From: Chris Lattner <sabre@nondot.org>
Date: Sun, 10 Jan 2010 02:22:12 +0000 (+0000)
Subject: enhance CanEvaluateZExtd to handle shift left and sext, allowing
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=d26c9e183e56d09f48d7074be4cacce099338316;p=oota-llvm.git

enhance CanEvaluateZExtd to handle shift left and sext, allowing
more expressions to be promoted and casts eliminated.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93096 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index a6833b88257..3ad786b6bdd 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -643,17 +643,31 @@ static int CanEvaluateZExtd(Value *V, const Type *Ty,unsigned &NumCastsRemoved,
     if (Tmp1 == -1) return -1;
     Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
     if (Tmp2 == -1) return -1;
+    return 0; // TODO: Could be improved.
+      
+  case Instruction::Shl:
+    Tmp1 = CanEvaluateZExtd(I->getOperand(0), Ty, NumCastsRemoved, TD);
+    if (Tmp1 == -1) return -1;
+      
+    if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1)))
+      return Tmp1 - CI->getZExtValue();
+
+    // Variable shift, no known zext bits.
+    Tmp2 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
+    if (Tmp2 == -1) return -1;
     return 0;
       
-  //case Instruction::Shl:
   //case Instruction::LShr:
   case Instruction::ZExt:
     // zext(zext(x)) -> zext(x).  Since we're replacing it, it isn't eliminated.
     Tmp1 = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits();
     return GetLeadingZeros(I, TD)+Tmp1;
       
-  //case Instruction::SExt:  zext(sext(x)) -> sext(x) with no upper bits known.
-  //case Instruction::Trunc:
+  case Instruction::SExt:
+    // zext(sext(x)) -> sext(x) with no upper bits known.
+    return 0;
+  //case Instruction::Trunc: -> Could turn into AND.
+      
   case Instruction::Select:
     Tmp1 = CanEvaluateZExtd(I->getOperand(1), Ty, NumCastsRemoved, TD);
     if (Tmp1 == -1) return -1;
diff --git a/test/Transforms/InstCombine/cast.ll b/test/Transforms/InstCombine/cast.ll
index b6dc4642b8e..490df8fab6e 100644
--- a/test/Transforms/InstCombine/cast.ll
+++ b/test/Transforms/InstCombine/cast.ll
@@ -403,3 +403,31 @@ define i64 @test44(i8 %T) {
 ; CHECK-NEXT: %B = or i64 %A, 1234
 ; CHECK-NEXT: ret i64 %B
 }
+
+define i64 @test45(i8 %A, i64 %Q) {
+ %D = trunc i64 %Q to i32  ;; should be removed
+ %B = sext i8 %A to i32
+ %C = or i32 %B, %D
+ %E = zext i32 %C to i64 
+ ret i64 %E
+; CHECK: @test45
+; CHECK-NEXT: %B = sext i8 %A to i64
+; CHECK-NEXT: %C = or i64 %B, %Q
+; CHECK-NEXT: %E = and i64 %C, 4294967295
+; CHECK-NEXT: ret i64 %E
+}
+
+
+define i64 @test46(i64 %A) {
+ %B = trunc i64 %A to i32
+ %C = and i32 %B, 42
+ %D = shl i32 %C, 8
+ %E = zext i32 %D to i64 
+ ret i64 %E
+; CHECK: @test46
+; CHECK-NEXT: %C = shl i64 %A, 8
+; CHECK-NEXT: %D = and i64 %C, 10752
+; CHECK-NEXT: ret i64 %D
+}
+
+