %cmp2
+  %cmp3 = icmp eq i32 %x, 25
+  %ret2 = or i1 %ret1, %cmp3
+  ret i1 %ret2
+; CHECK: @test36
+; CHECK-NEXT: %x.off = add i32 %x, -23
+; CHECK-NEXT: icmp ult i32 %x.off, 3
+; CHECK-NEXT: ret i1
+}
+