From 56bd02c55c7e512e140003015ab201441ef9eeac Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 18 Jun 2009 16:30:21 +0000
Subject: [PATCH] Generalize the zext(trunc(t) & C) instcombine to work even
 with C is not a low-bits mask, and add a similar instcombine for
 zext((trunc(t) & C) ^ C).

llvm-svn: 73705
---
 .../Scalar/InstructionCombining.cpp           | 29 ++++++++++++++-----
 .../Transforms/InstCombine/trunc-mask-ext.ll  | 17 ++++++++++-
 2 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index bf287f2c6808..5bd17e0737b2 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -8564,20 +8564,33 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
     }
   }
 
-  // zext(trunc(t) & C) -> (t & C)  if C is a mask.
+  // zext(trunc(t) & C) -> (t & zext(C)).
   if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse())
     if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
       if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) {
         Value *TI0 = TI->getOperand(0);
-        if (TI0->getType() == CI.getType()) {
-          unsigned TO = C->getValue().countTrailingOnes();
-          if (APIntOps::isMask(TO, C->getValue()))
-            return
-              BinaryOperator::Create(Instruction::And, TI0,
-                                     ConstantExpr::getZExt(C, CI.getType()));
-        }
+        if (TI0->getType() == CI.getType())
+          return
+            BinaryOperator::CreateAnd(TI0,
+                                      ConstantExpr::getZExt(C, CI.getType()));
       }
 
+  // zext((trunc(t) & C) ^ C) -> ((t & zext(C)) ^ zext(C)).
+  if (SrcI && SrcI->getOpcode() == Instruction::Xor && SrcI->hasOneUse())
+    if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
+      if (BinaryOperator *And = dyn_cast<BinaryOperator>(SrcI->getOperand(0)))
+        if (And->getOpcode() == Instruction::And && And->hasOneUse() &&
+            And->getOperand(1) == C)
+          if (TruncInst *TI = dyn_cast<TruncInst>(And->getOperand(0))) {
+            Value *TI0 = TI->getOperand(0);
+            if (TI0->getType() == CI.getType()) {
+              Constant *ZC = ConstantExpr::getZExt(C, CI.getType());
+              Instruction *NewAnd = BinaryOperator::CreateAnd(TI0, ZC, "tmp");
+              InsertNewInstBefore(NewAnd, *And);
+              return BinaryOperator::CreateXor(NewAnd, ZC);
+            }
+          }
+
   return 0;
 }
 
diff --git a/llvm/test/Transforms/InstCombine/trunc-mask-ext.ll b/llvm/test/Transforms/InstCombine/trunc-mask-ext.ll
index 1499947cc072..7e3d8446acff 100644
--- a/llvm/test/Transforms/InstCombine/trunc-mask-ext.ll
+++ b/llvm/test/Transforms/InstCombine/trunc-mask-ext.ll
@@ -2,7 +2,7 @@
 ; RUN: not grep zext %t
 ; RUN: not grep sext %t
 
-; Instcombine should be able to eliminate both ext casts.
+; Instcombine should be able to eliminate all of these ext casts.
 
 declare void @use(i32)
 
@@ -21,3 +21,18 @@ define i64 @bar(i64 %a) {
   call void @use(i32 %b)
   ret i64 %d
 }
+define i64 @goo(i64 %a) {
+  %b = trunc i64 %a to i32
+  %c = and i32 %b, 8
+  %d = zext i32 %c to i64
+  call void @use(i32 %b)
+  ret i64 %d
+}
+define i64 @hoo(i64 %a) {
+  %b = trunc i64 %a to i32
+  %c = and i32 %b, 8
+  %x = xor i32 %c, 8
+  %d = zext i32 %x to i64
+  call void @use(i32 %b)
+  ret i64 %d
+}