[llvm] r211251 - Make instsimplify's analysis of icmp eq/ne use computeKnownBits to determine whether the icmp is always true or false. Patch by Suyog Sarda!

[Nick Lewycky]

Author: nicholas
Date: Wed Jun 18 22:35:49 2014
New Revision: 211251

URL: http://llvm.org/viewvc/llvm-project?rev=211251&view=rev
Log:
Make instsimplify's analysis of icmp eq/ne use computeKnownBits to determine whether the icmp is always true or false. Patch by Suyog Sarda!

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstCombine/align-2d-gep.ll
    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=211251&r1=211250&r2=211251&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Wed Jun 18 22:35:49 2014
@@ -2241,6 +2241,25 @@ static Value *SimplifyICmpInst(unsigned
     }
   }
 
+  // If a bit is known to be zero for A and known to be one for B,
+  // then A and B cannot be equal.
+  if (ICmpInst::isEquality(Pred)) {
+    if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
+      uint32_t BitWidth = CI->getBitWidth();
+      APInt LHSKnownZero(BitWidth, 0);
+      APInt LHSKnownOne(BitWidth, 0);
+      computeKnownBits(LHS, LHSKnownZero, LHSKnownOne);
+      APInt RHSKnownZero(BitWidth, 0);
+      APInt RHSKnownOne(BitWidth, 0);
+      computeKnownBits(RHS, RHSKnownZero, RHSKnownOne);
+      if (((LHSKnownOne & RHSKnownZero) != 0) ||
+          ((LHSKnownZero & RHSKnownOne) != 0))
+        return (Pred == ICmpInst::ICMP_EQ)
+                   ? ConstantInt::getFalse(CI->getContext())
+                   : ConstantInt::getTrue(CI->getContext());
+    }
+  }
+
   // Special logic for binary operators.
   BinaryOperator *LBO = dyn_cast<BinaryOperator>(LHS);
   BinaryOperator *RBO = dyn_cast<BinaryOperator>(RHS);

Modified: llvm/trunk/test/Transforms/InstCombine/align-2d-gep.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/align-2d-gep.ll?rev=211251&r1=211250&r2=211251&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/align-2d-gep.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/align-2d-gep.ll Wed Jun 18 22:35:49 2014
@@ -31,7 +31,7 @@ bb1:
   store <2 x double><double 0.0, double 0.0>, <2 x double>* %r, align 8
 
   %indvar.next = add i64 %j, 2
-  %exitcond = icmp eq i64 %indvar.next, 557
+  %exitcond = icmp eq i64 %indvar.next, 556
   br i1 %exitcond, label %bb11, label %bb1
 
 bb11:

Modified: llvm/trunk/test/Transforms/InstSimplify/compare.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/compare.ll?rev=211251&r1=211250&r2=211251&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/compare.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/compare.ll Wed Jun 18 22:35:49 2014
@@ -883,3 +883,22 @@ define i1 @returns_nonnull() {
 ; CHECK: ret i1 false
 }
 
+; If a bit is known to be zero for A and known to be one for B,
+; then A and B cannot be equal.
+define i1 @icmp_eq_const(i32 %a) nounwind {
+  %b = mul nsw i32 %a, -2
+  %c = icmp eq i32 %b, 1
+  ret i1 %c
+
+; CHECK-LABEL: @icmp_eq_const
+; CHECK-NEXT: ret i1 false 
+}
+
+define i1 @icmp_ne_const(i32 %a) nounwind {
+  %b = mul nsw i32 %a, -2
+  %c = icmp ne i32 %b, 1
+  ret i1 %c
+
+; CHECK-LABEL: @icmp_ne_const
+; CHECK-NEXT: ret i1 true
+}