[llvm] r185677 - InstCombine: (icmp eq B, 0) | (icmp ult A, B) -> (icmp ule A, B-1)

[David Majnemer]

Author: majnemer
Date: Thu Jul  4 19:31:17 2013
New Revision: 185677

URL: http://llvm.org/viewvc/llvm-project?rev=185677&view=rev
Log:
InstCombine: (icmp eq B, 0) | (icmp ult A, B) -> (icmp ule A, B-1)

This transform allows us to turn IR that looks like:
  %1 = icmp eq i64 %b, 0
  %2 = icmp ult i64 %a, %b
  %3 = or i1 %1, %2
  ret i1 %3

into:
  %0 = add i64 %b, -1
  %1 = icmp uge i64 %0, %a
  ret i1 %1

which means we go from lowering:
        cmpq    %rsi, %rdi
        setb    %cl
        testq   %rsi, %rsi
        sete    %al
        orb     %cl, %al
        ret

to lowering:
        decq    %rsi
        cmpq    %rdi, %rsi
        setae   %al
        ret

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=185677&r1=185676&r2=185677&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Thu Jul  4 19:31:17 2013
@@ -1477,10 +1477,37 @@ Value *InstCombiner::FoldOrOfICmps(ICmpI
   if (Value *V = foldLogOpOfMaskedICmps(LHS, RHS, ICmpInst::ICMP_NE, Builder))
     return V;
 
-  // This only handles icmp of constants: (icmp1 A, C1) | (icmp2 B, C2).
   Value *Val = LHS->getOperand(0), *Val2 = RHS->getOperand(0);
   ConstantInt *LHSCst = dyn_cast<ConstantInt>(LHS->getOperand(1));
   ConstantInt *RHSCst = dyn_cast<ConstantInt>(RHS->getOperand(1));
+
+  if (LHS->hasOneUse() || RHS->hasOneUse()) {
+    // (icmp eq B, 0) | (icmp ult A, B) -> (icmp ule A, B-1)
+    // (icmp eq B, 0) | (icmp ugt B, A) -> (icmp ule A, B-1)
+    Value *A = 0, *B = 0;
+    if (LHSCC == ICmpInst::ICMP_EQ && LHSCst && LHSCst->isZero()) {
+      B = Val;
+      if (RHSCC == ICmpInst::ICMP_ULT && Val == RHS->getOperand(1))
+        A = Val2;
+      else if (RHSCC == ICmpInst::ICMP_UGT && Val == Val2)
+        A = RHS->getOperand(1);
+    }
+    // (icmp ult A, B) | (icmp eq B, 0) -> (icmp ule A, B-1)
+    // (icmp ugt B, A) | (icmp eq B, 0) -> (icmp ule A, B-1)
+    else if (RHSCC == ICmpInst::ICMP_EQ && RHSCst && RHSCst->isZero()) {
+      B = Val2;
+      if (LHSCC == ICmpInst::ICMP_ULT && Val2 == LHS->getOperand(1))
+        A = Val;
+      else if (LHSCC == ICmpInst::ICMP_UGT && Val2 == Val)
+        A = LHS->getOperand(1);
+    }
+    if (A && B)
+      return Builder->CreateICmp(
+          ICmpInst::ICMP_UGE,
+          Builder->CreateAdd(B, ConstantInt::getSigned(B->getType(), -1)), A);
+  }
+
+  // This only handles icmp of constants: (icmp1 A, C1) | (icmp2 B, C2).
   if (LHSCst == 0 || RHSCst == 0) return 0;
 
   if (LHSCst == RHSCst && LHSCC == RHSCC) {

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=185677&r1=185676&r2=185677&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Thu Jul  4 19:31:17 2013
@@ -1102,3 +1102,14 @@ define i1 @icmp_shl_1_V_ult_2147483648(i
   %cmp = icmp ult i32 %shl, 2147483648
   ret i1 %cmp
 }
+
+; CEHCK: @or_icmp_eq_B_0_icmp_ult_A_B
+; CHECK: [[SUB:%[a-z0-9]+]] = add i64 %b, -1
+; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp uge i64 [[SUB]], %a
+; CHECK-NEXT: ret i1 [[CMP]]
+define i1 @or_icmp_eq_B_0_icmp_ult_A_B(i64 %a, i64 %b) {
+  %1 = icmp eq i64 %b, 0
+  %2 = icmp ult i64 %a, %b
+  %3 = or i1 %1, %2
+  ret i1 %3
+}