From b0765d6ac0140718cd8d5b896504fd89ce0594d2 Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Sun, 12 Jun 2011 22:48:00 +0000
Subject: [PATCH] InstCombine: Shrink ((zext X) & C1) == C2 to fold away the
 cast if the "zext" and the "and" have one use.

llvm-svn: 132897
---
 .../InstCombine/InstCombineCompares.cpp        | 18 +++++++++++++++++-
 test/Transforms/InstCombine/icmp.ll            | 10 ++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 92cbc1b7f18..5ddf23ba8e1 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1097,7 +1097,23 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
                               ConstantExpr::getZExt(RHS, Cast->getSrcTy()));
         }
       }
-      
+
+      // If the LHS is an AND of a zext, and we have an equality compare, we can
+      // shrink the and/compare to the smaller type, eliminating the cast.
+      if (ZExtInst *Cast = dyn_cast<ZExtInst>(LHSI->getOperand(0))) {
+        const IntegerType *Ty = cast<IntegerType>(Cast->getSrcTy());
+        // Make sure we don't compare the upper bits, SimplifyDemandedBits
+        // should fold the icmp to true/false in that case.
+        if (ICI.isEquality() && RHSV.getActiveBits() <= Ty->getBitWidth()) {
+          Value *NewAnd =
+            Builder->CreateAnd(Cast->getOperand(0),
+                               ConstantExpr::getTrunc(AndCST, Ty));
+          NewAnd->takeName(LHSI);
+          return new ICmpInst(ICI.getPredicate(), NewAnd,
+                              ConstantExpr::getTrunc(RHS, Ty));
+        }
+      }
+
       // If this is: (X >> C1) & C2 != C3 (where any shift and any compare
       // could exist), turn it into (X & (C2 << C1)) != (C3 << C1).  This
       // happens a LOT in code produced by the C front-end, for bitfield
diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index 1237adee74d..ecbba23091c 100644
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/test/Transforms/InstCombine/icmp.ll
@@ -521,3 +521,13 @@ define i1 @test53(i32 %a, i32 %b) nounwind {
  %z = icmp eq i32 %x, %y
  ret i1 %z
 }
+
+; CHECK: @test54
+; CHECK-NEXT: %and = and i8 %a, -64
+; CHECK-NEXT icmp eq i8 %and, -128
+define i1 @test54(i8 %a) nounwind {
+  %ext = zext i8 %a to i32
+  %and = and i32 %ext, 192
+  %ret = icmp eq i32 %and, 128
+  ret i1 %ret
+}