[llvm-commits] [llvm] r126741 - in /llvm/trunk: lib/Analysis/InstructionSimplify.cpp test/Transforms/InstSimplify/compare.ll

[Nick Lewycky]

Author: nicholas
Date: Tue Mar  1 02:15:50 2011
New Revision: 126741

URL: http://llvm.org/viewvc/llvm-project?rev=126741&view=rev
Log:
Optimize "icmp pred (urem X, Y), Y" --> true/false depending on pred. There's
more work to do here, "icmp ult (urem X, 10), 11" doesn't optimize away yet.
Fixes example 3 from PR9343!

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/compare.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=126741&r1=126740&r2=126741&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Tue Mar  1 02:15:50 2011
@@ -1434,6 +1434,9 @@
         return ConstantInt::getTrue(CI->getContext());
       break;
     }
+
+    // TODO: integer div and rem with constant RHS all produce values in a
+    // constant range. We should check whether the comparison is a tautology.
   }
 
   // Compare of cast, for example (zext X) != 0 -> X != 0
@@ -1644,6 +1647,21 @@
     }
   }
 
+  if (LBO && match(LBO, m_URem(m_Value(), m_Specific(RHS)))) {
+    switch (Pred) {
+    default:
+      break;
+    case ICmpInst::ICMP_EQ:
+    case ICmpInst::ICMP_UGT:
+    case ICmpInst::ICMP_UGE:
+      return ConstantInt::getFalse(RHS->getContext());
+    case ICmpInst::ICMP_NE:
+    case ICmpInst::ICMP_ULT:
+    case ICmpInst::ICMP_ULE:
+      return ConstantInt::getTrue(RHS->getContext());
+    }
+  }
+
   // If the comparison is with the result of a select instruction, check whether
   // comparing with either branch of the select always yields the same value.
   if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))

Modified: llvm/trunk/test/Transforms/InstSimplify/compare.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/compare.ll?rev=126741&r1=126740&r2=126741&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/compare.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/compare.ll Tue Mar  1 02:15:50 2011
@@ -187,3 +187,19 @@
   ret i1 %c
 ; CHECK: ret i1 %cond
 }
+
+define i1 @urem1(i32 %X, i32 %Y) {
+; CHECK: @urem1
+  %A = urem i32 %X, %Y
+  %B = icmp ult i32 %A, %Y
+  ret i1 %B
+; CHECK: ret i1 true
+}
+
+define i1 @urem2(i32 %X, i32 %Y) {
+; CHECK: @urem2
+  %A = urem i32 %X, %Y
+  %B = icmp eq i32 %A, %Y
+  ret i1 %B
+; CHECK ret i1 false
+}